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[PATCH] posix-timers: remove false BUG_ON() from run_posix_cpu_timers()
do_exit() clears ->it_##clock##_expires, but nothing prevents another cpu to attach the timer to exiting process after that. 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 cleaned up in __exit_signal()->posix_cpu_timers_exit{,_group}(), so we can just return from irq. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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@ -825,14 +825,6 @@ fastcall NORET_TYPE void do_exit(long code)
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tsk->flags |= PF_EXITING;
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/*
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* Make sure we don't try to process any timer firings
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* while we are already exiting.
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*/
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tsk->it_virt_expires = cputime_zero;
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tsk->it_prof_expires = cputime_zero;
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tsk->it_sched_expires = 0;
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if (unlikely(in_atomic()))
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printk(KERN_INFO "note: %s[%d] exited with preempt_count %d\n",
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current->comm, current->pid,
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@ -1285,30 +1285,30 @@ void run_posix_cpu_timers(struct task_struct *tsk)
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#undef UNEXPIRED
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BUG_ON(tsk->exit_state);
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/*
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* Double-check with locks held.
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*/
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read_lock(&tasklist_lock);
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spin_lock(&tsk->sighand->siglock);
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if (likely(tsk->signal != NULL)) {
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spin_lock(&tsk->sighand->siglock);
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/*
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* Here we take off tsk->cpu_timers[N] and tsk->signal->cpu_timers[N]
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* all the timers that are firing, and put them on the firing list.
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*/
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check_thread_timers(tsk, &firing);
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check_process_timers(tsk, &firing);
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/*
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* Here we take off tsk->cpu_timers[N] and tsk->signal->cpu_timers[N]
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* all the timers that are firing, and put them on the firing list.
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*/
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check_thread_timers(tsk, &firing);
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check_process_timers(tsk, &firing);
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/*
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* We must release these locks before taking any timer's lock.
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* There is a potential race with timer deletion here, as the
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* siglock now protects our private firing list. We have set
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* the firing flag in each timer, so that a deletion attempt
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* that gets the timer lock before we do will give it up and
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* spin until we've taken care of that timer below.
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*/
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spin_unlock(&tsk->sighand->siglock);
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/*
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* We must release these locks before taking any timer's lock.
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* There is a potential race with timer deletion here, as the
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* siglock now protects our private firing list. We have set
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* the firing flag in each timer, so that a deletion attempt
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* that gets the timer lock before we do will give it up and
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* spin until we've taken care of that timer below.
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*/
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spin_unlock(&tsk->sighand->siglock);
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}
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read_unlock(&tasklist_lock);
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/*
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