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Commit 0bdd2ed4 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Ingo Molnar
Browse files

sched: run_posix_cpu_timers: Don't check ->exit_state, use lock_task_sighand() 



run_posix_cpu_timers() doesn't work if current has already passed
exit_notify(). This was needed to prevent the races with do_wait().

Since ea6d290c ->signal is always valid and can't go away. We can
remove the "tsk->exit_state == 0" in fastpath_timer_check() and
convert run_posix_cpu_timers() to use lock_task_sighand().

Note: it makes sense to take group_leader's sighand instead, the
sub-thread still uses CPU after release_task(). But we need more
changes to do this.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100610231018.GA25942@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent bfac7009

kernel/posix-cpu-timers.c

+4 −6
Original line number Diff line number Diff line
@@ -1272,10 +1272,6 @@ static inline int fastpath_timer_check(struct task_struct *tsk) 
{

	struct signal_struct *sig;



	/* tsk == current, ensure it is safe to use ->signal/sighand */

	if (unlikely(tsk->exit_state))

		return 0;



	if (!task_cputime_zero(&tsk->cputime_expires)) {

		struct task_cputime task_sample = {

			.utime = tsk->utime,
@@ -1308,6 +1304,7 @@ void run_posix_cpu_timers(struct task_struct *tsk) 
{

	LIST_HEAD(firing);

	struct k_itimer *timer, *next;

	unsigned long flags;



	BUG_ON(!irqs_disabled());
@@ -1318,7 +1315,8 @@ void run_posix_cpu_timers(struct task_struct *tsk) 
	if (!fastpath_timer_check(tsk))

		return;



	spin_lock(&tsk->sighand->siglock);

	if (!lock_task_sighand(tsk, &flags))

		return;

	/*

	 * Here we take off tsk->signal->cpu_timers[N] and

	 * tsk->cpu_timers[N] all the timers that are firing, and
@@ -1340,7 +1338,7 @@ void run_posix_cpu_timers(struct task_struct *tsk) 
	 * that gets the timer lock before we do will give it up and

	 * spin until we've taken care of that timer below.

	 */

	spin_unlock(&tsk->sighand->siglock);

	unlock_task_sighand(tsk, &flags);



	/*

	 * Now that all the timers on our list have the firing flag,