On 05/05, Oleg Nesterov wrote:
>
> On 05/05, Paul E. McKenney wrote:
> >
> > Does the patch below cover it?
>
> Yes, thanks.
>
> Acked-by: Oleg Nesterov <o...@redhat.com>
Yes, but please consider the cleanup below, on top of your change.
This is subjective of course, but imho the code looks better without
the extra unlock/restore inside the loop.
-------------------------------------------------------------------------------
Subject: [PATCH] signal: Simplify __lock_task_sighand()
__lock_task_sighand() does local_irq_save() to prevent the potential
deadlock, we can use preempt_disable() with the same effect. And in
this case we can do preempt_disable/enable + rcu_read_lock/unlock only
once outside of the main loop and simplify the code. Also shaves 112
bytes from signal.o.
Signed-off-by: Oleg Nesterov <o...@redhat.com>
---
kernel/signal.c | 31 +++++++++++++------------------
1 files changed, 13 insertions(+), 18 deletions(-)
diff --git a/kernel/signal.c b/kernel/signal.c
index 4368370..03a0fd4 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1260,30 +1260,25 @@ struct sighand_struct *__lock_task_sighand(struct
task_struct *tsk,
unsigned long *flags)
{
struct sighand_struct *sighand;
-
+ /*
+ * We are going to do rcu_read_unlock() under spin_lock_irqsave().
+ * Make sure we can not be preempted after rcu_read_unlock(), see
+ * rcu_read_unlock comment header for details.
+ */
+ preempt_disable();
+ rcu_read_lock();
for (;;) {
- /*
- * Disable interrupts early to avoid deadlocks.
- * See rcu_read_unlock comment header for details.
- */
- local_irq_save(*flags);
- rcu_read_lock();
sighand = rcu_dereference(tsk->sighand);
- if (unlikely(sighand == NULL)) {
- rcu_read_unlock();
- local_irq_restore(*flags);
+ if (unlikely(sighand == NULL))
break;
- }
- spin_lock(&sighand->siglock);
- if (likely(sighand == tsk->sighand)) {
- rcu_read_unlock();
+ spin_lock_irqsave(&sighand->siglock, *flags);
+ if (likely(sighand == tsk->sighand))
break;
- }
- spin_unlock(&sighand->siglock);
- rcu_read_unlock();
- local_irq_restore(*flags);
+ spin_unlock_irqrestore(&sighand->siglock, *flags);
}
+ rcu_read_unlock();
+ preempt_enable();
return sighand;
}
--
1.5.5.1
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