This commit adds a rcupdate.rcu_task_enqueue_lim module parameter that
sets the initial number of callback queues to use for the RCU Tasks
family of RCU implementations. This parameter allows testing of various
fanout values.
Reported-by: Martin Lau <kafai@fb.com>
Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Currently, rcu_barrier_tasks(), rcu_barrier_tasks_rude(),
and rcu_barrier_tasks_trace() simply invoke the corresponding
synchronize_rcu_tasks*() function. This works because there is only
one callback queue.
However, there will soon be multiple callback queues. This commit
therefore scans the queues currently in use, entraining a callback on
each non-empty queue. Sequence numbers and reference counts are used
to synchronize this process in a manner similar to the approach taken
by rcu_barrier().
Reported-by: Martin Lau <kafai@fb.com>
Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
If there is a flood of callbacks, it is necessary to put multiple
CPUs to work invoking those callbacks. This commit therefore uses a
workqueue-flooding approach to parallelize RCU Tasks callback execution.
Reported-by: Martin Lau <kafai@fb.com>
Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds a rcu_tasks_invoke_cbs() function that invokes all
ready callbacks on all of the per-CPU lists that are currently in use.
Reported-by: Martin Lau <kafai@fb.com>
Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds a rcu_tasks_need_gpcb() function that returns an
indication of whether another grace period is required, and if no grace
period is required, whether there are callbacks that need to be invoked.
The function scans all per-CPU lists currently in use.
Reported-by: Martin Lau <kafai@fb.com>
Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds a ->percpu_enqueue_lim field to the rcu_tasks structure.
This field contains two to the power of the ->percpu_enqueue_shift
field, easing construction of iterators over the per-CPU queues that
might contain RCU Tasks callbacks. Such iterators will be introduced
in later commits.
Reported-by: Martin Lau <kafai@fb.com>
Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit renames the rcu_tasks_percpu structure's ->cbs_pcpu_lock
to ->lock and then uses spin_lock_rcu_node() and friends to acquire and
release this lock, preparing for upcoming commits that will spread the
grace-period process across multiple CPUs and kthreads.
[ paulmck: Apply feedback from kernel test robot. ]
Reported-by: Martin Lau <kafai@fb.com>
Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit moves from a bespoke head and tail pointer in the
rcu_tasks_percpu structure to an rcu_segcblist structure, thus allowing
associating the grace-period sequence number with groups of callbacks.
This in turn will allow callbacks to be invoked independently on
different CPUs.
Reported-by: Martin Lau <kafai@fb.com>
Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit moves the rcu_tasks structure's ->n_gps grace-period-counter
field to a ->task_gp_seq grce-period sequence number in order to enable
use of the rcu_segcblist structure for the callback lists. This in turn
permits CPUs to lag behind the RCU Tasks grace-period sequence number
without suffering long-term slowdowns in callback invocation.
Reported-by: Martin Lau <kafai@fb.com>
Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit introduces a ->percpu_enqueue_shift field to the rcu_tasks
structure, and uses it to shift down the CPU number in order to
select a rcu_tasks_percpu structure. This field is currently set to a
sufficiently large shift count to always select the CPU-0 instance of
the rcu_tasks_percpu structure, and later commits will adjust this.
Reported-by: Martin Lau <kafai@fb.com>
Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Currently, RCU Tasks Trace (as well as the other two flavors of RCU Tasks)
use a single global callback list. This works well and is simple, but
expected changes in workload will cause this list to become a bottleneck.
This commit therefore creates per-CPU callback lists for the various
flavors of RCU Tasks, but continues queueing on a single list, namely
that of CPU 0. Later commits will dynamically vary the number of lists
in use to accommodate dynamic changes in workload.
Reported-by: Martin Lau <kafai@fb.com>
Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Tested-by: kernel test robot <beibei.si@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Currently, the check_all_holdout_tasks_trace() function removes all tasks
marked with ->trc_reader_checked from the holdout list, including those
with IPIs pending. This means that the IPI handler might arrive at
a task that has already been removed from the list, which is at best
an accident waiting to happen.
This commit therefore avoids removing tasks with IPIs pending from
the holdout list. This in turn means that the "if" condition in the
for_each_online_cpu() loop in rcu_tasks_trace_postgp() should always
evaluate to false, so a WARN_ON_ONCE() is added to check that.
Signed-off-by: Paul E. McKenney <paulmck@kernel.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
...
Give try_invoke_on_locked_down_task() a saner name and have it return
an int so that the caller might distinguish between different reasons
of failure.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Tested-by: Vasily Gorbik <gor@linux.ibm.com> # on s390
Link: https://lkml.kernel.org/r/20210929152428.649944917@infradead.org
The cond_resched_rcu_qs() function no longer exists, despite being mentioned
several times in kernel/rcu/tasks.h. This commit therefore updates it to
the current cond_resched_tasks_rcu_qs().
Reported-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The trc_wait_for_one_reader() function is called at multiple stages
of trace rcu-tasks GP function, rcu_tasks_wait_gp():
- First, it is called as part of per task function -
rcu_tasks_trace_pertask(), for all non-idle tasks. As part of per task
processing, this function add the task in the holdout list and if the
task is currently running on a CPU, it sends IPI to the task's CPU.
The IPI handler takes action depending on whether task is in trace
rcu-tasks read side critical section or not:
- a. If the task is in trace rcu-tasks read side critical section
(t->trc_reader_nesting != 0), the IPI handler sets the task's
->trc_reader_special.b.need_qs, so that this task notifies exit
from its outermost read side critical section (by decrementing
trc_n_readers_need_end) to the GP handling function.
trc_wait_for_one_reader() also increments trc_n_readers_need_end,
so that the trace rcu-tasks GP handler function waits for this
task's read side exit notification. The IPI handler also sets
t->trc_reader_checked to true, and no further IPIs are sent for
this task, for this trace rcu-tasks grace period and this
task can be removed from holdout list.
- b. If the task is in the process of exiting its trace rcu-tasks
read side critical section, (t->trc_reader_nesting < 0), defer
this task's processing to future calls to trc_wait_for_one_reader().
- c. If task is not in rcu-task read side critical section,
t->trc_reader_nesting == 0, ->trc_reader_checked is set for this
task, so that this task is removed from holdout list.
- Second, trc_wait_for_one_reader() is called as part of post scan, in
function rcu_tasks_trace_postscan(), for all idle tasks.
- Third, in function check_all_holdout_tasks_trace(), this function is
called for each task in the holdout list, but only if there isn't
a pending IPI for the task (->trc_ipi_to_cpu == -1). This function
removed the task from holdout list, if IPI handler has completed the
required work, to ensure that the current trace rcu-tasks grace period
either waits for this task, or this task is not in a trace rcu-tasks
read side critical section.
Now, considering the scenario where smp_call_function_single() fails in
first case, inside rcu_tasks_trace_pertask(). In this case,
->trc_ipi_to_cpu is set to the current CPU for that task. This will
result in trc_wait_for_one_reader() getting skipped in third case,
inside check_all_holdout_tasks_trace(), for this task. This further
results in ->trc_reader_checked never getting set for this task,
and the task not getting removed from holdout list. This can cause
the current trace rcu-tasks grace period to stall.
Fix the above problem, by resetting ->trc_ipi_to_cpu to -1, on
smp_call_function_single() failure, so that future IPI calls can
be send for this task.
Note that all three of the trc_wait_for_one_reader() function's
callers (rcu_tasks_trace_pertask(), rcu_tasks_trace_postscan(),
check_all_holdout_tasks_trace()) hold cpu_read_lock(). This means
that smp_call_function_single() cannot race with CPU hotplug, and thus
should never fail. Therefore, also add a warning in order to report
any such failure in case smp_call_function_single() grows some other
reason for failure.
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
call_rcu_tasks_trace() does have read-side primitives - rcu_read_lock_trace()
and rcu_read_unlock_trace(). Fix this information in the comments.
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
RCU tasks rude variant does not check whether the current
running context on a CPU is usermode. Read side critical section ends
on transition to usermode execution, by the virtue of usermode
execution being schedulable. Clarify this in comments for
call_rcu_tasks_rude() and synchronize_rcu_tasks_rude().
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Valid CPU numbers can be zero or greater, but the checks for
->trc_ipi_to_cpu and tick_nohz_full_cpu()'s argument are for strictly
greater than. This commit therefore corrects the check for no_hz_full
cpu in show_stalled_task_trace() so as to include cpu 0.
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
In check_all_holdout_tasks_trace(), firstreport is a pointer argument;
so, check the dereferenced value, instead of checking the pointer.
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Early in debugging, it made some sense to differentiate the first
iteration from subsequent iterations, but now this just causes confusion.
This commit therefore moves the "set_tasks_gp_state(rtp, RTGS_WAIT_CBS)"
statement to the beginning of the "for" loop in rcu_tasks_kthread().
Reported-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The second argument of rcu_read_unlock_trace_special() is always zero.
When called from exit_tasks_rcu_finish_trace(), it is the constant
zero, and rcu_read_unlock_trace_special() doesn't get called from
rcu_read_unlock_trace() unless the value of local variable "nesting"
is zero because in that case the early return is taken instead.
This commit therefore removes the "nesting" argument from the
rcu_read_unlock_trace_special() function, substituting the constant
zero within that function. This commit also adds a WARN_ON_ONCE()
to rcu_read_lock_trace_held() in case non-zeroness some day appears.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Currently, trc_inspect_reader() treats a task exiting its RCU Tasks
Trace read-side critical section the same as being within that critical
section. However, this can fail because that task might have already
checked its .need_qs field, which means that it might never decrement
the all-important trc_n_readers_need_end counter. Of course, for that
to happen, the task would need to never again execute an RCU Tasks Trace
read-side critical section, but this really could happen if the system's
last trampoline was removed. Note that exit from such a critical section
cannot be treated as a quiescent state due to the possibility of nested
critical sections. This means that if trc_inspect_reader() sees a
negative nesting value, it must set up to try again later.
This commit therefore ignores tasks that are exiting their RCU Tasks
Trace read-side critical sections so that they will be rechecked later.
[ paulmck: Apply feedback from Neeraj Upadhyay and Boqun Feng. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Currently, trc_wait_for_one_reader() atomically increments
the trc_n_readers_need_end counter before sending the IPI
invoking trc_read_check_handler(). All failure paths out of
trc_read_check_handler() and also from the smp_call_function_single()
within trc_wait_for_one_reader() must carefully atomically decrement
this counter. This is more complex than it needs to be.
This commit therefore simplifies things and saves a few lines of
code by dispensing with the atomic decrements in favor of having
trc_read_check_handler() do the atomic increment only in the success case.
In theory, this represents no change in functionality.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Currently, RCU Tasks Trace initializes the trc_n_readers_need_end counter
to the value one, increments it before each trc_read_check_handler()
IPI, then decrements it within trc_read_check_handler() if the target
task was in a quiescent state (or if the target task moved to some other
CPU while the IPI was in flight), complaining if the new value was zero.
The rationale for complaining is that the initial value of one must be
decremented away before zero can be reached, and this decrement has not
yet happened.
Except that trc_read_check_handler() is initiated with an asynchronous
smp_call_function_single(), which might be significantly delayed. This
can result in false-positive complaints about the counter reaching zero.
This commit therefore waits for in-flight IPI handlers to complete before
decrementing away the initial value of one from the trc_n_readers_need_end
counter.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
There are a few remaining locations in kernel/rcu that still use
"&per_cpu()". This commit replaces them with "per_cpu_ptr(&)", and does
not introduce any functional change.
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Liu Song <liu.song11@zte.com.cn>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit replaces the fictitious synchronize_rcu_rude() function with
its real-world synchronize_rcu_tasks_rude() counterpart.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
There are several ->trc_reader_special.b.need_qs data races that are
too low-probability for KCSAN to notice, but which will happen sooner
or later. This commit therefore marks these accesses.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
There are several ->trc_reader_nesting data races that are too
low-probability for KCSAN to notice, but which will happen sooner or
later. This commit therefore marks these accesses, and comments one
that cannot race.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Accesses to task_struct structures must be either protected by RCU
or by get_task_struct(). Tasks trace RCU uses these in a non-obvious
combination, in conjunction with an IPI handler. This commit therefore
adds comments explaining this usage.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Invoking trc_del_holdout() from within trc_wait_for_one_reader() is
only a performance optimization because the RCU Tasks Trace grace-period
kthread will eventually do this within check_all_holdout_tasks_trace().
But it is not a particularly important performance optimization because
it only applies to the grace-period kthread, of which there is but one.
This commit therefore removes this invocation of trc_del_holdout() in
favor of the one in check_all_holdout_tasks_trace() in the grace-period
kthread.
Reported-by: "Xu, Yanfei" <yanfei.xu@windriver.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
As Yanfei pointed out, although invoking trc_del_holdout() is safe
from the viewpoint of the integrity of the holdout list itself,
the put_task_struct() invoked by trc_del_holdout() can result in
use-after-free errors due to later accesses to this task_struct structure
by the RCU Tasks Trace grace-period kthread.
This commit therefore removes this call to trc_del_holdout() from
trc_inspect_reader() in favor of the grace-period thread's existing call
to trc_del_holdout(), thus eliminating that particular class of
use-after-free errors.
Reported-by: "Xu, Yanfei" <yanfei.xu@windriver.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
In some architectures, the no-op variant of show_rcu_tasks_gp_kthreads()
get "no previous prototype" compiler warnings. These are false positives
given that kernel/rcu/tasks.h is included only once. But why put up
with the compiler noise?
This commit therefore adds "static inline" to this definition to force
the compiler to accept this situation, while also moving it to its proper
place in kernel/rcu/rcu.h.
Reported-by: kernel test robot <lkp@intel.com>
[ paulmck: Update per Stephen Rothwell feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Fix ~12 single-word typos in RCU code comments.
[ paulmck: Apply feedback from Randy Dunlap. ]
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds a block comment that gives a high-level overview of
how RCU Rude grace periods progress. It also gives an overview of the
memory ordering.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds a block comment that gives a high-level overview of how
RCU tasks grace periods progress. It also adds a note about how exiting
tasks are handled, plus it gives an overview of the memory ordering.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds a block comment that gives a high-level overview of
how RCU tasks trace grace periods progress. It also adds a note about
how exiting tasks are handled, plus it gives an overview of the memory
ordering.
Reported-by: Peter Zijlstra <peterz@infradead.org>
Reported-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
[ paulmck: Fix commit log per Mathieu Desnoyers feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The command 'find ./kernel/rcu/ | xargs ./scripts/kernel-doc -none'
reported an issue with the kernel-doc of struct rcu_tasks.
This commit rectifies the kernel-doc, such that no issues remain for
./kernel/rcu/.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds self tests for early-boot use of RCU-tasks grace periods.
It tests all three variants (Rude, Tasks, and Tasks Trace) and covers
both synchronous (e.g., synchronize_rcu_tasks()) and asynchronous (e.g.,
call_rcu_tasks()) grace-period APIs.
Self-tests are run only in kernels built with CONFIG_PROVE_RCU=y.
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
[ paulmck: Handle CONFIG_PROVE_RCU=n and identify test cases' callbacks. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
PowerPC testing encountered boot failures due to RCU Tasks not being
fully initialized until core_initcall() time. This commit therefore
initializes RCU Tasks (along with Rude RCU and RCU Tasks Trace) just
before early_initcall() time, thus allowing waiting on RCU Tasks grace
periods from early_initcall() handlers.
Link: https://lore.kernel.org/rcu/87eekfh80a.fsf@dja-thinkpad.axtens.net/
Fixes: 36dadef23f ("kprobes: Init kprobes in early_initcall")
Tested-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Currently, the units of ->init_fract are milliseconds while those of
->gp_sleep are jiffies. For consistency with each other and with the
argument of schedule_timeout_idle(), this commit changes the units of
->init_fract to jiffies.
This change does affect the backoff algorithm, but only on systems where
HZ is not 1000, and even there the change makes more sense, given that the
current setup would "back off" to the same number of jiffies repeatedly.
In contrast, with this change, the number of jiffies waited increases
on each pass through the loop in the rcu_tasks_wait_gp() function.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
At the end of the test and after rcu_torture_writer() stalls, rcutorture
invokes show_rcu_gp_kthreads() in order to dump out information on the
RCU grace-period kthread. This makes a lot of sense when testing vanilla
RCU, but not so much for the other flavors. This commit therefore allows
per-flavor kthread-dump functions to be specified.
[ paulmck: Apply feedback from kernel test robot <lkp@intel.com>. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The infinite for-loop in rcu_tasks_wait_gp() has its only exit at the
top of the loop, so this commit does the straightforward conversion to
a while-loop, thus saving a few lines.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The rcu_tasks_trace_postgp() function uses for_each_process_thread()
to scan the task list without the benefit of RCU read-side protection,
which can result in use-after-free errors on task_struct structures.
This error was missed because the TRACE01 rcutorture scenario enables
lockdep, but also builds with CONFIG_PREEMPT_NONE=y. In this situation,
preemption is disabled everywhere, so lockdep thinks everywhere can
be a legitimate RCU reader. This commit therefore adds the needed
rcu_read_lock() and rcu_read_unlock().
Note that this bug can occur only after an RCU Tasks Trace CPU stall
warning, which by default only happens after a grace period has extended
for ten minutes (yes, not a typo, minutes).
Fixes: 4593e772b5 ("rcu-tasks: Add stall warnings for RCU Tasks Trace")
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: <bpf@vger.kernel.org>
Cc: <stable@vger.kernel.org> # 5.7.x
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Paul E. McKenney