On Tue, Jul 08, 2014 at 05:01:51PM +0800, Lai Jiangshan wrote:
> On 07/08/2014 06:38 AM, Paul E. McKenney wrote:
> > From: "Paul E. McKenney" <paul...@linux.vnet.ibm.com>
> >
> > The explicit local_irq_save() in __lock_task_sighand() is needed to avoid
> > a potential deadlock condition, as noted in a841796f11c90d53 (signal:
> > align __lock_task_sighand() irq disabling and RCU). However, someone
> > reading the code might be forgiven for concluding that this separate
> > local_irq_save() was completely unnecessary. This commit therefore adds
> > a comment referencing the shiny new block comment on rcu_read_unlock().
> >
> > Reported-by: Oleg Nesterov <o...@redhat.com>
> > Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> > Acked-by: Oleg Nesterov <o...@redhat.com>
> > ---
> > kernel/signal.c | 4 ++++
> > 1 file changed, 4 insertions(+)
> >
> > diff --git a/kernel/signal.c b/kernel/signal.c
> > index a4077e90f19f..46161e744760 100644
> > --- a/kernel/signal.c
> > +++ b/kernel/signal.c
> > @@ -1263,6 +1263,10 @@ struct sighand_struct *__lock_task_sighand(struct
> > task_struct *tsk,
> > struct sighand_struct *sighand;
> >
> > for (;;) {
> > + /*
> > + * Disable interrupts early to avoid deadlocks.
> > + * See rcu_read_unlock comment header for details.
> > + */
>
> A pair of brackets are missing here: rcu_read_unlock()
> after that, please add:
>
> Reviewed-by: Lai Jiangshan <la...@cn.fujitsu.com>
Good point, added the "()" and your Reviewed-by.
> It reminds me that I should keep my effort to solve the deadlock
> problem where rcu_read_unlock() is overlapped with schedule locks.
That would be good! I vaguely remember an earlier patch of yours that
Steven Rostedt gave feedback on, but have not been able to locate either
email.
Thanx, Paul
> > local_irq_save(*flags);
> > rcu_read_lock();
> > sighand = rcu_dereference(tsk->sighand);
>
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