diff options
| author | Oleg Nesterov <oleg@redhat.com> | 2025-06-13 19:26:50 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2025-06-19 15:32:34 +0200 |
| commit | c29d5318708e67ac13c1b6fc1007d179fb65b4d7 (patch) | |
| tree | 68bbc4005a1ce780c2de7fa955be9ac8ede7f9c9 | |
| parent | 74388368927e9c52a69524af5bbd6c55eb4690de (diff) | |
posix-cpu-timers: fix race between handle_posix_cpu_timers() and posix_cpu_timer_del()
commit f90fff1e152dedf52b932240ebbd670d83330eca upstream.
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: 0bdd2ed4138e ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | kernel/time/posix-cpu-timers.c | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c index 6bcee4704059..d44641108ba8 100644 --- a/kernel/time/posix-cpu-timers.c +++ b/kernel/time/posix-cpu-timers.c @@ -1401,6 +1401,15 @@ 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. */ |