Commit 30f1e3dd authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

[PATCH] run_posix_cpu_timers: remove a bogus BUG_ON()

do_exit() clears ->it_##clock##_expires, but nothing prevents
another cpu to attach the timer to exiting process after that.
arm_timer() tries to protect against this race, but the check
is racy.

After exit_notify() does 'write_unlock_irq(&tasklist_lock)' and
before do_exit() calls 'schedule() local timer interrupt can find
tsk->exit_state != 0. If that state was EXIT_DEAD (or another cpu
does sys_wait4) interrupted task has ->signal == NULL.

At this moment exiting task has no pending cpu timers, they were
cleanuped in __exit_signal()->posix_cpu_timers_exit{,_group}(),
so we can just return from irq.

John Stultz recently confirmed this bug, see

Signed-off-by: default avatarOleg Nesterov <>
Signed-off-by: default avatarLinus Torvalds <>
parent 8f17fc20
......@@ -881,14 +881,6 @@ fastcall NORET_TYPE void do_exit(long code)
tsk->flags |= PF_EXITING;
* Make sure we don't try to process any timer firings
* while we are already exiting.
tsk->it_virt_expires = cputime_zero;
tsk->it_prof_expires = cputime_zero;
tsk->it_sched_expires = 0;
if (unlikely(in_atomic()))
printk(KERN_INFO "note: %s[%d] exited with preempt_count %d\n",
current->comm, current->pid,
......@@ -1288,12 +1288,11 @@ void run_posix_cpu_timers(struct task_struct *tsk)
* Double-check with locks held.
if (likely(tsk->signal != NULL)) {
......@@ -1312,6 +1311,7 @@ void run_posix_cpu_timers(struct task_struct *tsk)
* spin until we've taken care of that timer below.
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