archive/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2025-08-15 14:11:42 +02:00
Code Issues Projects Releases Packages Wiki Activity Actions

posix-cpu-timers: fix race between handle_posix_cpu_timers() and posix_cpu_timer_del()

Browse source 
If an exiting non-autoreaping task has already passed exit_notify() and
calls handle_posix_cpu_timers() from IRQ, it can be reaped by its parent
or debugger right after unlock_task_sighand().

If a concurrent posix_cpu_timer_del() runs at that moment, it won't be
able to detect timer->it.cpu.firing != 0: cpu_timer_task_rcu() and/or
lock_task_sighand() will fail.

Add the tsk->exit_state check into run_posix_cpu_timers() to fix this.

This fix is not needed if CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y, because
exit_task_work() is called before exit_notify(). But the check still
makes sense, task_work_add(&tsk->posix_cputimers_work.work) will fail
anyway in this case.

Cc: stable@vger.kernel.org
Reported-by: Benoît Sevens <bsevens@google.com>
Fixes: 0bdd2ed413 ("sched: run_posix_cpu_timers: Don't check ->exit_state, use lock_task_sighand()")
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2025-06-13 19:26:50 +02:00 • committed by Linus Torvalds
parent 3ca933aad0
commit f90fff1e15
1 changed files with 9 additions and 0 deletions
Download patch file Download diff file Expand all files Collapse all files

9
kernel/time/posix-cpu-timers.c
View file

@ -1405,6 +1405,15 @@ void run_posix_cpu_timers(void)
lockdep_assert_irqs_disabled();
/*
* Ensure that release_task(tsk) can't happen while
* handle_posix_cpu_timers() is running. Otherwise, a concurrent
* posix_cpu_timer_del() may fail to lock_task_sighand(tsk) and
* miss timer->it.cpu.firing != 0.
*/
if (tsk->exit_state)
return;
/*
* If the actual expiry is deferred to task work context and the
* work is already scheduled there is no point to do anything here.