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cpu-timers: Avoid iterating over all threads in fastpath_timer_check()

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Spread p->sighand->siglock locking scope to make sure that
fastpath_timer_check() never iterates over all threads. Without
locking there is small possibility that signal->cputimer will stop
running while we write values to signal->cputime_expires.

Calling thread_group_cputime() from fastpath_timer_check() is not only
bad because it is slow, also it is racy with __exit_signal() which can
lead to invalid signal->{s,u}time values.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Stanislaw Gruszka 2010-03-11 14:04:42 -08:00 committed by Thomas Gleixner
parent 1f169f84d2
commit c28739375b
1 changed files with 7 additions and 7 deletions
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14
kernel/posix-cpu-timers.c
View file

@ -550,7 +550,7 @@ static inline int expires_gt(cputime_t expires, cputime_t new_exp)
/*
* Insert the timer on the appropriate list before any timers that
* expire later. This must be called with the tasklist_lock held
* for reading, and interrupts disabled.
* for reading, interrupts disabled and p->sighand->siglock taken.
*/
static void arm_timer(struct k_itimer *timer)
{
@ -569,9 +569,6 @@ static void arm_timer(struct k_itimer *timer)
}
head += CPUCLOCK_WHICH(timer->it_clock);
BUG_ON(!irqs_disabled());
spin_lock(&p->sighand->siglock);
listpos = head;
list_for_each_entry(next, head, entry) {
if (cpu_time_before(timer->it_clock, nt->expires, next->expires))
@ -606,8 +603,6 @@ static void arm_timer(struct k_itimer *timer)
break;
}
}
spin_unlock(&p->sighand->siglock);
}
/*
@ -720,7 +715,6 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags,
ret = TIMER_RETRY;
} else
list_del_init(&timer->it.cpu.entry);
spin_unlock(&p->sighand->siglock);
/*
* We need to sample the current value to convert the new
@ -774,6 +768,7 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags,
* disable this firing since we are already reporting
* it as an overrun (thanks to bump_cpu_timer above).
*/
spin_unlock(&p->sighand->siglock);
read_unlock(&tasklist_lock);
goto out;
}
@ -793,6 +788,7 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags,
arm_timer(timer);
}
spin_unlock(&p->sighand->siglock);
read_unlock(&tasklist_lock);
/*
@ -1206,6 +1202,7 @@ void posix_cpu_timer_schedule(struct k_itimer *timer)
goto out;
}
read_lock(&tasklist_lock); /* arm_timer needs it. */
spin_lock(&p->sighand->siglock);
} else {
read_lock(&tasklist_lock);
if (unlikely(p->signal == NULL)) {
@ -1226,6 +1223,7 @@ void posix_cpu_timer_schedule(struct k_itimer *timer)
clear_dead_task(timer, now);
goto out_unlock;
}
spin_lock(&p->sighand->siglock);
cpu_timer_sample_group(timer->it_clock, p, &now);
bump_cpu_timer(timer, now);
/* Leave the tasklist_lock locked for the call below. */
@ -1234,7 +1232,9 @@ void posix_cpu_timer_schedule(struct k_itimer *timer)
/*
* Now re-arm for the new expiry time.
*/
BUG_ON(!irqs_disabled());
arm_timer(timer);
spin_unlock(&p->sighand->siglock);
out_unlock:
read_unlock(&tasklist_lock);