"Lots of cleanups and preparation; highlights:
- futex: Cleanup and remove runtime futex_cmpxchg detection
- rtmutex: Some fixes for the PREEMPT_RT locking infrastructure
- kcsan: Share owner_on_cpu() between mutex,rtmutex and rwsem and
annotate the racy owner->on_cpu access *once*.
- atomic64: Dead-Code-Elemination"
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Merge tag 'locking_core_for_v5.17_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Borislav Petkov:
"Lots of cleanups and preparation. Highlights:
- futex: Cleanup and remove runtime futex_cmpxchg detection
- rtmutex: Some fixes for the PREEMPT_RT locking infrastructure
- kcsan: Share owner_on_cpu() between mutex,rtmutex and rwsem and
annotate the racy owner->on_cpu access *once*.
- atomic64: Dead-Code-Elemination"
[ Description above by Peter Zijlstra ]
* tag 'locking_core_for_v5.17_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
locking/atomic: atomic64: Remove unusable atomic ops
futex: Fix additional regressions
locking: Allow to include asm/spinlock_types.h from linux/spinlock_types_raw.h
x86/mm: Include spinlock_t definition in pgtable.
locking: Mark racy reads of owner->on_cpu
locking: Make owner_on_cpu() into <linux/sched.h>
lockdep/selftests: Adapt ww-tests for PREEMPT_RT
lockdep/selftests: Skip the softirq related tests on PREEMPT_RT
lockdep/selftests: Unbalanced migrate_disable() & rcu_read_lock().
lockdep/selftests: Avoid using local_lock_{acquire|release}().
lockdep: Remove softirq accounting on PREEMPT_RT.
locking/rtmutex: Add rt_mutex_lock_nest_lock() and rt_mutex_lock_killable().
locking/rtmutex: Squash self-deadlock check for ww_rt_mutex.
locking: Remove rt_rwlock_is_contended().
sched: Trigger warning if ->migration_disabled counter underflows.
futex: Fix sparc32/m68k/nds32 build regression
futex: Remove futex_cmpxchg detection
futex: Ensure futex_atomic_cmpxchg_inatomic() is present
kernel/locking: Use a pointer in ww_mutex_trylock().
This pull request contains the following branches:
doc.2021.11.30c: Documentation updates, perhaps most notably Neil Brown's
writeup of the reference-counting analogy to RCU.
exp.2021.12.07a: Expedited grace-period cleanups.
fastnohz.2021.11.30c: Remove CONFIG_RCU_FAST_NO_HZ due to lack of valid
users. I have asked around, posted a blog entry, and sent this
series to LKML without result.
fixes.2021.11.30c: Miscellaneous fixes.
nocb.2021.12.09a: RCU callback offloading updates, perhaps most notably
Frederic Weisbecker's updates allowing CPUs booted in the
de-offloaded state to be offloaded at runtime.
nolibc.2021.11.30c: nolibc fixes from Willy Tarreau and Anmar Faizi, but
also including Mark Brown's addition of gettid().
tasks.2021.12.09a: RCU Tasks Trace fixes, including changes that increase
the scalability of call_rcu_tasks_trace() for the BPF folks
(Martin Lau and KP Singh).
torture.2021.12.07a: Various fixes including those from Wander Lairson
Costa and Li Zhijian.
torturescript.2021.11.30c: Fixes plus addition of tests for the increased
call_rcu_tasks_trace() scalability.
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Merge tag 'rcu.2022.01.09a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu
Pull RCU updates from Paul McKenney:
- Documentation updates, perhaps most notably Neil Brown's writeup of
the reference-counting analogy to RCU.
- Expedited grace-period cleanups.
- Remove CONFIG_RCU_FAST_NO_HZ due to lack of valid users. I have asked
around, posted a blog entry, and sent this series to LKML without
result.
- Miscellaneous fixes.
- RCU callback offloading updates, perhaps most notably Frederic
Weisbecker's updates allowing CPUs booted in the de-offloaded state
to be offloaded at runtime.
- nolibc fixes from Willy Tarreau and Anmar Faizi, but also including
Mark Brown's addition of gettid().
- RCU Tasks Trace fixes, including changes that increase the
scalability of call_rcu_tasks_trace() for the BPF folks (Martin Lau
and KP Singh).
- Various fixes including those from Wander Lairson Costa and Li
Zhijian.
- Fixes plus addition of tests for the increased call_rcu_tasks_trace()
scalability.
* tag 'rcu.2022.01.09a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (87 commits)
rcu/nocb: Merge rcu_spawn_cpu_nocb_kthread() and rcu_spawn_one_nocb_kthread()
rcu/nocb: Allow empty "rcu_nocbs" kernel parameter
rcu/nocb: Create kthreads on all CPUs if "rcu_nocbs=" or "nohz_full=" are passed
rcu/nocb: Optimize kthreads and rdp initialization
rcu/nocb: Prepare nocb_cb_wait() to start with a non-offloaded rdp
rcu/nocb: Remove rcu_node structure from nocb list when de-offloaded
rcu-tasks: Use fewer callbacks queues if callback flood ends
rcu-tasks: Use separate ->percpu_dequeue_lim for callback dequeueing
rcu-tasks: Use more callback queues if contention encountered
rcu-tasks: Avoid raw-spinlocked wakeups from call_rcu_tasks_generic()
rcu-tasks: Count trylocks to estimate call_rcu_tasks() contention
rcu-tasks: Add rcupdate.rcu_task_enqueue_lim to set initial queueing
rcu-tasks: Make rcu_barrier_tasks*() handle multiple callback queues
rcu-tasks: Use workqueues for multiple rcu_tasks_invoke_cbs() invocations
rcu-tasks: Abstract invocations of callbacks
rcu-tasks: Abstract checking of callback lists
rcu-tasks: Add a ->percpu_enqueue_lim to the rcu_tasks structure
rcu-tasks: Inspect stalled task's trc state in locked state
rcu-tasks: Use spin_lock_rcu_node() and friends
rcutorture: Combine n_max_cbs from all kthreads in a callback flood
...
Optimistic spinning needs to be terminated when the spinning waiter is not
longer the top waiter on the lock, but the condition is negated. It
terminates if the waiter is the top waiter, which is defeating the whole
purpose.
Fixes: c3123c4314 ("locking/rtmutex: Dont dereference waiter lockless")
Signed-off-by: Zqiang <qiang1.zhang@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20211217074207.77425-1-qiang1.zhang@intel.com
Unconditionally log messages corresponding to errors.
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Li Zhijian <zhijianx.li@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Move the owner_on_cpu() from kernel/locking/rwsem.c into
include/linux/sched.h with under CONFIG_SMP, then use it
in the mutex/rwsem/rtmutex to simplify the code.
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20211203075935.136808-2-wangkefeng.wang@huawei.com
There is not really a softirq context on PREEMPT_RT. Softirqs on
PREEMPT_RT are always invoked within the context of a threaded
interrupt handler or within ksoftirqd. The "in-softirq" context is
preemptible and is protected by a per-CPU lock to ensure mutual
exclusion.
There is no difference on PREEMPT_RT between spin_lock_irq() and
spin_lock() because the former does not disable interrupts. Therefore
if a lock is used in_softirq() and locked once with spin_lock_irq()
then lockdep will report this with "inconsistent {SOFTIRQ-ON-W} ->
{IN-SOFTIRQ-W} usage".
Teach lockdep that we don't really do softirqs on -RT.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20211129174654.668506-6-bigeasy@linutronix.de
The locking selftest for ww-mutex expects to operate directly on the
base-mutex which becomes a rtmutex on PREEMPT_RT.
Add a rtmutex based implementation of mutex_lock_nest_lock() and
mutex_lock_killable() named rt_mutex_lock_nest_lock() abd
rt_mutex_lock_killable().
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20211129174654.668506-5-bigeasy@linutronix.de
Similar to the issues in commits:
6467822b8c ("locking/rtmutex: Prevent spurious EDEADLK return caused by ww_mutexes")
a055fcc132 ("locking/rtmutex: Return success on deadlock for ww_mutex waiters")
ww_rt_mutex_lock() should not return EDEADLK without first going through
the __ww_mutex logic to set the required state. In fact, the chain-walk
can deal with the spurious cycles (per the above commits) this check
warns about and is trying to avoid.
Therefore ignore this test for ww_rt_mutex and simply let things fall
in place.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20211129174654.668506-4-bigeasy@linutronix.de
rt_rwlock_is_contended() has no users. It makes no sense to use it as
rwlock_is_contended() because it is a sleeping lock on RT and
preemption is possible. It reports always != 0 if used by a writer and
even if there is a waiter then the lock might not be handed over if
the current owner has the highest priority.
Remove rt_rwlock_is_contended().
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20211129174654.668506-3-bigeasy@linutronix.de
We found that a process with 10 thousnads threads has been encountered
a regression problem from Linux-v4.14 to Linux-v5.4. It is a kind of
workload which will concurrently allocate lots of memory in different
threads sometimes. In this case, we will see the down_read_trylock()
with a high hotspot. Therefore, we suppose that rwsem has a regression
at least since Linux-v5.4. In order to easily debug this problem, we
write a simply benchmark to create the similar situation lile the
following.
```c++
#include <sys/mman.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sched.h>
#include <cstdio>
#include <cassert>
#include <thread>
#include <vector>
#include <chrono>
volatile int mutex;
void trigger(int cpu, char* ptr, std::size_t sz)
{
cpu_set_t set;
CPU_ZERO(&set);
CPU_SET(cpu, &set);
assert(pthread_setaffinity_np(pthread_self(), sizeof(set), &set) == 0);
while (mutex);
for (std::size_t i = 0; i < sz; i += 4096) {
*ptr = '\0';
ptr += 4096;
}
}
int main(int argc, char* argv[])
{
std::size_t sz = 100;
if (argc > 1)
sz = atoi(argv[1]);
auto nproc = std:🧵:hardware_concurrency();
std::vector<std::thread> thr;
sz <<= 30;
auto* ptr = mmap(nullptr, sz, PROT_READ | PROT_WRITE, MAP_ANON |
MAP_PRIVATE, -1, 0);
assert(ptr != MAP_FAILED);
char* cptr = static_cast<char*>(ptr);
auto run = sz / nproc;
run = (run >> 12) << 12;
mutex = 1;
for (auto i = 0U; i < nproc; ++i) {
thr.emplace_back(std::thread([i, cptr, run]() { trigger(i, cptr, run); }));
cptr += run;
}
rusage usage_start;
getrusage(RUSAGE_SELF, &usage_start);
auto start = std::chrono::system_clock::now();
mutex = 0;
for (auto& t : thr)
t.join();
rusage usage_end;
getrusage(RUSAGE_SELF, &usage_end);
auto end = std::chrono::system_clock::now();
timeval utime;
timeval stime;
timersub(&usage_end.ru_utime, &usage_start.ru_utime, &utime);
timersub(&usage_end.ru_stime, &usage_start.ru_stime, &stime);
printf("usr: %ld.%06ld\n", utime.tv_sec, utime.tv_usec);
printf("sys: %ld.%06ld\n", stime.tv_sec, stime.tv_usec);
printf("real: %lu\n",
std::chrono::duration_cast<std::chrono::milliseconds>(end -
start).count());
return 0;
}
```
The functionality of above program is simply which creates `nproc`
threads and each of them are trying to touch memory (trigger page
fault) on different CPU. Then we will see the similar profile by
`perf top`.
25.55% [kernel] [k] down_read_trylock
14.78% [kernel] [k] handle_mm_fault
13.45% [kernel] [k] up_read
8.61% [kernel] [k] clear_page_erms
3.89% [kernel] [k] __do_page_fault
The highest hot instruction, which accounts for about 92%, in
down_read_trylock() is cmpxchg like the following.
91.89 │ lock cmpxchg %rdx,(%rdi)
Sice the problem is found by migrating from Linux-v4.14 to Linux-v5.4,
so we easily found that the commit ddb20d1d3a ("locking/rwsem: Optimize
down_read_trylock()") caused the regression. The reason is that the
commit assumes the rwsem is not contended at all. But it is not always
true for mmap lock which could be contended with thousands threads.
So most threads almost need to run at least 2 times of "cmpxchg" to
acquire the lock. The overhead of atomic operation is higher than
non-atomic instructions, which caused the regression.
By using the above benchmark, the real executing time on a x86-64 system
before and after the patch were:
Before Patch After Patch
# of Threads real real reduced by
------------ ------ ------ ----------
1 65,373 65,206 ~0.0%
4 15,467 15,378 ~0.5%
40 6,214 5,528 ~11.0%
For the uncontended case, the new down_read_trylock() is the same as
before. For the contended cases, the new down_read_trylock() is faster
than before. The more contended, the more fast.
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20211118094455.9068-1-songmuchun@bytedance.com
There are some inconsistency in the way that the handoff bit is being
handled in readers and writers that lead to a race condition.
Firstly, when a queue head writer set the handoff bit, it will clear
it when the writer is being killed or interrupted on its way out
without acquiring the lock. That is not the case for a queue head
reader. The handoff bit will simply be inherited by the next waiter.
Secondly, in the out_nolock path of rwsem_down_read_slowpath(), both
the waiter and handoff bits are cleared if the wait queue becomes
empty. For rwsem_down_write_slowpath(), however, the handoff bit is
not checked and cleared if the wait queue is empty. This can
potentially make the handoff bit set with empty wait queue.
Worse, the situation in rwsem_down_write_slowpath() relies on wstate,
a variable set outside of the critical section containing the ->count
manipulation, this leads to race condition where RWSEM_FLAG_HANDOFF
can be double subtracted, corrupting ->count.
To make the handoff bit handling more consistent and robust, extract
out handoff bit clearing code into the new rwsem_del_waiter() helper
function. Also, completely eradicate wstate; always evaluate
everything inside the same critical section.
The common function will only use atomic_long_andnot() to clear bits
when the wait queue is empty to avoid possible race condition. If the
first waiter with handoff bit set is killed or interrupted to exit the
slowpath without acquiring the lock, the next waiter will inherit the
handoff bit.
While at it, simplify the trylock for loop in
rwsem_down_write_slowpath() to make it easier to read.
Fixes: 4f23dbc1e6 ("locking/rwsem: Implement lock handoff to prevent lock starvation")
Reported-by: Zhenhua Ma <mazhenhua@xiaomi.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20211116012912.723980-1-longman@redhat.com
mutex_acquire_nest() expects a pointer, pass the pointer.
Fixes: 12235da8c8 ("kernel/locking: Add context to ww_mutex_trylock()")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20211104122706.frk52zxbjorso2kv@linutronix.de
Merge more updates from Andrew Morton:
"87 patches.
Subsystems affected by this patch series: mm (pagecache and hugetlb),
procfs, misc, MAINTAINERS, lib, checkpatch, binfmt, kallsyms, ramfs,
init, codafs, nilfs2, hfs, crash_dump, signals, seq_file, fork,
sysvfs, kcov, gdb, resource, selftests, and ipc"
* emailed patches from Andrew Morton <akpm@linux-foundation.org>: (87 commits)
ipc/ipc_sysctl.c: remove fallback for !CONFIG_PROC_SYSCTL
ipc: check checkpoint_restore_ns_capable() to modify C/R proc files
selftests/kselftest/runner/run_one(): allow running non-executable files
virtio-mem: disallow mapping virtio-mem memory via /dev/mem
kernel/resource: disallow access to exclusive system RAM regions
kernel/resource: clean up and optimize iomem_is_exclusive()
scripts/gdb: handle split debug for vmlinux
kcov: replace local_irq_save() with a local_lock_t
kcov: avoid enable+disable interrupts if !in_task()
kcov: allocate per-CPU memory on the relevant node
Documentation/kcov: define `ip' in the example
Documentation/kcov: include types.h in the example
sysv: use BUILD_BUG_ON instead of runtime check
kernel/fork.c: unshare(): use swap() to make code cleaner
seq_file: fix passing wrong private data
seq_file: move seq_escape() to a header
signal: remove duplicate include in signal.h
crash_dump: remove duplicate include in crash_dump.h
crash_dump: fix boolreturn.cocci warning
hfs/hfsplus: use WARN_ON for sanity check
...
Patch series "sections: Unify kernel sections range check and use", v4.
There are three head files(kallsyms.h, kernel.h and sections.h) which
include the kernel sections range check, let's make some cleanup and unify
them.
1. cleanup arch specific text/data check and fix address boundary check
in kallsyms.h
2. make all the basic/core kernel range check function into sections.h
3. update all the callers, and use the helper in sections.h to simplify
the code
After this series, we have 5 APIs about kernel sections range check in
sections.h
* is_kernel_rodata() --- already in sections.h
* is_kernel_core_data() --- come from core_kernel_data() in kernel.h
* is_kernel_inittext() --- come from kernel.h and kallsyms.h
* __is_kernel_text() --- add new internal helper
* __is_kernel() --- add new internal helper
Note: For the last two helpers, people should not use directly, consider to
use corresponding function in kallsyms.h.
This patch (of 11):
Remove arch specific text and data check after commit 4ba66a9760 ("arch:
remove blackfin port"), no need arch-specific text/data check.
Link: https://lkml.kernel.org/r/20210930071143.63410-1-wangkefeng.wang@huawei.com
Link: https://lkml.kernel.org/r/20210930071143.63410-2-wangkefeng.wang@huawei.com
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Merge misc updates from Andrew Morton:
"257 patches.
Subsystems affected by this patch series: scripts, ocfs2, vfs, and
mm (slab-generic, slab, slub, kconfig, dax, kasan, debug, pagecache,
gup, swap, memcg, pagemap, mprotect, mremap, iomap, tracing, vmalloc,
pagealloc, memory-failure, hugetlb, userfaultfd, vmscan, tools,
memblock, oom-kill, hugetlbfs, migration, thp, readahead, nommu, ksm,
vmstat, madvise, memory-hotplug, rmap, zsmalloc, highmem, zram,
cleanups, kfence, and damon)"
* emailed patches from Andrew Morton <akpm@linux-foundation.org>: (257 commits)
mm/damon: remove return value from before_terminate callback
mm/damon: fix a few spelling mistakes in comments and a pr_debug message
mm/damon: simplify stop mechanism
Docs/admin-guide/mm/pagemap: wordsmith page flags descriptions
Docs/admin-guide/mm/damon/start: simplify the content
Docs/admin-guide/mm/damon/start: fix a wrong link
Docs/admin-guide/mm/damon/start: fix wrong example commands
mm/damon/dbgfs: add adaptive_targets list check before enable monitor_on
mm/damon: remove unnecessary variable initialization
Documentation/admin-guide/mm/damon: add a document for DAMON_RECLAIM
mm/damon: introduce DAMON-based Reclamation (DAMON_RECLAIM)
selftests/damon: support watermarks
mm/damon/dbgfs: support watermarks
mm/damon/schemes: activate schemes based on a watermarks mechanism
tools/selftests/damon: update for regions prioritization of schemes
mm/damon/dbgfs: support prioritization weights
mm/damon/vaddr,paddr: support pageout prioritization
mm/damon/schemes: prioritize regions within the quotas
mm/damon/selftests: support schemes quotas
mm/damon/dbgfs: support quotas of schemes
...
Commit 7a5da02de8 ("locking/lockdep: check for freed initmem in
static_obj()") added arch_is_kernel_initmem_freed() which is supposed to
report whether an object is part of already freed init memory.
For the time being, the generic version of
arch_is_kernel_initmem_freed() always reports 'false', allthough
free_initmem() is generically called on all architectures.
Therefore, change the generic version of arch_is_kernel_initmem_freed()
to check whether free_initmem() has been called. If so, then check if a
given address falls into init memory.
To ease the use of system_state, move it out of line into its only
caller which is lockdep.c
Link: https://lkml.kernel.org/r/1d40783e676e07858be97d881f449ee7ea8adfb1.1633001016.git.christophe.leroy@csgroup.eu
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This pull request contains the following branches:
fixes.2021.10.07a: Miscellaneous fixes.
scftorture.2021.09.16a: smp_call_function torture-test updates, most
notably better checking of module parameters.
tasks.2021.09.15a: Tasks-trace RCU updates that fix a number of rare
but important race-condition bugs.
torture.2021.09.13b: Other torture-test updates, most notably
better checking of module parameters. In addition, rcutorture
may now be run on CONFIG_PREEMPT_RT kernels.
torturescript.2021.09.16a: Torture-test scripting updates, most notably
specifying the new CONFIG_KCSAN_STRICT kconfig option rather
than maintaining an ever-changing list of individual KCSAN
kconfig options.
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Merge tag 'rcu.2021.11.01a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu
Pull RCU updates from Paul McKenney:
- Miscellaneous fixes
- Torture-test updates for smp_call_function(), most notably improved
checking of module parameters.
- Tasks-trace RCU updates that fix a number of rare but important
race-condition bugs.
- Other torture-test updates, most notably better checking of module
parameters. In addition, rcutorture may once again be run on
CONFIG_PREEMPT_RT kernels.
- Torture-test scripting updates, most notably specifying the new
CONFIG_KCSAN_STRICT kconfig option rather than maintaining an
ever-changing list of individual KCSAN kconfig options.
* tag 'rcu.2021.11.01a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (46 commits)
rcu: Fix rcu_dynticks_curr_cpu_in_eqs() vs noinstr
rcu: Always inline rcu_dynticks_task*_{enter,exit}()
torture: Make kvm-remote.sh print size of downloaded tarball
torture: Allot 1G of memory for scftorture runs
tools/rcu: Add an extract-stall script
scftorture: Warn on individual scf_torture_init() error conditions
scftorture: Count reschedule IPIs
scftorture: Account for weight_resched when checking for all zeroes
scftorture: Shut down if nonsensical arguments given
scftorture: Allow zero weight to exclude an smp_call_function*() category
rcu: Avoid unneeded function call in rcu_read_unlock()
rcu-tasks: Update comments to cond_resched_tasks_rcu_qs()
rcu-tasks: Fix IPI failure handling in trc_wait_for_one_reader
rcu-tasks: Fix read-side primitives comment for call_rcu_tasks_trace
rcu-tasks: Clarify read side section info for rcu_tasks_rude GP primitives
rcu-tasks: Correct comparisons for CPU numbers in show_stalled_task_trace
rcu-tasks: Correct firstreport usage in check_all_holdout_tasks_trace
rcu-tasks: Fix s/rcu_add_holdout/trc_add_holdout/ typo in comment
rcu-tasks: Move RTGS_WAIT_CBS to beginning of rcu_tasks_kthread() loop
rcu-tasks: Fix s/instruction/instructions/ typo in comment
...
- Improve retpoline code patching by separating it from alternatives which
reduces memory footprint and allows to do better optimizations in the
actual runtime patching.
- Add proper retpoline support for x86/BPF
- Address noinstr warnings in x86/kvm, lockdep and paravirtualization code
- Add support to handle pv_opsindirect calls in the noinstr analysis
- Classify symbols upfront and cache the result to avoid redundant
str*cmp() invocations.
- Add a CFI hash to reduce memory consumption which also reduces runtime
on a allyesconfig by ~50%
- Adjust XEN code to make objtool handling more robust and as a side
effect to prevent text fragmentation due to placement of the hypercall
page.
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Merge tag 'objtool-core-2021-10-31' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull objtool updates from Thomas Gleixner:
- Improve retpoline code patching by separating it from alternatives
which reduces memory footprint and allows to do better optimizations
in the actual runtime patching.
- Add proper retpoline support for x86/BPF
- Address noinstr warnings in x86/kvm, lockdep and paravirtualization
code
- Add support to handle pv_opsindirect calls in the noinstr analysis
- Classify symbols upfront and cache the result to avoid redundant
str*cmp() invocations.
- Add a CFI hash to reduce memory consumption which also reduces
runtime on a allyesconfig by ~50%
- Adjust XEN code to make objtool handling more robust and as a side
effect to prevent text fragmentation due to placement of the
hypercall page.
* tag 'objtool-core-2021-10-31' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (41 commits)
bpf,x86: Respect X86_FEATURE_RETPOLINE*
bpf,x86: Simplify computing label offsets
x86,bugs: Unconditionally allow spectre_v2=retpoline,amd
x86/alternative: Add debug prints to apply_retpolines()
x86/alternative: Try inline spectre_v2=retpoline,amd
x86/alternative: Handle Jcc __x86_indirect_thunk_\reg
x86/alternative: Implement .retpoline_sites support
x86/retpoline: Create a retpoline thunk array
x86/retpoline: Move the retpoline thunk declarations to nospec-branch.h
x86/asm: Fixup odd GEN-for-each-reg.h usage
x86/asm: Fix register order
x86/retpoline: Remove unused replacement symbols
objtool,x86: Replace alternatives with .retpoline_sites
objtool: Shrink struct instruction
objtool: Explicitly avoid self modifying code in .altinstr_replacement
objtool: Classify symbols
objtool: Support pv_opsindirect calls for noinstr
x86/xen: Rework the xen_{cpu,irq,mmu}_opsarrays
x86/xen: Mark xen_force_evtchn_callback() noinstr
x86/xen: Make irq_disable() noinstr
...
parisc, ia64 and powerpc32 are the only remaining architectures that
provide custom arch_{spin,read,write}_lock_flags() functions, which are
meant to re-enable interrupts while waiting for a spinlock.
However, none of these can actually run into this codepath, because
it is only called on architectures without CONFIG_GENERIC_LOCKBREAK,
or when CONFIG_DEBUG_LOCK_ALLOC is set without CONFIG_LOCKDEP, and none
of those combinations are possible on the three architectures.
Going back in the git history, it appears that arch/mn10300 may have
been able to run into this code path, but there is a good chance that
it never worked. On the architectures that still exist, it was
already impossible to hit back in 2008 after the introduction of
CONFIG_GENERIC_LOCKBREAK, and possibly earlier.
As this is all dead code, just remove it and the helper functions built
around it. For arch/ia64, the inline asm could be cleaned up, but
it seems safer to leave it untouched.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Helge Deller <deller@gmx.de> # parisc
Link: https://lore.kernel.org/r/20211022120058.1031690-1-arnd@kernel.org
After the commit 617f3ef951 ("locking/rwsem: Remove reader
optimistic spinning"), reader doesn't support optimistic spinning
anymore, there is no need meet the condition which OSQ is empty.
BTW, add an unlikely() for the max reader wakeup check in the loop.
Signed-off-by: Yanfei Xu <yanfei.xu@windriver.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20211013134154.1085649-4-yanfei.xu@windriver.com
preempt_disable/enable() is equal to RCU read-side crital section, and
the spinning codes in mutex and rwsem could ensure that the preemption
is disabled. So let's remove the unnecessary rcu_read_lock/unlock for
saving some cycles in hot codes.
Signed-off-by: Yanfei Xu <yanfei.xu@windriver.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20211013134154.1085649-2-yanfei.xu@windriver.com
The spinning region rwsem_spin_on_owner() should not be preempted,
however the rwsem_down_write_slowpath() invokes it and don't disable
preemption. Fix it by adding a pair of preempt_disable/enable().
Signed-off-by: Yanfei Xu <yanfei.xu@windriver.com>
[peterz: Fix CONFIG_RWSEM_SPIN_ON_OWNER=n build]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20211013134154.1085649-3-yanfei.xu@windriver.com
Instead of a full barrier around the Rmw insn, micro-optimize
for weakly ordered archs such that we only provide the required
ACQUIRE semantics when taking the read lock.
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://lkml.kernel.org/r/20210920052031.54220-2-dave@stgolabs.net
The rw_semaphore and rwlock_t implementation both wake the waiter while
holding the rt_mutex_base::wait_lock acquired.
This can be optimized by waking the waiter lockless outside of the
locked section to avoid a needless contention on the
rt_mutex_base::wait_lock lock.
Extend rt_mutex_wake_q_add() to also accept task and state and use it in
__rwbase_read_unlock().
Suggested-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210928150006.597310-3-bigeasy@linutronix.de
rt_mutex_wake_q_add() needs to need to distiguish between sleeping
locks (TASK_RTLOCK_WAIT) and normal locks which use TASK_NORMAL to use
the proper wake mechanism.
Instead of checking for != TASK_NORMAL make it more robust and check
explicit for TASK_RTLOCK_WAIT which is the reason why a different wake
mechanism is used.
No functional change.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210928150006.597310-2-bigeasy@linutronix.de
The general rule that rcu_read_lock() held sections cannot voluntary sleep
does apply even on RT kernels. Though the substitution of spin/rw locks on
RT enabled kernels has to be exempt from that rule. On !RT a spin_lock()
can obviously nest inside a RCU read side critical section as the lock
acquisition is not going to block, but on RT this is not longer the case
due to the 'sleeping' spinlock substitution.
The RT patches contained a cheap hack to ignore the RCU nesting depth in
might_sleep() checks, which was a pragmatic but incorrect workaround.
Instead of generally ignoring the RCU nesting depth in __might_sleep() and
__might_resched() checks, pass the rcu_preempt_depth() via the offsets
argument to __might_resched() from spin/read/write_lock() which makes the
checks work correctly even in RCU read side critical sections.
The actual blocking on such a substituted lock within a RCU read side
critical section is already handled correctly in __schedule() by treating
it as a "preemption" of the RCU read side critical section.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210923165358.368305497@linutronix.de
__might_sleep() vs. ___might_sleep() is hard to distinguish. Aside of that
the three underscore variant is exposed to provide a checkpoint for
rescheduling points which are distinct from blocking points.
They are semantically a preemption point which means that scheduling is
state preserving. A real blocking operation, e.g. mutex_lock(), wait*(),
which cannot preserve a task state which is not equal to RUNNING.
While technically blocking on a "sleeping" spinlock in RT enabled kernels
falls into the voluntary scheduling category because it has to wait until
the contended spin/rw lock becomes available, the RT lock substitution code
can semantically be mapped to a voluntary preemption because the RT lock
substitution code and the scheduler are providing mechanisms to preserve
the task state and to take regular non-lock related wakeups into account.
Rename ___might_sleep() to __might_resched() to make the distinction of
these functions clear.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210923165357.928693482@linutronix.de
Clang warns:
kernel/locking/test-ww_mutex.c:138:7: error: variable 'ret' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
if (!ww_mutex_trylock(&mutex, &ctx)) {
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
kernel/locking/test-ww_mutex.c:172:9: note: uninitialized use occurs here
return ret;
^~~
kernel/locking/test-ww_mutex.c:138:3: note: remove the 'if' if its condition is always false
if (!ww_mutex_trylock(&mutex, &ctx)) {
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
kernel/locking/test-ww_mutex.c:125:9: note: initialize the variable 'ret' to silence this warning
int ret;
^
= 0
1 error generated.
Assign !ww_mutex_trylock(...) to ret so that it is always initialized.
Fixes: 12235da8c8 ("kernel/locking: Add context to ww_mutex_trylock()")
Reported-by: "kernelci.org bot" <bot@kernelci.org>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20210922145822.3935141-1-nathan@kernel.org
Comments in wait-type checks be improved by mentioning the
PREEPT_RT kernel configure option.
Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lkml.kernel.org/r/20210811025920.20751-1-zhouzhouyi@gmail.com
lock_is_held_type(, 1) detects acquired read locks. It only recognized
locks acquired with lock_acquire_shared(). Read locks acquired with
lock_acquire_shared_recursive() are not recognized because a `2' is
stored as the read value.
Rework the check to additionally recognise lock's read value one and two
as a read held lock.
Fixes: e918188611 ("locking: More accurate annotations for read_lock()")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Boqun Feng <boqun.feng@gmail.com>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://lkml.kernel.org/r/20210903084001.lblecrvz4esl4mrr@linutronix.de
i915 will soon gain an eviction path that trylock a whole lot of locks
for eviction, getting dmesg failures like below:
BUG: MAX_LOCK_DEPTH too low!
turning off the locking correctness validator.
depth: 48 max: 48!
48 locks held by i915_selftest/5776:
#0: ffff888101a79240 (&dev->mutex){....}-{3:3}, at: __driver_attach+0x88/0x160
#1: ffffc900009778c0 (reservation_ww_class_acquire){+.+.}-{0:0}, at: i915_vma_pin.constprop.63+0x39/0x1b0 [i915]
#2: ffff88800cf74de8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_vma_pin.constprop.63+0x5f/0x1b0 [i915]
#3: ffff88810c7f9e38 (&vm->mutex/1){+.+.}-{3:3}, at: i915_vma_pin_ww+0x1c4/0x9d0 [i915]
#4: ffff88810bad5768 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915]
#5: ffff88810bad60e8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915]
...
#46: ffff88811964d768 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915]
#47: ffff88811964e0e8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915]
INFO: lockdep is turned off.
Fixing eviction to nest into ww_class_acquire is a high priority, but
it requires a rework of the entire driver, which can only be done one
step at a time.
As an intermediate solution, add an acquire context to
ww_mutex_trylock, which allows us to do proper nesting annotations on
the trylocks, making the above lockdep splat disappear.
This is also useful in regulator_lock_nested, which may avoid dropping
regulator_nesting_mutex in the uncontended path, so use it there.
TTM may be another user for this, where we could lock a buffer in a
fastpath with list locks held, without dropping all locks we hold.
[peterz: rework actual ww_mutex_trylock() implementations]
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/YUBGPdDDjKlxAuXJ@hirez.programming.kicks-ass.net
Readers of rwbase can lock and unlock without taking any inner lock, if
that happens, we need the ordering provided by atomic operations to
satisfy the ordering semantics of lock/unlock. Without that, considering
the follow case:
{ X = 0 initially }
CPU 0 CPU 1
===== =====
rt_write_lock();
X = 1
rt_write_unlock():
atomic_add(READER_BIAS - WRITER_BIAS, ->readers);
// ->readers is READER_BIAS.
rt_read_lock():
if ((r = atomic_read(->readers)) < 0) // True
atomic_try_cmpxchg(->readers, r, r + 1); // succeed.
<acquire the read lock via fast path>
r1 = X; // r1 may be 0, because nothing prevent the reordering
// of "X=1" and atomic_add() on CPU 1.
Therefore audit every usage of atomic operations that may happen in a
fast path, and add necessary barriers.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20210909110203.953991276@infradead.org
The code in rwbase_write_lock() is a little non-obvious vs the
read+set 'trylock', extract the sequence into a helper function to
clarify the code.
This also provides a single site to fix fast-path ordering.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/YUCq3L+u44NDieEJ@hirez.programming.kicks-ass.net
Noticed while looking at the readers race.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lkml.kernel.org/r/20210909110203.828203010@infradead.org
When running locktorture as a module, any lock_torture_init() issues will be
reflected in the error code from modprobe or insmod, as the case may be.
However, these error codes are not available when running locktorture
built-in, for example, when using the kvm.sh script. This commit
therefore adds WARN_ON_ONCE() to allow distinguishing lock_torture_init()
errors when running locktorture built-in.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Dan reported that rt_mutex_adjust_prio_chain() can be called with
.orig_waiter == NULL however commit a055fcc132 ("locking/rtmutex: Return
success on deadlock for ww_mutex waiters") unconditionally dereferences it.
Since both call-sites that have .orig_waiter == NULL don't care for the
return value, simply disable the deadlock squash by adding the NULL check.
Notably, both callers use the deadlock condition as a termination condition
for the iteration; once detected, it is sure that (de)boosting is done.
Arguably step [3] would be a more natural termination point, but it's
dubious whether adding a third deadlock detection state would improve the
code.
Fixes: a055fcc132 ("locking/rtmutex: Return success on deadlock for ww_mutex waiters")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/YS9La56fHMiCCo75@hirez.programming.kicks-ass.net
The regular pile:
- A few improvements to the mutex code
- Documentation updates for atomics to clarify the difference between
cmpxchg() and try_cmpxchg() and to explain the forward progress
expectations.
- Simplification of the atomics fallback generator
- The addition of arch_atomic_long*() variants and generic arch_*()
bitops based on them.
- Add the missing might_sleep() invocations to the down*() operations of
semaphores.
The PREEMPT_RT locking core:
- Scheduler updates to support the state preserving mechanism for
'sleeping' spin- and rwlocks on RT. This mechanism is carefully
preserving the state of the task when blocking on a 'sleeping' spin- or
rwlock and takes regular wake-ups targeted at the same task into
account. The preserved or updated (via a regular wakeup) state is
restored when the lock has been acquired.
- Restructuring of the rtmutex code so it can be utilized and extended
for the RT specific lock variants.
- Restructuring of the ww_mutex code to allow sharing of the ww_mutex
specific functionality for rtmutex based ww_mutexes.
- Header file disentangling to allow substitution of the regular lock
implementations with the PREEMPT_RT variants without creating an
unmaintainable #ifdef mess.
- Shared base code for the PREEMPT_RT specific rw_semaphore and rwlock
implementations. Contrary to the regular rw_semaphores and rwlocks the
PREEMPT_RT implementation is writer unfair because it is infeasible to
do priority inheritance on multiple readers. Experience over the years
has shown that real-time workloads are not the typical workloads which
are sensitive to writer starvation. The alternative solution would be
to allow only a single reader which has been tried and discarded as it
is a major bottleneck especially for mmap_sem. Aside of that many of
the writer starvation critical usage sites have been converted to a
writer side mutex/spinlock and RCU read side protections in the past
decade so that the issue is less prominent than it used to be.
- The actual rtmutex based lock substitutions for PREEMPT_RT enabled
kernels which affect mutex, ww_mutex, rw_semaphore, spinlock_t and
rwlock_t. The spin/rw_lock*() functions disable migration across the
critical section to preserve the existing semantics vs. per CPU
variables.
- Rework of the futex REQUEUE_PI mechanism to handle the case of early
wake-ups which interleave with a re-queue operation to prevent the
situation that a task would be blocked on both the rtmutex associated
to the outer futex and the rtmutex based hash bucket spinlock.
While this situation cannot happen on !RT enabled kernels the changes
make the underlying concurrency problems easier to understand in
general. As a result the difference between !RT and RT kernels is
reduced to the handling of waiting for the critical section. !RT
kernels simply spin-wait as before and RT kernels utilize rcu_wait().
- The substitution of local_lock for PREEMPT_RT with a spinlock which
protects the critical section while staying preemptible. The CPU
locality is established by disabling migration.
The underlying concepts of this code have been in use in PREEMPT_RT for
way more than a decade. The code has been refactored several times over
the years and this final incarnation has been optimized once again to be
as non-intrusive as possible, i.e. the RT specific parts are mostly
isolated.
It has been extensively tested in the 5.14-rt patch series and it has
been verified that !RT kernels are not affected by these changes.
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Merge tag 'locking-core-2021-08-30' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking and atomics updates from Thomas Gleixner:
"The regular pile:
- A few improvements to the mutex code
- Documentation updates for atomics to clarify the difference between
cmpxchg() and try_cmpxchg() and to explain the forward progress
expectations.
- Simplification of the atomics fallback generator
- The addition of arch_atomic_long*() variants and generic arch_*()
bitops based on them.
- Add the missing might_sleep() invocations to the down*() operations
of semaphores.
The PREEMPT_RT locking core:
- Scheduler updates to support the state preserving mechanism for
'sleeping' spin- and rwlocks on RT.
This mechanism is carefully preserving the state of the task when
blocking on a 'sleeping' spin- or rwlock and takes regular wake-ups
targeted at the same task into account. The preserved or updated
(via a regular wakeup) state is restored when the lock has been
acquired.
- Restructuring of the rtmutex code so it can be utilized and
extended for the RT specific lock variants.
- Restructuring of the ww_mutex code to allow sharing of the ww_mutex
specific functionality for rtmutex based ww_mutexes.
- Header file disentangling to allow substitution of the regular lock
implementations with the PREEMPT_RT variants without creating an
unmaintainable #ifdef mess.
- Shared base code for the PREEMPT_RT specific rw_semaphore and
rwlock implementations.
Contrary to the regular rw_semaphores and rwlocks the PREEMPT_RT
implementation is writer unfair because it is infeasible to do
priority inheritance on multiple readers. Experience over the years
has shown that real-time workloads are not the typical workloads
which are sensitive to writer starvation.
The alternative solution would be to allow only a single reader
which has been tried and discarded as it is a major bottleneck
especially for mmap_sem. Aside of that many of the writer
starvation critical usage sites have been converted to a writer
side mutex/spinlock and RCU read side protections in the past
decade so that the issue is less prominent than it used to be.
- The actual rtmutex based lock substitutions for PREEMPT_RT enabled
kernels which affect mutex, ww_mutex, rw_semaphore, spinlock_t and
rwlock_t. The spin/rw_lock*() functions disable migration across
the critical section to preserve the existing semantics vs per-CPU
variables.
- Rework of the futex REQUEUE_PI mechanism to handle the case of
early wake-ups which interleave with a re-queue operation to
prevent the situation that a task would be blocked on both the
rtmutex associated to the outer futex and the rtmutex based hash
bucket spinlock.
While this situation cannot happen on !RT enabled kernels the
changes make the underlying concurrency problems easier to
understand in general. As a result the difference between !RT and
RT kernels is reduced to the handling of waiting for the critical
section. !RT kernels simply spin-wait as before and RT kernels
utilize rcu_wait().
- The substitution of local_lock for PREEMPT_RT with a spinlock which
protects the critical section while staying preemptible. The CPU
locality is established by disabling migration.
The underlying concepts of this code have been in use in PREEMPT_RT for
way more than a decade. The code has been refactored several times over
the years and this final incarnation has been optimized once again to be
as non-intrusive as possible, i.e. the RT specific parts are mostly
isolated.
It has been extensively tested in the 5.14-rt patch series and it has
been verified that !RT kernels are not affected by these changes"
* tag 'locking-core-2021-08-30' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (92 commits)
locking/rtmutex: Return success on deadlock for ww_mutex waiters
locking/rtmutex: Prevent spurious EDEADLK return caused by ww_mutexes
locking/rtmutex: Dequeue waiter on ww_mutex deadlock
locking/rtmutex: Dont dereference waiter lockless
locking/semaphore: Add might_sleep() to down_*() family
locking/ww_mutex: Initialize waiter.ww_ctx properly
static_call: Update API documentation
locking/local_lock: Add PREEMPT_RT support
locking/spinlock/rt: Prepare for RT local_lock
locking/rtmutex: Add adaptive spinwait mechanism
locking/rtmutex: Implement equal priority lock stealing
preempt: Adjust PREEMPT_LOCK_OFFSET for RT
locking/rtmutex: Prevent lockdep false positive with PI futexes
futex: Prevent requeue_pi() lock nesting issue on RT
futex: Simplify handle_early_requeue_pi_wakeup()
futex: Reorder sanity checks in futex_requeue()
futex: Clarify comment in futex_requeue()
futex: Restructure futex_requeue()
futex: Correct the number of requeued waiters for PI
futex: Remove bogus condition for requeue PI
...
Pull RCU updates from Paul McKenney:
"RCU changes for this cycle were:
- Documentation updates
- Miscellaneous fixes
- Offloaded-callbacks updates
- Updates to the nolibc library
- Tasks-RCU updates
- In-kernel torture-test updates
- Torture-test scripting, perhaps most notably the pinning of
torture-test guest OSes so as to force differences in memory
latency. For example, in a two-socket system, a four-CPU guest OS
will have one pair of its CPUs pinned to threads in a single core
on one socket and the other pair pinned to threads in a single core
on the other socket. This approach proved able to force race
conditions that earlier testing missed. Some of these race
conditions are still being tracked down"
* 'core-rcu.2021.08.28a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (61 commits)
torture: Replace deprecated CPU-hotplug functions.
rcu: Replace deprecated CPU-hotplug functions
rcu: Print human-readable message for schedule() in RCU reader
rcu: Explain why rcu_all_qs() is a stub in preemptible TREE RCU
rcu: Use per_cpu_ptr to get the pointer of per_cpu variable
rcu: Remove useless "ret" update in rcu_gp_fqs_loop()
rcu: Mark accesses in tree_stall.h
rcu: Make rcu_gp_init() and rcu_gp_fqs_loop noinline to conserve stack
rcu: Mark lockless ->qsmask read in rcu_check_boost_fail()
srcutiny: Mark read-side data races
rcu: Start timing stall repetitions after warning complete
rcu: Do not disable GP stall detection in rcu_cpu_stall_reset()
rcu/tree: Handle VM stoppage in stall detection
rculist: Unify documentation about missing list_empty_rcu()
rcu: Mark accesses to ->rcu_read_lock_nesting
rcu: Weaken ->dynticks accesses and updates
rcu: Remove special bit at the bottom of the ->dynticks counter
rcu: Fix stall-warning deadlock due to non-release of rcu_node ->lock
rcu: Fix to include first blocked task in stall warning
torture: Make kvm-test-1-run-qemu.sh check for reboot loops
...
ww_mutexes can legitimately cause a deadlock situation in the lock graph
which is resolved afterwards by the wait/wound mechanics. The rtmutex chain
walk can detect such a deadlock and returns EDEADLK which in turn skips the
wait/wound mechanism and returns EDEADLK to the caller. That's wrong
because both lock chains might get EDEADLK or the wrong waiter would back
out.
Detect that situation and return 'success' in case that the waiter which
initiated the chain walk is a ww_mutex with context. This allows the
wait/wound mechanics to resolve the situation according to the rules.
[ tglx: Split it apart and added changelog ]
Reported-by: Sebastian Siewior <bigeasy@linutronix.de>
Fixes: add461325e ("locking/rtmutex: Extend the rtmutex core to support ww_mutex")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/YSeWjCHoK4v5OcOt@hirez.programming.kicks-ass.net
rtmutex based ww_mutexes can legitimately create a cycle in the lock graph
which can be observed by a blocker which didn't cause the problem:
P1: A, ww_A, ww_B
P2: ww_B, ww_A
P3: A
P3 might therefore be trapped in the ww_mutex induced cycle and run into
the lock depth limitation of rt_mutex_adjust_prio_chain() which returns
-EDEADLK to the caller.
Disable the deadlock detection walk when the chain walk observes a
ww_mutex to prevent this looping.
[ tglx: Split it apart and added changelog ]
Reported-by: Sebastian Siewior <bigeasy@linutronix.de>
Fixes: add461325e ("locking/rtmutex: Extend the rtmutex core to support ww_mutex")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/YSeWjCHoK4v5OcOt@hirez.programming.kicks-ass.net
The rt_mutex based ww_mutex variant queues the new waiter first in the
lock's rbtree before evaluating the ww_mutex specific conditions which
might decide that the waiter should back out. This check and conditional
exit happens before the waiter is enqueued into the PI chain.
The failure handling at the call site assumes that the waiter, if it is the
top most waiter on the lock, is queued in the PI chain and then proceeds to
adjust the unmodified PI chain, which results in RB tree corruption.
Dequeue the waiter from the lock waiter list in the ww_mutex error exit
path to prevent this.
Fixes: add461325e ("locking/rtmutex: Extend the rtmutex core to support ww_mutex")
Reported-by: Sebastian Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210825102454.042280541@linutronix.de
The new rt_mutex_spin_on_onwer() loop checks whether the spinning waiter is
still the top waiter on the lock by utilizing rt_mutex_top_waiter(), which
is broken because that function contains a sanity check which dereferences
the top waiter pointer to check whether the waiter belongs to the
lock. That's wrong in the lockless spinwait case:
CPU 0 CPU 1
rt_mutex_lock(lock) rt_mutex_lock(lock);
queue(waiter0)
waiter0 == rt_mutex_top_waiter(lock)
rt_mutex_spin_on_onwer(lock, waiter0) { queue(waiter1)
waiter1 == rt_mutex_top_waiter(lock)
...
top_waiter = rt_mutex_top_waiter(lock)
leftmost = rb_first_cached(&lock->waiters);
-> signal
dequeue(waiter1)
destroy(waiter1)
w = rb_entry(leftmost, ....)
BUG_ON(w->lock != lock) <- UAF
The BUG_ON() is correct for the case where the caller holds lock->wait_lock
which guarantees that the leftmost waiter entry cannot vanish. For the
lockless spinwait case it's broken.
Create a new helper function which avoids the pointer dereference and just
compares the leftmost entry pointer with current's waiter pointer to
validate that currrent is still elegible for spinning.
Fixes: 992caf7f17 ("locking/rtmutex: Add adaptive spinwait mechanism")
Reported-by: Sebastian Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210825102453.981720644@linutronix.de
Semaphore is sleeping lock. Add might_sleep() to down*() family
(with exception of down_trylock()) to detect atomic context sleep.
Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20210809021215.19991-1-nixiaoming@huawei.com
The consolidation of the debug code for mutex waiter intialization sets
waiter::ww_ctx to a poison value unconditionally. For regular mutexes this
is intended to catch the case where waiter_ww_ctx is dereferenced
accidentally.
For ww_mutex the poison value has to be overwritten either with a context
pointer or NULL for ww_mutexes without context.
The rework broke this as it made the store conditional on the context
pointer instead of the argument which signals whether ww_mutex code should
be compiled in or optiized out. As a result waiter::ww_ctx ends up with the
poison pointer for contextless ww_mutexes which causes a later dereference of
the poison pointer because it is != NULL.
Use the build argument instead so for ww_mutex the poison value is always
overwritten.
Fixes: c0afb0ffc0 ("locking/ww_mutex: Gather mutex_waiter initialization")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210819193030.zpwrpvvrmy7xxxiy@linutronix.de
Add the static and runtime initializer mechanics to support the RT variant
of local_lock, which requires the lock type in the lockdep map to be set
to LD_LOCK_PERCPU.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211305.967526724@linutronix.de
Going to sleep when locks are contended can be quite inefficient when the
contention time is short and the lock owner is running on a different CPU.
The MCS mechanism cannot be used because MCS is strictly FIFO ordered while
for rtmutex based locks the waiter ordering is priority based.
Provide a simple adaptive spinwait mechanism which currently restricts the
spinning to the top priority waiter.
[ tglx: Provide a contemporary changelog, extended it to all rtmutex based
locks and updated it to match the other spin on owner implementations ]
Originally-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211305.912050691@linutronix.de
The current logic only allows lock stealing to occur if the current task is
of higher priority than the pending owner.
Significant throughput improvements can be gained by allowing the lock
stealing to include tasks of equal priority when the contended lock is a
spin_lock or a rw_lock and the tasks are not in a RT scheduling task.
The assumption was that the system will make faster progress by allowing
the task already on the CPU to take the lock rather than waiting for the
system to wake up a different task.
This does add a degree of unfairness, but in reality no negative side
effects have been observed in the many years that this has been used in the
RT kernel.
[ tglx: Refactored and rewritten several times by Steve Rostedt, Sebastian
Siewior and myself ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211305.857240222@linutronix.de
On PREEMPT_RT the futex hashbucket spinlock becomes 'sleeping' and rtmutex
based. That causes a lockdep false positive because some of the futex
functions invoke spin_unlock(&hb->lock) with the wait_lock of the rtmutex
associated to the pi_futex held. spin_unlock() in turn takes wait_lock of
the rtmutex on which the spinlock is based which makes lockdep notice a
lock recursion.
Give the futex/rtmutex wait_lock a separate key.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211305.750701219@linutronix.de
Add the necessary defines, helpers and API functions for replacing struct mutex on
a PREEMPT_RT enabled kernel with an rtmutex based variant.
No functional change when CONFIG_PREEMPT_RT=n
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211305.081517417@linutronix.de
Add the actual ww_mutex API functions which replace the mutex based variant
on RT enabled kernels.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211305.024057938@linutronix.de
Add a ww acquire context pointer to the waiter and various functions and
add the ww_mutex related invocations to the proper spots in the locking
code, similar to the mutex based variant.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.966139174@linutronix.de
Provide the defines for RT mutex based ww_mutexes and fix up the debug logic
so it's either enabled by DEBUG_MUTEXES or DEBUG_RT_MUTEXES on RT kernels.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.908012566@linutronix.de
RT mutex based ww_mutexes cannot order based on timestamps. They have to
order based on priority. Add the necessary decision logic.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.847536630@linutronix.de
Provide the type defines and the helper inlines for rtmutex based ww_mutexes.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.790760545@linutronix.de
Accessing the internal wait_lock of mutex and rtmutex is slightly
different. Provide helper functions for that.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.734635961@linutronix.de
Some ww_mutex helper functions use pointers for the underlying mutex and
mutex_waiter. The upcoming rtmutex based implementation needs to share
these functions. Add and use defines for the types and replace the direct
types in the affected functions.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.678720245@linutronix.de
Move the mutex related access from various ww_mutex functions into helper
functions so they can be substituted for rtmutex based ww_mutex later.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.622477030@linutronix.de
The upcoming rtmutex based ww_mutex needs a different handling for
enqueueing a waiter. Split it out into a helper function.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.566318143@linutronix.de
Split out the waiter iteration functions so they can be substituted for a
rtmutex based ww_mutex later.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.509186185@linutronix.de
None of these functions will be on the stack when blocking in
schedule(), hence __sched is not needed.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.453235952@linutronix.de
Split the W/W mutex helper functions out into a separate header file, so
they can be shared with a rtmutex based variant later.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.396893399@linutronix.de
Split the ww related part out into a helper function so it can be reused
for a rtmutex based ww_mutex implementation.
[ mingo: Fixed bisection failure. ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.340166556@linutronix.de
The wait_lock of mutex is really a low level lock. Convert it to a
raw_spinlock like the wait_lock of rtmutex.
[ mingo: backmerged the test_lockup.c build fix by bigeasy. ]
Co-developed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.166863404@linutronix.de
Move the mutex waiter declaration from the public <linux/mutex.h> header
to the internal kernel/locking/mutex.h header.
There is no reason to expose it outside of the core code.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.054325923@linutronix.de
Having two header files which contain just the non-debug and debug variants
is mostly waste of disc space and has no real value. Stick the debug
variants into the common mutex.h file as counterpart to the stubs for the
non-debug case.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.995350521@linutronix.de
Ensure all !RT tasks have the same prio such that they end up in FIFO
order and aren't split up according to nice level.
The reason why nice levels were taken into account so far is historical. In
the early days of the rtmutex code it was done to give the PI boosting and
deboosting a larger coverage.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.938676930@linutronix.de
Similar to rw_semaphores, on RT the rwlock substitution is not writer fair,
because it's not feasible to have a writer inherit its priority to
multiple readers. Readers blocked on a writer follow the normal rules of
priority inheritance. Like RT spinlocks, RT rwlocks are state preserving
across the slow lock operations (contended case).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.882793524@linutronix.de
Provide the actual locking functions which make use of the general and
spinlock specific rtmutex code.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.826621464@linutronix.de
A simplified version of the rtmutex slowlock function, which neither handles
signals nor timeouts, and is careful about preserving the state of the
blocked task across the lock operation.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.770228446@linutronix.de
Guard the regular sleeping lock specific functionality, which is used for
rtmutex on non-RT enabled kernels and for mutex, rtmutex and semaphores on
RT enabled kernels so the code can be reused for the RT specific
implementation of spinlocks and rwlocks in a different compilation unit.
No functional change.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.311535693@linutronix.de
Add an rtlock_task pointer to rt_mutex_wake_q, which allows to handle the RT
specific wakeup for spin/rwlock waiters. The pointer is just consuming 4/8
bytes on the stack so it is provided unconditionaly to avoid #ifdeffery all
over the place.
This cannot use a regular wake_q, because a task can have concurrent wakeups which
would make it miss either lock or the regular wakeups, depending on what gets
queued first, unless task struct gains a separate wake_q_node for this, which
would be overkill, because there can only be a single task which gets woken
up in the spin/rw_lock unlock path.
No functional change for non-RT enabled kernels.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.253614678@linutronix.de
Prepare for the required state aware handling of waiter wakeups via wake_q
and switch the rtmutex code over to the rtmutex specific wrapper.
No functional change.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.197113263@linutronix.de
To handle the difference between wakeups for regular sleeping locks (mutex,
rtmutex, rw_semaphore) and the wakeups for 'sleeping' spin/rwlocks on
PREEMPT_RT enabled kernels correctly, it is required to provide a
wake_q_head construct which allows to keep them separate.
Provide a wrapper around wake_q_head and the required helpers, which will be
extended with the state handling later.
No functional change.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.139337655@linutronix.de
Regular sleeping locks like mutexes, rtmutexes and rw_semaphores are always
entering and leaving a blocking section with task state == TASK_RUNNING.
On a non-RT kernel spinlocks and rwlocks never affect the task state, but
on RT kernels these locks are converted to rtmutex based 'sleeping' locks.
So in case of contention the task goes to block, which requires to carefully
preserve the task state, and restore it after acquiring the lock taking
regular wakeups for the task into account, which happened while the task was
blocked. This state preserving is achieved by having a separate task state
for blocking on a RT spin/rwlock and a saved_state field in task_struct
along with careful handling of these wakeup scenarios in try_to_wake_up().
To avoid conditionals in the rtmutex code, store the wake state which has
to be used for waking a lock waiter in rt_mutex_waiter which allows to
handle the regular and RT spin/rwlocks by handing it to wake_up_state().
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.079800739@linutronix.de
The RT specific R/W semaphore implementation used to restrict the number of
readers to one, because a writer cannot block on multiple readers and
inherit its priority or budget.
The single reader restricting was painful in various ways:
- Performance bottleneck for multi-threaded applications in the page fault
path (mmap sem)
- Progress blocker for drivers which are carefully crafted to avoid the
potential reader/writer deadlock in mainline.
The analysis of the writer code paths shows that properly written RT tasks
should not take them. Syscalls like mmap(), file access which take mmap sem
write locked have unbound latencies, which are completely unrelated to mmap
sem. Other R/W sem users like graphics drivers are not suitable for RT tasks
either.
So there is little risk to hurt RT tasks when the RT rwsem implementation is
done in the following way:
- Allow concurrent readers
- Make writers block until the last reader left the critical section. This
blocking is not subject to priority/budget inheritance.
- Readers blocked on a writer inherit their priority/budget in the normal
way.
There is a drawback with this scheme: R/W semaphores become writer unfair
though the applications which have triggered writer starvation (mostly on
mmap_sem) in the past are not really the typical workloads running on a RT
system. So while it's unlikely to hit writer starvation, it's possible. If
there are unexpected workloads on RT systems triggering it, the problem
has to be revisited.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.016885947@linutronix.de
On PREEMPT_RT, rw_semaphores and rwlocks are substituted with an rtmutex and
a reader count. The implementation is writer unfair, as it is not feasible
to do priority inheritance on multiple readers, but experience has shown
that real-time workloads are not the typical workloads which are sensitive
to writer starvation.
The inner workings of rw_semaphores and rwlocks on RT are almost identical
except for the task state and signal handling. rw_semaphores are not state
preserving over a contention, they are expected to enter and leave with state
== TASK_RUNNING. rwlocks have a mechanism to preserve the state of the task
at entry and restore it after unblocking taking potential non-lock related
wakeups into account. rw_semaphores can also be subject to signal handling
interrupting a blocked state, while rwlocks ignore signals.
To avoid code duplication, provide a shared implementation which takes the
small difference vs. state and signals into account. The code is included
into the relevant rw_semaphore/rwlock base code and compiled for each use
case separately.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211302.957920571@linutronix.de
Split the inner workings of rt_mutex_slowlock() out into a separate
function, which can be reused by the upcoming RT lock substitutions,
e.g. for rw_semaphores.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211302.841971086@linutronix.de
RT builds substitutions for rwsem, mutex, spinlock and rwlock around
rtmutexes. Split the inner working out so each lock substitution can use
them with the appropriate lockdep annotations. This avoids having an extra
unused lockdep map in the wrapped rtmutex.
No functional change.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211302.784739994@linutronix.de
Prepare for reusing the inner functions of rtmutex for RT lock
substitutions: introduce kernel/locking/rtmutex_api.c and move
them there.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211302.726560996@linutronix.de
Allows the compiler to generate better code depending on the architecture.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211302.668958502@linutronix.de
Inlines are type-safe...
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211302.610830960@linutronix.de
RT mutexes belong to the LD_WAIT_SLEEP class. Make them so.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211302.031014562@linutronix.de
Currently, the lock_is_read_held variable is bool, so that a reader sets
it to true just after lock acquisition and then to false just before
lock release. This works in a rough statistical sense, but can result
in false negatives just after one of a pair of concurrent readers has
released the lock. This approach does have low overhead, but at the
expense of the setting to true potentially never leaving the reader's
store buffer, thus resulting in an unconditional false negative.
This commit therefore converts this variable to atomic_t and makes
the reader use atomic_inc() just after acquisition and atomic_dec()
just before release. This does increase overhead, but this increase is
negligible compared to the 10-microsecond lock hold time.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The lock_stress_stats structure's ->n_lock_fail and ->n_lock_acquired
fields are incremented and sampled locklessly using plain C-language
statements, which KCSAN objects to. This commit therefore marks the
statistics gathering with data_race() to flag the intent. While in
the area, this commit also reduces the number of accesses to the
->n_lock_acquired field, thus eliminating some possible check/use
confusion.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The 2nd parameter 'count' is not used in this function.
The places where the function is called are also modified.
Signed-off-by: xuyehan <xuyehan@xiaomi.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/1625547043-28103-1-git-send-email-yehanxu1@gmail.com
Yanfei reported that it is possible to loose HANDOFF when we race with
mutex_unlock() and end up setting HANDOFF on an unlocked mutex. At
that point anybody can steal it, losing HANDOFF in the process.
If this happens often enough, we can in fact starve the top waiter.
Solve this by folding the 'set HANDOFF' operation into the trylock
operation, such that either we acquire the lock, or it gets HANDOFF
set. This avoids having HANDOFF set on an unlocked mutex.
Reported-by: Yanfei Xu <yanfei.xu@windriver.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Reviewed-by: Yanfei Xu <yanfei.xu@windriver.com>
Link: https://lore.kernel.org/r/20210630154114.958507900@infradead.org
Yanfei reported that setting HANDOFF should not depend on recomputing
@first, only on @first state. Which would then give:
if (ww_ctx || !first)
first = __mutex_waiter_is_first(lock, &waiter);
if (first)
__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
But because 'ww_ctx || !first' is basically 'always' and the test for
first is relatively cheap, omit that first branch entirely.
Reported-by: Yanfei Xu <yanfei.xu@windriver.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Reviewed-by: Yanfei Xu <yanfei.xu@windriver.com>
Link: https://lore.kernel.org/r/20210630154114.896786297@infradead.org
Linus Torvalds