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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: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100610231018.GA25942@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Oleg Nesterov 2010-06-11 01:10:18 +02:00 committed by Ingo Molnar
parent bfac700918
commit 0bdd2ed413
1 changed files with 4 additions and 6 deletions
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10
kernel/posix-cpu-timers.c
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@ -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,