kernels, caused by a buggy factoring-out of existing code.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'timers-urgent-2023-09-02' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull timer fix from Ingo Molnar:
"Fix false positive 'softirq work is pending' messages on -rt kernels,
caused by a buggy factoring-out of existing code"
* tag 'timers-urgent-2023-09-02' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
tick/rcu: Fix false positive "softirq work is pending" messages
- Work from Carlos Bilbao to integrate rustdoc output into the generated
HTML documentation. This took some work to figure out how to do it
without slowing the docs build and without creating people who don't have
Rust installed, but Carlos got there.
- Move the loongarch and mips architecture documentation under
Documentation/arch/.
- Some more maintainer documentation from Jakub
...plus the usual assortment of updates, translations, and fixes.
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Merge tag 'docs-6.6' of git://git.lwn.net/linux
Pull documentation updates from Jonathan Corbet:
"Documentation work keeps chugging along; this includes:
- Work from Carlos Bilbao to integrate rustdoc output into the
generated HTML documentation. This took some work to figure out how
to do it without slowing the docs build and without creating people
who don't have Rust installed, but Carlos got there
- Move the loongarch and mips architecture documentation under
Documentation/arch/
- Some more maintainer documentation from Jakub
... plus the usual assortment of updates, translations, and fixes"
* tag 'docs-6.6' of git://git.lwn.net/linux: (56 commits)
Docu: genericirq.rst: fix irq-example
input: docs: pxrc: remove reference to phoenix-sim
Documentation: serial-console: Fix literal block marker
docs/mm: remove references to hmm_mirror ops and clean typos
docs/zh_CN: correct regi_chg(),regi_add() to region_chg(),region_add()
Documentation: Fix typos
Documentation/ABI: Fix typos
scripts: kernel-doc: fix macro handling in enums
scripts: kernel-doc: parse DEFINE_DMA_UNMAP_[ADDR|LEN]
Documentation: riscv: Update boot image header since EFI stub is supported
Documentation: riscv: Add early boot document
Documentation: arm: Add bootargs to the table of added DT parameters
docs: kernel-parameters: Refer to the correct bitmap function
doc: update params of memhp_default_state=
docs: Add book to process/kernel-docs.rst
docs: sparse: fix invalid link addresses
docs: vfs: clean up after the iterate() removal
docs: Add a section on surveys to the researcher guidelines
docs: move mips under arch
docs: move loongarch under arch
...
In commit 0345691b24 ("tick/rcu: Stop allowing RCU_SOFTIRQ in idle") the
new function report_idle_softirq() was created by breaking code out of the
existing can_stop_idle_tick() for kernels v5.18 and newer.
In doing so, the code essentially went from a one conditional:
if (a && b && c)
warn();
to a three conditional:
if (!a)
return;
if (!b)
return;
if (!c)
return;
warn();
But that conversion got the condition for the RT specific
local_bh_blocked() wrong. The original condition was:
!local_bh_blocked()
but the conversion failed to negate it so it ended up as:
if (!local_bh_blocked())
return false;
This issue lay dormant until another fixup for the same commit was added
in commit a7e282c777 ("tick/rcu: Fix bogus ratelimit condition").
This commit realized the ratelimit was essentially set to zero instead
of ten, and hence *no* softirq pending messages would ever be issued.
Once this commit was backported via linux-stable, both the v6.1 and v6.4
preempt-rt kernels started printing out 10 instances of this at boot:
NOHZ tick-stop error: local softirq work is pending, handler #80!!!
Remove the negation and return when local_bh_blocked() evaluates to true to
bring the correct behaviour back.
Fixes: 0345691b24 ("tick/rcu: Stop allowing RCU_SOFTIRQ in idle")
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Reviewed-by: Wen Yang <wenyang.linux@foxmail.com>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20230818200757.1808398-1-paul.gortmaker@windriver.com
This kunit update for Linux 6.6.rc1 consists of:
-- Adds support for running Rust documentation tests as KUnit tests
-- Makes init, str, sync, types doctests compilable/testable
-- Adds support for attributes API which include speed, modules
attributes, ability to filter and report attributes.
-- Adds support for marking tests slow using attributes API.
-- Adds attributes API documentation
-- Fixes to wild-memory-access bug in kunit_filter_suites() and
a possible memory leak in kunit_filter_suites()
-- Adds support for counting number of test suites in a module, list
action to kunit test modules, and test filtering on module tests.
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Merge tag 'linux-kselftest-kunit-6.6-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest
Pull kunit updates from Shuah Khan:
- add support for running Rust documentation tests as KUnit tests
- make init, str, sync, types doctests compilable/testable
- add support for attributes API which include speed, modules
attributes, ability to filter and report attributes
- add support for marking tests slow using attributes API
- add attributes API documentation
- fix a wild-memory-access bug in kunit_filter_suites() and a possible
memory leak in kunit_filter_suites()
- add support for counting number of test suites in a module, list
action to kunit test modules, and test filtering on module tests
* tag 'linux-kselftest-kunit-6.6-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest: (25 commits)
kunit: fix struct kunit_attr header
kunit: replace KUNIT_TRIGGER_STATIC_STUB maro with KUNIT_STATIC_STUB_REDIRECT
kunit: Allow kunit test modules to use test filtering
kunit: Make 'list' action available to kunit test modules
kunit: Report the count of test suites in a module
kunit: fix uninitialized variables bug in attributes filtering
kunit: fix possible memory leak in kunit_filter_suites()
kunit: fix wild-memory-access bug in kunit_filter_suites()
kunit: Add documentation of KUnit test attributes
kunit: add tests for filtering attributes
kunit: time: Mark test as slow using test attributes
kunit: memcpy: Mark tests as slow using test attributes
kunit: tool: Add command line interface to filter and report attributes
kunit: Add ability to filter attributes
kunit: Add module attribute
kunit: Add speed attribute
kunit: Add test attributes API structure
MAINTAINERS: add Rust KUnit files to the KUnit entry
rust: support running Rust documentation tests as KUnit ones
rust: types: make doctests compilable/testable
...
Mark the time KUnit test, time64_to_tm_test_date_range, as slow using test
attributes.
This test ran relatively much slower than most other KUnit tests.
By marking this test as slow, the test can now be filtered using the KUnit
test attribute filtering feature. Example: --filter "speed>slow". This will
run only the tests that have speeds faster than slow. The slow attribute
will also be outputted in KTAP.
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Rae Moar <rmoar@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
The nanosecond-to-millisecond skew computation uses unsigned arithmetic,
which produces user-unfriendly large positive numbers for negative skews.
Therefore, use signed arithmetic for this computation in order to preserve
the negativity.
Reported-by: Chris Bainbridge <chris.bainbridge@gmail.com>
Reported-by: Feng Tang <feng.tang@intel.com>
Fixes: dd02926994 ("clocksource: Improve "skew is too large" messages")
Reviewed-by: Feng Tang <feng.tang@intel.com>
Tested-by: Chris Bainbridge <chris.bainbridge@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Add kernel-doc for all APIs that do not already have it.
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: John Stultz <jstultz@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Acked-by: John Stultz <jstultz@google.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20230704052405.5089-3-rdunlap@infradead.org
- Fix KMSAN vs FORTIFY in strlcpy/strlcat (Alexander Potapenko)
- Convert strreplace() to return string start (Andy Shevchenko)
- Flexible array conversions (Arnd Bergmann, Wyes Karny, Kees Cook)
- Add missing function prototypes seen with W=1 (Arnd Bergmann)
- Fix strscpy() kerndoc typo (Arne Welzel)
- Replace strlcpy() with strscpy() across many subsystems which were
either Acked by respective maintainers or were trivial changes that
went ignored for multiple weeks (Azeem Shaikh)
- Remove unneeded cc-option test for UBSAN_TRAP (Nick Desaulniers)
- Add KUnit tests for strcat()-family
- Enable KUnit tests of FORTIFY wrappers under UML
- Add more complete FORTIFY protections for strlcat()
- Add missed disabling of FORTIFY for all arch purgatories.
- Enable -fstrict-flex-arrays=3 globally
- Tightening UBSAN_BOUNDS when using GCC
- Improve checkpatch to check for strcpy, strncpy, and fake flex arrays
- Improve use of const variables in FORTIFY
- Add requested struct_size_t() helper for types not pointers
- Add __counted_by macro for annotating flexible array size members
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Merge tag 'hardening-v6.5-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux
Pull hardening updates from Kees Cook:
"There are three areas of note:
A bunch of strlcpy()->strscpy() conversions ended up living in my tree
since they were either Acked by maintainers for me to carry, or got
ignored for multiple weeks (and were trivial changes).
The compiler option '-fstrict-flex-arrays=3' has been enabled
globally, and has been in -next for the entire devel cycle. This
changes compiler diagnostics (though mainly just -Warray-bounds which
is disabled) and potential UBSAN_BOUNDS and FORTIFY _warning_
coverage. In other words, there are no new restrictions, just
potentially new warnings. Any new FORTIFY warnings we've seen have
been fixed (usually in their respective subsystem trees). For more
details, see commit df8fc4e934.
The under-development compiler attribute __counted_by has been added
so that we can start annotating flexible array members with their
associated structure member that tracks the count of flexible array
elements at run-time. It is possible (likely?) that the exact syntax
of the attribute will change before it is finalized, but GCC and Clang
are working together to sort it out. Any changes can be made to the
macro while we continue to add annotations.
As an example of that last case, I have a treewide commit waiting with
such annotations found via Coccinelle:
https://git.kernel.org/linus/adc5b3cb48a049563dc673f348eab7b6beba8a9b
Also see commit dd06e72e68 for more details.
Summary:
- Fix KMSAN vs FORTIFY in strlcpy/strlcat (Alexander Potapenko)
- Convert strreplace() to return string start (Andy Shevchenko)
- Flexible array conversions (Arnd Bergmann, Wyes Karny, Kees Cook)
- Add missing function prototypes seen with W=1 (Arnd Bergmann)
- Fix strscpy() kerndoc typo (Arne Welzel)
- Replace strlcpy() with strscpy() across many subsystems which were
either Acked by respective maintainers or were trivial changes that
went ignored for multiple weeks (Azeem Shaikh)
- Remove unneeded cc-option test for UBSAN_TRAP (Nick Desaulniers)
- Add KUnit tests for strcat()-family
- Enable KUnit tests of FORTIFY wrappers under UML
- Add more complete FORTIFY protections for strlcat()
- Add missed disabling of FORTIFY for all arch purgatories.
- Enable -fstrict-flex-arrays=3 globally
- Tightening UBSAN_BOUNDS when using GCC
- Improve checkpatch to check for strcpy, strncpy, and fake flex
arrays
- Improve use of const variables in FORTIFY
- Add requested struct_size_t() helper for types not pointers
- Add __counted_by macro for annotating flexible array size members"
* tag 'hardening-v6.5-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux: (54 commits)
netfilter: ipset: Replace strlcpy with strscpy
uml: Replace strlcpy with strscpy
um: Use HOST_DIR for mrproper
kallsyms: Replace all non-returning strlcpy with strscpy
sh: Replace all non-returning strlcpy with strscpy
of/flattree: Replace all non-returning strlcpy with strscpy
sparc64: Replace all non-returning strlcpy with strscpy
Hexagon: Replace all non-returning strlcpy with strscpy
kobject: Use return value of strreplace()
lib/string_helpers: Change returned value of the strreplace()
jbd2: Avoid printing outside the boundary of the buffer
checkpatch: Check for 0-length and 1-element arrays
riscv/purgatory: Do not use fortified string functions
s390/purgatory: Do not use fortified string functions
x86/purgatory: Do not use fortified string functions
acpi: Replace struct acpi_table_slit 1-element array with flex-array
clocksource: Replace all non-returning strlcpy with strscpy
string: use __builtin_memcpy() in strlcpy/strlcat
staging: most: Replace all non-returning strlcpy with strscpy
drm/i2c: tda998x: Replace all non-returning strlcpy with strscpy
...
- Scheduler SMP load-balancer improvements:
- Avoid unnecessary migrations within SMT domains on hybrid systems.
Problem:
On hybrid CPU systems, (processors with a mixture of higher-frequency
SMT cores and lower-frequency non-SMT cores), under the old code
lower-priority CPUs pulled tasks from the higher-priority cores if
more than one SMT sibling was busy - resulting in many unnecessary
task migrations.
Solution:
The new code improves the load balancer to recognize SMT cores with more
than one busy sibling and allows lower-priority CPUs to pull tasks, which
avoids superfluous migrations and lets lower-priority cores inspect all SMT
siblings for the busiest queue.
- Implement the 'runnable boosting' feature in the EAS balancer: consider CPU
contention in frequency, EAS max util & load-balance busiest CPU selection.
This improves CPU utilization for certain workloads, while leaves other key
workloads unchanged.
- Scheduler infrastructure improvements:
- Rewrite the scheduler topology setup code by consolidating it
into the build_sched_topology() helper function and building
it dynamically on the fly.
- Resolve the local_clock() vs. noinstr complications by rewriting
the code: provide separate sched_clock_noinstr() and
local_clock_noinstr() functions to be used in instrumentation code,
and make sure it is all instrumentation-safe.
- Fixes:
- Fix a kthread_park() race with wait_woken()
- Fix misc wait_task_inactive() bugs unearthed by the -rt merge:
- Fix UP PREEMPT bug by unifying the SMP and UP implementations.
- Fix task_struct::saved_state handling.
- Fix various rq clock update bugs, unearthed by turning on the rq clock
debugging code.
- Fix the PSI WINDOW_MIN_US trigger limit, which was easy to trigger by
creating enough cgroups, by removing the warnign and restricting
window size triggers to PSI file write-permission or CAP_SYS_RESOURCE.
- Propagate SMT flags in the topology when removing degenerate domain
- Fix grub_reclaim() calculation bug in the deadline scheduler code
- Avoid resetting the min update period when it is unnecessary, in
psi_trigger_destroy().
- Don't balance a task to its current running CPU in load_balance(),
which was possible on certain NUMA topologies with overlapping
groups.
- Fix the sched-debug printing of rq->nr_uninterruptible
- Cleanups:
- Address various -Wmissing-prototype warnings, as a preparation
to (maybe) enable this warning in the future.
- Remove unused code
- Mark more functions __init
- Fix shadow-variable warnings
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'sched-core-2023-06-27' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull scheduler updates from Ingo Molnar:
"Scheduler SMP load-balancer improvements:
- Avoid unnecessary migrations within SMT domains on hybrid systems.
Problem:
On hybrid CPU systems, (processors with a mixture of
higher-frequency SMT cores and lower-frequency non-SMT cores),
under the old code lower-priority CPUs pulled tasks from the
higher-priority cores if more than one SMT sibling was busy -
resulting in many unnecessary task migrations.
Solution:
The new code improves the load balancer to recognize SMT cores
with more than one busy sibling and allows lower-priority CPUs
to pull tasks, which avoids superfluous migrations and lets
lower-priority cores inspect all SMT siblings for the busiest
queue.
- Implement the 'runnable boosting' feature in the EAS balancer:
consider CPU contention in frequency, EAS max util & load-balance
busiest CPU selection.
This improves CPU utilization for certain workloads, while leaves
other key workloads unchanged.
Scheduler infrastructure improvements:
- Rewrite the scheduler topology setup code by consolidating it into
the build_sched_topology() helper function and building it
dynamically on the fly.
- Resolve the local_clock() vs. noinstr complications by rewriting
the code: provide separate sched_clock_noinstr() and
local_clock_noinstr() functions to be used in instrumentation code,
and make sure it is all instrumentation-safe.
Fixes:
- Fix a kthread_park() race with wait_woken()
- Fix misc wait_task_inactive() bugs unearthed by the -rt merge:
- Fix UP PREEMPT bug by unifying the SMP and UP implementations
- Fix task_struct::saved_state handling
- Fix various rq clock update bugs, unearthed by turning on the rq
clock debugging code.
- Fix the PSI WINDOW_MIN_US trigger limit, which was easy to trigger
by creating enough cgroups, by removing the warnign and restricting
window size triggers to PSI file write-permission or
CAP_SYS_RESOURCE.
- Propagate SMT flags in the topology when removing degenerate domain
- Fix grub_reclaim() calculation bug in the deadline scheduler code
- Avoid resetting the min update period when it is unnecessary, in
psi_trigger_destroy().
- Don't balance a task to its current running CPU in load_balance(),
which was possible on certain NUMA topologies with overlapping
groups.
- Fix the sched-debug printing of rq->nr_uninterruptible
Cleanups:
- Address various -Wmissing-prototype warnings, as a preparation to
(maybe) enable this warning in the future.
- Remove unused code
- Mark more functions __init
- Fix shadow-variable warnings"
* tag 'sched-core-2023-06-27' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (50 commits)
sched/core: Avoid multiple calling update_rq_clock() in __cfsb_csd_unthrottle()
sched/core: Avoid double calling update_rq_clock() in __balance_push_cpu_stop()
sched/core: Fixed missing rq clock update before calling set_rq_offline()
sched/deadline: Update GRUB description in the documentation
sched/deadline: Fix bandwidth reclaim equation in GRUB
sched/wait: Fix a kthread_park race with wait_woken()
sched/topology: Mark set_sched_topology() __init
sched/fair: Rename variable cpu_util eff_util
arm64/arch_timer: Fix MMIO byteswap
sched/fair, cpufreq: Introduce 'runnable boosting'
sched/fair: Refactor CPU utilization functions
cpuidle: Use local_clock_noinstr()
sched/clock: Provide local_clock_noinstr()
x86/tsc: Provide sched_clock_noinstr()
clocksource: hyper-v: Provide noinstr sched_clock()
clocksource: hyper-v: Adjust hv_read_tsc_page_tsc() to avoid special casing U64_MAX
x86/vdso: Fix gettimeofday masking
math64: Always inline u128 version of mul_u64_u64_shr()
s390/time: Provide sched_clock_noinstr()
loongarch: Provide noinstr sched_clock_read()
...
- Core:
- A set of fixes, cleanups and enhancements to the posix timer code:
- Prevent another possible live lock scenario in the exit() path,
which affects POSIX_CPU_TIMERS_TASK_WORK enabled architectures.
- Fix a loop termination issue which was reported syzcaller/KSAN in
the posix timer ID allocation code.
That triggered a deeper look into the posix-timer code which
unearthed more small issues.
- Add missing READ/WRITE_ONCE() annotations
- Fix or remove completely outdated comments
- Document places which are subtle and completely undocumented.
- Add missing hrtimer modes to the trace event decoder
- Small cleanups and enhancements all over the place
- Drivers:
- Rework the Hyper-V clocksource and sched clock setup code
- Remove a deprecated clocksource driver
- Small fixes and enhancements all over the place
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Merge tag 'timers-core-2023-06-26' of ssh://gitolite.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull timer updates from Thomas Gleixner:
"Time, timekeeping and related device driver updates:
Core:
- A set of fixes, cleanups and enhancements to the posix timer code:
- Prevent another possible live lock scenario in the exit() path,
which affects POSIX_CPU_TIMERS_TASK_WORK enabled architectures.
- Fix a loop termination issue which was reported syzcaller/KSAN
in the posix timer ID allocation code.
That triggered a deeper look into the posix-timer code which
unearthed more small issues.
- Add missing READ/WRITE_ONCE() annotations
- Fix or remove completely outdated comments
- Document places which are subtle and completely undocumented.
- Add missing hrtimer modes to the trace event decoder
- Small cleanups and enhancements all over the place
Drivers:
- Rework the Hyper-V clocksource and sched clock setup code
- Remove a deprecated clocksource driver
- Small fixes and enhancements all over the place"
* tag 'timers-core-2023-06-26' of ssh://gitolite.kernel.org/pub/scm/linux/kernel/git/tip/tip: (39 commits)
clocksource/drivers/cadence-ttc: Fix memory leak in ttc_timer_probe
dt-bindings: timers: Add Ralink SoCs timer
clocksource/drivers/hyper-v: Rework clocksource and sched clock setup
dt-bindings: timer: brcm,kona-timer: convert to YAML
clocksource/drivers/imx-gpt: Fold <soc/imx/timer.h> into its only user
clk: imx: Drop inclusion of unused header <soc/imx/timer.h>
hrtimer: Add missing sparse annotations to hrtimer locking
clocksource/drivers/imx-gpt: Use only a single name for functions
clocksource/drivers/loongson1: Move PWM timer to clocksource framework
dt-bindings: timer: Add Loongson-1 clocksource
MIPS: Loongson32: Remove deprecated PWM timer clocksource
clocksource/drivers/ingenic-timer: Use pm_sleep_ptr() macro
tracing/timer: Add missing hrtimer modes to decode_hrtimer_mode().
posix-timers: Add sys_ni_posix_timers() prototype
tick/rcu: Fix bogus ratelimit condition
alarmtimer: Remove unnecessary (void *) cast
alarmtimer: Remove unnecessary initialization of variable 'ret'
posix-timers: Refer properly to CONFIG_HIGH_RES_TIMERS
posix-timers: Polish coding style in a few places
posix-timers: Remove pointless comments
...
Sparse warns about lock imbalance vs. the hrtimer_base lock due to missing
sparse annotations:
kernel/time/hrtimer.c:175:33: warning: context imbalance in 'lock_hrtimer_base' - wrong count at exit
kernel/time/hrtimer.c:1301:28: warning: context imbalance in 'hrtimer_start_range_ns' - unexpected unlock
kernel/time/hrtimer.c:1336:28: warning: context imbalance in 'hrtimer_try_to_cancel' - unexpected unlock
kernel/time/hrtimer.c:1457:9: warning: context imbalance in '__hrtimer_get_remaining' - unexpected unlock
Add the annotations to the relevant functions.
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230621075928.394481-1-ben.dooks@codethink.co.uk
The ratelimit logic in report_idle_softirq() is broken because the
exit condition is always true:
static int ratelimit;
if (ratelimit < 10)
return false; ---> always returns here
ratelimit++; ---> no chance to run
Make it check for >= 10 instead.
Fixes: 0345691b24 ("tick/rcu: Stop allowing RCU_SOFTIRQ in idle")
Signed-off-by: Wen Yang <wenyang.linux@foxmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/tencent_5AAA3EEAB42095C9B7740BE62FBF9A67E007@qq.com
Commit c78f261e5dcb ("posix-timers: Clarify posix_timer_fn() comments")
turns an ifdef CONFIG_HIGH_RES_TIMERS into an conditional on
"IS_ENABLED(CONFIG_HIGHRES_TIMERS)"; note that the new conditional refers
to "HIGHRES_TIMERS" not "HIGH_RES_TIMERS" as before.
Fix this typo introduced in that refactoring.
Fixes: c78f261e5dcb ("posix-timers: Clarify posix_timer_fn() comments")
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230609094643.26253-1-lukas.bulwahn@gmail.com
Make the issues vs. SIG_IGN understandable and remove the 15 years old
promise that a proper solution is already on the horizon.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/874jnrdmrq.ffs@tglx
The comment about timer lifetime at the end of the function is misplaced
and uncomprehensible.
Make it understandable and put it at the right place. Add a new comment
about the visibility of the new timer ID to user space.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20230425183313.619897296@linutronix.de
The descriptions for common_nsleep() is wrong and common_nsleep_timens()
lacks any form of comment.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20230425183313.567072835@linutronix.de
The documentation of sys_clock_settime() permissions is at a random place
and mostly word salad.
Remove it and add a concise comment into sys_clock_settime().
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20230425183313.514700292@linutronix.de
The decades old comment about Posix clock resolution is confusing at best.
Remove it and add a proper explanation to sys_clock_getres().
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20230425183313.356427330@linutronix.de
release_posix_timers() is called for cleaning up both hashed and unhashed
timers. The cases are differentiated by an argument and the usage is
hideous.
Seperate the actual free path out and use it for unhashed timers. Provide a
function for hashed timers.
No functional change.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20230425183313.301432503@linutronix.de
All usage of hash_lock is in thread context. No point in using
spin_lock_irqsave()/irqrestore() for a single usage site.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20230425183313.249063953@linutronix.de
Technically it's not required to set k_itimer::it_signal to NULL on exit()
because there is no other thread anymore which could lookup the timer
concurrently.
Set it to NULL for consistency sake and add a comment to that effect.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20230425183313.196462644@linutronix.de
k_itimer::it_signal is read lockless in the RCU protected hash lookup, but
it can be written concurrently in the timer_create() and timer_delete()
path. Annotate these places with READ_ONCE() and WRITE_ONCE()
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20230425183313.143596887@linutronix.de
Explain it better and add the CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y aspect
for completeness.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20230425183312.985681995@linutronix.de
posix_timer_add() tries to allocate a posix timer ID by starting from the
cached ID which was stored by the last successful allocation.
This is done in a loop searching the ID space for a free slot one by
one. The loop has to terminate when the search wrapped around to the
starting point.
But that's racy vs. establishing the starting point. That is read out
lockless, which leads to the following problem:
CPU0 CPU1
posix_timer_add()
start = sig->posix_timer_id;
lock(hash_lock);
... posix_timer_add()
if (++sig->posix_timer_id < 0)
start = sig->posix_timer_id;
sig->posix_timer_id = 0;
So CPU1 can observe a negative start value, i.e. -1, and the loop break
never happens because the condition can never be true:
if (sig->posix_timer_id == start)
break;
While this is unlikely to ever turn into an endless loop as the ID space is
huge (INT_MAX), the racy read of the start value caught the attention of
KCSAN and Dmitry unearthed that incorrectness.
Rewrite it so that all id operations are under the hash lock.
Reported-by: syzbot+5c54bd3eb218bb595aa9@syzkaller.appspotmail.com
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/87bkhzdn6g.ffs@tglx
itimer_delete() has a retry loop when the timer is concurrently expired. On
non-RT kernels this just spin-waits until the timer callback has completed,
except for posix CPU timers which have HAVE_POSIX_CPU_TIMERS_TASK_WORK
enabled.
In that case and on RT kernels the existing task could live lock when
preempting the task which does the timer delivery.
Replace spin_unlock() with an invocation of timer_wait_running() to handle
it the same way as the other retry loops in the posix timer code.
Fixes: ec8f954a40 ("posix-timers: Use a callback for cancel synchronization on PREEMPT_RT")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/87v8g7c50d.ffs@tglx
The tick period is aligned very early while the first clock_event_device is
registered. At that point the system runs in periodic mode and switches
later to one-shot mode if possible.
The next wake-up event is programmed based on the aligned value
(tick_next_period) but the delta value, that is used to program the
clock_event_device, is computed based on ktime_get().
With the subtracted offset, the device fires earlier than the exact time
frame. With a large enough offset the system programs the timer for the
next wake-up and the remaining time left is too small to make any boot
progress. The system hangs.
Move the alignment later to the setup of tick_sched timer. At this point
the system switches to oneshot mode and a high resolution clocksource is
available. At this point it is safe to align tick_next_period because
ktime_get() will now return accurate (not jiffies based) time.
[bigeasy: Patch description + testing].
Fixes: e9523a0d81 ("tick/common: Align tick period with the HZ tick.")
Reported-by: Mathias Krause <minipli@grsecurity.net>
Reported-by: "Bhatnagar, Rishabh" <risbhat@amazon.com>
Suggested-by: Mathias Krause <minipli@grsecurity.net>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Richard W.M. Jones <rjones@redhat.com>
Tested-by: Mathias Krause <minipli@grsecurity.net>
Acked-by: SeongJae Park <sj@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/5a56290d-806e-b9a5-f37c-f21958b5a8c0@grsecurity.net
Link: https://lore.kernel.org/12c6f9a3-d087-b824-0d05-0d18c9bc1bf3@amazon.com
Link: https://lore.kernel.org/r/20230615091830.RxMV2xf_@linutronix.de
With the intent to provide local_clock_noinstr(), a variant of
local_clock() that's safe to be called from noinstr code (with the
assumption that any such code will already be non-preemptible),
prepare for things by providing a noinstr sched_clock_noinstr() function.
Specifically, preempt_enable_*() calls out to schedule(), which upsets
noinstr validation efforts.
As such, pull out the preempt_{dis,en}able_notrace() requirements from
the sched_clock_read() implementations by explicitly providing it in
the sched_clock() function.
This further requires said sched_clock_read() functions to be noinstr
themselves, for ARCH_WANTS_NO_INSTR users. See the next few patches.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Michael Kelley <mikelley@microsoft.com> # Hyper-V
Link: https://lore.kernel.org/r/20230519102715.302350330@infradead.org
The read side of seqcount_latch consists of:
do {
seq = raw_read_seqcount_latch(&latch->seq);
...
} while (read_seqcount_latch_retry(&latch->seq, seq));
which is asymmetric in the raw_ department, and sure enough,
read_seqcount_latch_retry() includes (explicit) instrumentation where
raw_read_seqcount_latch() does not.
This inconsistency becomes a problem when trying to use it from
noinstr code. As such, fix it by renaming and re-implementing
raw_read_seqcount_latch_retry() without the instrumentation.
Specifically the instrumentation in question is kcsan_atomic_next(0)
in do___read_seqcount_retry(). Loosing this annotation is not a
problem because raw_read_seqcount_latch() does not pass through
kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX).
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Tested-by: Michael Kelley <mikelley@microsoft.com> # Hyper-V
Link: https://lore.kernel.org/r/20230519102715.233598176@infradead.org
When a tick broadcast clockevent device is initialized for one shot mode
then tick_broadcast_setup_oneshot() OR's the periodic broadcast mode
cpumask into the oneshot broadcast cpumask.
This is required when switching from periodic broadcast mode to oneshot
broadcast mode to ensure that CPUs which are waiting for periodic
broadcast are woken up on the next tick.
But it is subtly broken, when an active broadcast device is replaced and
the system is already in oneshot (NOHZ/HIGHRES) mode. Victor observed
this and debugged the issue.
Then the OR of the periodic broadcast CPU mask is wrong as the periodic
cpumask bits are sticky after tick_broadcast_enable() set it for a CPU
unless explicitly cleared via tick_broadcast_disable().
That means that this sets all other CPUs which have tick broadcasting
enabled at that point unconditionally in the oneshot broadcast mask.
If the affected CPUs were already idle and had their bits set in the
oneshot broadcast mask then this does no harm. But for non idle CPUs
which were not set this corrupts their state.
On their next invocation of tick_broadcast_enable() they observe the bit
set, which indicates that the broadcast for the CPU is already set up.
As a consequence they fail to update the broadcast event even if their
earliest expiring timer is before the actually programmed broadcast
event.
If the programmed broadcast event is far in the future, then this can
cause stalls or trigger the hung task detector.
Avoid this by telling tick_broadcast_setup_oneshot() explicitly whether
this is the initial switch over from periodic to oneshot broadcast which
must take the periodic broadcast mask into account. In the case of
initialization of a replacement device this prevents that the broadcast
oneshot mask is modified.
There is a second problem with broadcast device replacement in this
function. The broadcast device is only armed when the previous state of
the device was periodic.
That is correct for the switch from periodic broadcast mode to oneshot
broadcast mode as the underlying broadcast device could operate in
oneshot state already due to lack of periodic state in hardware. In that
case it is already armed to expire at the next tick.
For the replacement case this is wrong as the device is in shutdown
state. That means that any already pending broadcast event will not be
armed.
This went unnoticed because any CPU which goes idle will observe that
the broadcast device has an expiry time of KTIME_MAX and therefore any
CPUs next timer event will be earlier and cause a reprogramming of the
broadcast device. But that does not guarantee that the events of the
CPUs which were already in idle are delivered on time.
Fix this by arming the newly installed device for an immediate event
which will reevaluate the per CPU expiry times and reprogram the
broadcast device accordingly. This is simpler than caching the last
expiry time in yet another place or saving it before the device exchange
and handing it down to the setup function. Replacement of broadcast
devices is not a frequent operation and usually happens once somewhere
late in the boot process.
Fixes: 9c336c9935 ("tick/broadcast: Allow late registered device to enter oneshot mode")
Reported-by: Victor Hassan <victor@allwinnertech.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/87pm7d2z1i.ffs@tglx
- A trivial documentation fix in the timekeeping core
- A really boring set of small fixes, enhancements and cleanups in the
drivers code. No new clocksource/clockevent drivers for a change.
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Merge tag 'timers-core-2023-04-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull more timer updates from Thomas Gleixner:
"Timekeeping and clocksource/event driver updates the second batch:
- A trivial documentation fix in the timekeeping core
- A really boring set of small fixes, enhancements and cleanups in
the drivers code. No new clocksource/clockevent drivers for a
change"
* tag 'timers-core-2023-04-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
timekeeping: Fix references to nonexistent ktime_get_fast_ns()
dt-bindings: timer: rockchip: Add rk3588 compatible
dt-bindings: timer: rockchip: Drop superfluous rk3288 compatible
clocksource/drivers/ti: Use of_property_read_bool() for boolean properties
clocksource/drivers/timer-ti-dm: Fix finding alwon timer
clocksource/drivers/davinci: Fix memory leak in davinci_timer_register when init fails
clocksource/drivers/stm32-lp: Drop of_match_ptr for ID table
clocksource/drivers/timer-ti-dm: Convert to platform remove callback returning void
clocksource/drivers/timer-tegra186: Convert to platform remove callback returning void
clocksource/drivers/timer-ti-dm: Improve error message in .remove
clocksource/drivers/timer-stm32-lp: Mark driver as non-removable
clocksource/drivers/sh_mtu2: Mark driver as non-removable
clocksource/drivers/timer-ti-dm: Use of_address_to_resource()
clocksource/drivers/timer-imx-gpt: Remove non-DT function
clocksource/drivers/timer-mediatek: Split out CPUXGPT timers
clocksource/drivers/exynos_mct: Explicitly return 0 for shared timer
Here is the large set of driver core changes for 6.4-rc1.
Once again, a busy development cycle, with lots of changes happening in
the driver core in the quest to be able to move "struct bus" and "struct
class" into read-only memory, a task now complete with these changes.
This will make the future rust interactions with the driver core more
"provably correct" as well as providing more obvious lifetime rules for
all busses and classes in the kernel.
The changes required for this did touch many individual classes and
busses as many callbacks were changed to take const * parameters
instead. All of these changes have been submitted to the various
subsystem maintainers, giving them plenty of time to review, and most of
them actually did so.
Other than those changes, included in here are a small set of other
things:
- kobject logging improvements
- cacheinfo improvements and updates
- obligatory fw_devlink updates and fixes
- documentation updates
- device property cleanups and const * changes
- firwmare loader dependency fixes.
All of these have been in linux-next for a while with no reported
problems.
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Merge tag 'driver-core-6.4-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core
Pull driver core updates from Greg KH:
"Here is the large set of driver core changes for 6.4-rc1.
Once again, a busy development cycle, with lots of changes happening
in the driver core in the quest to be able to move "struct bus" and
"struct class" into read-only memory, a task now complete with these
changes.
This will make the future rust interactions with the driver core more
"provably correct" as well as providing more obvious lifetime rules
for all busses and classes in the kernel.
The changes required for this did touch many individual classes and
busses as many callbacks were changed to take const * parameters
instead. All of these changes have been submitted to the various
subsystem maintainers, giving them plenty of time to review, and most
of them actually did so.
Other than those changes, included in here are a small set of other
things:
- kobject logging improvements
- cacheinfo improvements and updates
- obligatory fw_devlink updates and fixes
- documentation updates
- device property cleanups and const * changes
- firwmare loader dependency fixes.
All of these have been in linux-next for a while with no reported
problems"
* tag 'driver-core-6.4-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core: (120 commits)
device property: make device_property functions take const device *
driver core: update comments in device_rename()
driver core: Don't require dynamic_debug for initcall_debug probe timing
firmware_loader: rework crypto dependencies
firmware_loader: Strip off \n from customized path
zram: fix up permission for the hot_add sysfs file
cacheinfo: Add use_arch[|_cache]_info field/function
arch_topology: Remove early cacheinfo error message if -ENOENT
cacheinfo: Check cache properties are present in DT
cacheinfo: Check sib_leaf in cache_leaves_are_shared()
cacheinfo: Allow early level detection when DT/ACPI info is missing/broken
cacheinfo: Add arm64 early level initializer implementation
cacheinfo: Add arch specific early level initializer
tty: make tty_class a static const structure
driver core: class: remove struct class_interface * from callbacks
driver core: class: mark the struct class in struct class_interface constant
driver core: class: make class_register() take a const *
driver core: class: mark class_release() as taking a const *
driver core: remove incorrect comment for device_create*
MIPS: vpe-cmp: remove module owner pointer from struct class usage.
...
There was never a function named ktime_get_fast_ns().
Presumably these should refer to ktime_get_mono_fast_ns() instead.
Fixes: c1ce406e80 ("timekeeping: Fix up function documentation for the NMI safe accessors")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John Stultz <jstultz@google.com>
Link: https://lore.kernel.org/r/06df7b3cbd94f016403bbf6cd2b38e4368e7468f.1682516546.git.geert+renesas@glider.be
- Improve the VDSO build time checks to cover all dynamic relocations
VDSO does not allow dynamic relcations, but the build time check is
incomplete and fragile.
It's based on architectures specifying the relocation types to search
for and does not handle R_*_NONE relocation entries correctly.
R_*_NONE relocations are injected by some GNU ld variants if they fail
to determine the exact .rel[a]/dyn_size to cover trailing zeros.
R_*_NONE relocations must be ignored by dynamic loaders, so they
should be ignored in the build time check too.
Remove the architecture specific relocation types to check for and
validate strictly that no other relocations than R_*_NONE end up
in the VSDO .so file.
- Prefer signal delivery to the current thread for
CLOCK_PROCESS_CPUTIME_ID based posix-timers
Such timers prefer to deliver the signal to the main thread of a
process even if the context in which the timer expires is the current
task. This has the downside that it might wake up an idle thread.
As there is no requirement or guarantee that the signal has to be
delivered to the main thread, avoid this by preferring the current
task if it is part of the thread group which shares sighand.
This not only avoids waking idle threads, it also distributes the
signal delivery in case of multiple timers firing in the context
of different threads close to each other better.
- Align the tick period properly (again)
For a long time the tick was starting at CLOCK_MONOTONIC zero, which
allowed users space applications to either align with the tick or to
place a periodic computation so that it does not interfere with the
tick. The alignement of the tick period was more by chance than by
intention as the tick is set up before a high resolution clocksource is
installed, i.e. timekeeping is still tick based and the tick period
advances from there.
The early enablement of sched_clock() broke this alignement as the time
accumulated by sched_clock() is taken into account when timekeeping is
initialized. So the base value now(CLOCK_MONOTONIC) is not longer a
multiple of tick periods, which breaks applications which relied on
that behaviour.
Cure this by aligning the tick starting point to the next multiple of
tick periods, i.e 1000ms/CONFIG_HZ.
- A set of NOHZ fixes and enhancements
- Cure the concurrent writer race for idle and IO sleeptime statistics
The statitic values which are exposed via /proc/stat are updated from
the CPU local idle exit and remotely by cpufreq, but that happens
without any form of serialization. As a consequence sleeptimes can be
accounted twice or worse.
Prevent this by restricting the accumulation writeback to the CPU
local idle exit and let the remote access compute the accumulated
value.
- Protect idle/iowait sleep time with a sequence count
Reading idle/iowait sleep time, e.g. from /proc/stat, can race with
idle exit updates. As a consequence the readout may result in random
and potentially going backwards values.
Protect this by a sequence count, which fixes the idle time
statistics issue, but cannot fix the iowait time problem because
iowait time accounting races with remote wake ups decrementing the
remote runqueues nr_iowait counter. The latter is impossible to fix,
so the only way to deal with that is to document it properly and to
remove the assertion in the selftest which triggers occasionally due
to that.
- Restructure struct tick_sched for better cache layout
- Some small cleanups and a better cache layout for struct tick_sched
- Implement the missing timer_wait_running() callback for POSIX CPU timers
For unknown reason the introduction of the timer_wait_running() callback
missed to fixup posix CPU timers, which went unnoticed for almost four
years.
While initially only targeted to prevent livelocks between a timer
deletion and the timer expiry function on PREEMPT_RT enabled kernels, it
turned out that fixing this for mainline is not as trivial as just
implementing a stub similar to the hrtimer/timer callbacks.
The reason is that for CONFIG_POSIX_CPU_TIMERS_TASK_WORK enabled systems
there is a livelock issue independent of RT.
CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y moves the expiry of POSIX CPU timers
out from hard interrupt context to task work, which is handled before
returning to user space or to a VM. The expiry mechanism moves the
expired timers to a stack local list head with sighand lock held. Once
sighand is dropped the task can be preempted and a task which wants to
delete a timer will spin-wait until the expiry task is scheduled back
in. In the worst case this will end up in a livelock when the preempting
task and the expiry task are pinned on the same CPU.
The timer wheel has a timer_wait_running() mechanism for RT, which uses
a per CPU timer-base expiry lock which is held by the expiry code and the
task waiting for the timer function to complete blocks on that lock.
This does not work in the same way for posix CPU timers as there is no
timer base and expiry for process wide timers can run on any task
belonging to that process, but the concept of waiting on an expiry lock
can be used too in a slightly different way.
Add a per task mutex to struct posix_cputimers_work, let the expiry task
hold it accross the expiry function and let the deleting task which
waits for the expiry to complete block on the mutex.
In the non-contended case this results in an extra mutex_lock()/unlock()
pair on both sides.
This avoids spin-waiting on a task which is scheduled out, prevents the
livelock and cures the problem for RT and !RT systems.
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Merge tag 'timers-core-2023-04-24' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull timers and timekeeping updates from Thomas Gleixner:
- Improve the VDSO build time checks to cover all dynamic relocations
VDSO does not allow dynamic relocations, but the build time check is
incomplete and fragile.
It's based on architectures specifying the relocation types to search
for and does not handle R_*_NONE relocation entries correctly.
R_*_NONE relocations are injected by some GNU ld variants if they
fail to determine the exact .rel[a]/dyn_size to cover trailing zeros.
R_*_NONE relocations must be ignored by dynamic loaders, so they
should be ignored in the build time check too.
Remove the architecture specific relocation types to check for and
validate strictly that no other relocations than R_*_NONE end up in
the VSDO .so file.
- Prefer signal delivery to the current thread for
CLOCK_PROCESS_CPUTIME_ID based posix-timers
Such timers prefer to deliver the signal to the main thread of a
process even if the context in which the timer expires is the current
task. This has the downside that it might wake up an idle thread.
As there is no requirement or guarantee that the signal has to be
delivered to the main thread, avoid this by preferring the current
task if it is part of the thread group which shares sighand.
This not only avoids waking idle threads, it also distributes the
signal delivery in case of multiple timers firing in the context of
different threads close to each other better.
- Align the tick period properly (again)
For a long time the tick was starting at CLOCK_MONOTONIC zero, which
allowed users space applications to either align with the tick or to
place a periodic computation so that it does not interfere with the
tick. The alignement of the tick period was more by chance than by
intention as the tick is set up before a high resolution clocksource
is installed, i.e. timekeeping is still tick based and the tick
period advances from there.
The early enablement of sched_clock() broke this alignement as the
time accumulated by sched_clock() is taken into account when
timekeeping is initialized. So the base value now(CLOCK_MONOTONIC) is
not longer a multiple of tick periods, which breaks applications
which relied on that behaviour.
Cure this by aligning the tick starting point to the next multiple of
tick periods, i.e 1000ms/CONFIG_HZ.
- A set of NOHZ fixes and enhancements:
* Cure the concurrent writer race for idle and IO sleeptime
statistics
The statitic values which are exposed via /proc/stat are updated
from the CPU local idle exit and remotely by cpufreq, but that
happens without any form of serialization. As a consequence
sleeptimes can be accounted twice or worse.
Prevent this by restricting the accumulation writeback to the CPU
local idle exit and let the remote access compute the accumulated
value.
* Protect idle/iowait sleep time with a sequence count
Reading idle/iowait sleep time, e.g. from /proc/stat, can race
with idle exit updates. As a consequence the readout may result
in random and potentially going backwards values.
Protect this by a sequence count, which fixes the idle time
statistics issue, but cannot fix the iowait time problem because
iowait time accounting races with remote wake ups decrementing
the remote runqueues nr_iowait counter. The latter is impossible
to fix, so the only way to deal with that is to document it
properly and to remove the assertion in the selftest which
triggers occasionally due to that.
* Restructure struct tick_sched for better cache layout
* Some small cleanups and a better cache layout for struct
tick_sched
- Implement the missing timer_wait_running() callback for POSIX CPU
timers
For unknown reason the introduction of the timer_wait_running()
callback missed to fixup posix CPU timers, which went unnoticed for
almost four years.
While initially only targeted to prevent livelocks between a timer
deletion and the timer expiry function on PREEMPT_RT enabled kernels,
it turned out that fixing this for mainline is not as trivial as just
implementing a stub similar to the hrtimer/timer callbacks.
The reason is that for CONFIG_POSIX_CPU_TIMERS_TASK_WORK enabled
systems there is a livelock issue independent of RT.
CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y moves the expiry of POSIX CPU
timers out from hard interrupt context to task work, which is handled
before returning to user space or to a VM. The expiry mechanism moves
the expired timers to a stack local list head with sighand lock held.
Once sighand is dropped the task can be preempted and a task which
wants to delete a timer will spin-wait until the expiry task is
scheduled back in. In the worst case this will end up in a livelock
when the preempting task and the expiry task are pinned on the same
CPU.
The timer wheel has a timer_wait_running() mechanism for RT, which
uses a per CPU timer-base expiry lock which is held by the expiry
code and the task waiting for the timer function to complete blocks
on that lock.
This does not work in the same way for posix CPU timers as there is
no timer base and expiry for process wide timers can run on any task
belonging to that process, but the concept of waiting on an expiry
lock can be used too in a slightly different way.
Add a per task mutex to struct posix_cputimers_work, let the expiry
task hold it accross the expiry function and let the deleting task
which waits for the expiry to complete block on the mutex.
In the non-contended case this results in an extra
mutex_lock()/unlock() pair on both sides.
This avoids spin-waiting on a task which is scheduled out, prevents
the livelock and cures the problem for RT and !RT systems
* tag 'timers-core-2023-04-24' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
posix-cpu-timers: Implement the missing timer_wait_running callback
selftests/proc: Assert clock_gettime(CLOCK_BOOTTIME) VS /proc/uptime monotonicity
selftests/proc: Remove idle time monotonicity assertions
MAINTAINERS: Remove stale email address
timers/nohz: Remove middle-function __tick_nohz_idle_stop_tick()
timers/nohz: Add a comment about broken iowait counter update race
timers/nohz: Protect idle/iowait sleep time under seqcount
timers/nohz: Only ever update sleeptime from idle exit
timers/nohz: Restructure and reshuffle struct tick_sched
tick/common: Align tick period with the HZ tick.
selftests/timers/posix_timers: Test delivery of signals across threads
posix-timers: Prefer delivery of signals to the current thread
vdso: Improve cmd_vdso_check to check all dynamic relocations
For some unknown reason the introduction of the timer_wait_running callback
missed to fixup posix CPU timers, which went unnoticed for almost four years.
Marco reported recently that the WARN_ON() in timer_wait_running()
triggers with a posix CPU timer test case.
Posix CPU timers have two execution models for expiring timers depending on
CONFIG_POSIX_CPU_TIMERS_TASK_WORK:
1) If not enabled, the expiry happens in hard interrupt context so
spin waiting on the remote CPU is reasonably time bound.
Implement an empty stub function for that case.
2) If enabled, the expiry happens in task work before returning to user
space or guest mode. The expired timers are marked as firing and moved
from the timer queue to a local list head with sighand lock held. Once
the timers are moved, sighand lock is dropped and the expiry happens in
fully preemptible context. That means the expiring task can be scheduled
out, migrated, interrupted etc. So spin waiting on it is more than
suboptimal.
The timer wheel has a timer_wait_running() mechanism for RT, which uses
a per CPU timer-base expiry lock which is held by the expiry code and the
task waiting for the timer function to complete blocks on that lock.
This does not work in the same way for posix CPU timers as there is no
timer base and expiry for process wide timers can run on any task
belonging to that process, but the concept of waiting on an expiry lock
can be used too in a slightly different way:
- Add a mutex to struct posix_cputimers_work. This struct is per task
and used to schedule the expiry task work from the timer interrupt.
- Add a task_struct pointer to struct cpu_timer which is used to store
a the task which runs the expiry. That's filled in when the task
moves the expired timers to the local expiry list. That's not
affecting the size of the k_itimer union as there are bigger union
members already
- Let the task take the expiry mutex around the expiry function
- Let the waiter acquire a task reference with rcu_read_lock() held and
block on the expiry mutex
This avoids spin-waiting on a task which might not even be on a CPU and
works nicely for RT too.
Fixes: ec8f954a40 ("posix-timers: Use a callback for cancel synchronization on PREEMPT_RT")
Reported-by: Marco Elver <elver@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Marco Elver <elver@google.com>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/87zg764ojw.ffs@tglx
There is no need for the __tick_nohz_idle_stop_tick() function between
tick_nohz_idle_stop_tick() and its implementation. Remove that
unnecessary step.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230222144649.624380-6-frederic@kernel.org
The per-cpu iowait task counter is incremented locally upon sleeping.
But since the task can be woken to (and by) another CPU, the counter may
then be decremented remotely. This is the source of a race involving
readers VS writer of idle/iowait sleeptime.
The following scenario shows an example where a /proc/stat reader
observes a pending sleep time as IO whereas that pending sleep time
later eventually gets accounted as non-IO.
CPU 0 CPU 1 CPU 2
----- ----- ------
//io_schedule() TASK A
current->in_iowait = 1
rq(0)->nr_iowait++
//switch to idle
// READ /proc/stat
// See nr_iowait_cpu(0) == 1
return ts->iowait_sleeptime +
ktime_sub(ktime_get(), ts->idle_entrytime)
//try_to_wake_up(TASK A)
rq(0)->nr_iowait--
//idle exit
// See nr_iowait_cpu(0) == 0
ts->idle_sleeptime += ktime_sub(ktime_get(), ts->idle_entrytime)
As a result subsequent reads on /proc/stat may expose backward progress.
This is unfortunately hardly fixable. Just add a comment about that
condition.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230222144649.624380-5-frederic@kernel.org
Reading idle/IO sleep time (eg: from /proc/stat) can race with idle exit
updates because the state machine handling the stats is not atomic and
requires a coherent read batch.
As a result reading the sleep time may report irrelevant or backward
values.
Fix this with protecting the simple state machine within a seqcount.
This is expected to be cheap enough not to add measurable performance
impact on the idle path.
Note this only fixes reader VS writer condition partitially. A race
remains that involves remote updates of the CPU iowait task counter. It
can hardly be fixed.
Reported-by: Yu Liao <liaoyu15@huawei.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230222144649.624380-4-frederic@kernel.org
The idle and IO sleeptime statistics appearing in /proc/stat can be
currently updated from two sites: locally on idle exit and remotely
by cpufreq. However there is no synchronization mechanism protecting
concurrent updates. It is therefore possible to account the sleeptime
twice, among all the other possible broken scenarios.
To prevent from breaking the sleeptime accounting source, restrict the
sleeptime updates to the local idle exit site. If there is a delta to
add since the last update, IO/Idle sleep time readers will now only
compute the delta without actually writing it back to the internal idle
statistic fields.
This fixes a writer VS writer race. Note there are still two known
reader VS writer races to handle. A subsequent patch will fix one.
Reported-by: Yu Liao <liaoyu15@huawei.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230222144649.624380-3-frederic@kernel.org
Restructure and group fields by access in order to optimize cache
layout. While at it, also add missing kernel doc for two fields:
@last_jiffies and @idle_expires.
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230222144649.624380-2-frederic@kernel.org
Linus Torvalds