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sched: Fix ttwu() for __ARCH_WANT_INTERRUPTS_ON_CTXSW

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Marc reported that e4a52bcb9 (sched: Remove rq->lock from the first
half of ttwu()) broke his ARM-SMP machine. Now ARM is one of the few
__ARCH_WANT_INTERRUPTS_ON_CTXSW users, so that exception in the ttwu()
code was suspect.

Yong found that the interrupt could hit after context_switch() changes
current but before it clears p->on_cpu, if that interrupt were to
attempt a wake-up of p we would indeed find ourselves spinning in IRQ
context.

Fix this by reverting to the old behaviour for this situation and
perform a full remote wake-up.

Cc: Frank Rowand <frank.rowand@am.sony.com>
Cc: Yong Zhang <yong.zhang0@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Reported-by: Marc Zyngier <Marc.Zyngier@arm.com>
Tested-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2011-05-26 14:21:33 +02:00 committed by Ingo Molnar
parent cd4ae6adf8
commit d6aa8f85f1
1 changed files with 28 additions and 9 deletions
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37
kernel/sched.c
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@ -2573,7 +2573,26 @@ static void ttwu_queue_remote(struct task_struct *p, int cpu)
if (!next)
smp_send_reschedule(cpu);
}
#endif
#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
static int ttwu_activate_remote(struct task_struct *p, int wake_flags)
{
struct rq *rq;
int ret = 0;
rq = __task_rq_lock(p);
if (p->on_cpu) {
ttwu_activate(rq, p, ENQUEUE_WAKEUP);
ttwu_do_wakeup(rq, p, wake_flags);
ret = 1;
}
__task_rq_unlock(rq);
return ret;
}
#endif /* __ARCH_WANT_INTERRUPTS_ON_CTXSW */
#endif /* CONFIG_SMP */
static void ttwu_queue(struct task_struct *p, int cpu)
{
@ -2631,17 +2650,17 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
while (p->on_cpu) {
#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
/*
* If called from interrupt context we could have landed in the
* middle of schedule(), in this case we should take care not
* to spin on ->on_cpu if p is current, since that would
* deadlock.
* In case the architecture enables interrupts in
* context_switch(), we cannot busy wait, since that
* would lead to deadlocks when an interrupt hits and
* tries to wake up @prev. So bail and do a complete
* remote wakeup.
*/
if (p == current) {
ttwu_queue(p, cpu);
if (ttwu_activate_remote(p, wake_flags))
goto stat;
}
#endif
#else
cpu_relax();
#endif
}
/*
* Pairs with the smp_wmb() in finish_lock_switch().