Re: [Linux-kernel-mentees] [PATCH] sched.h: Annotate sighand_struct with __rcu

["Paul E. McKenney" <paulmck@kernel.org>]

On Sat, Jan 25, 2020 at 10:41:06PM +0100, Christian Brauner wrote:
> On January 24, 2020 5:59:08 AM GMT+01:00, madhuparnabhowmik10@gmail.com wrote:
> >From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
> >
> >This patch fixes the following sparse errors by annotating the
> >sighand_struct with __rcu
> >
> >kernel/fork.c:1511:9: error: incompatible types in comparison
> >expression
> >kernel/exit.c:100:19: error: incompatible types in comparison
> >expression
> >kernel/signal.c:1370:27: error: incompatible types in comparison
> >expression
> >
> >This fix introduces the following sparse error in signal.c due to
> >checking the sighand pointer without rcu primitives:
> >
> >kernel/signal.c:1386:21: error: incompatible types in comparison
> >expression
> >
> >This new sparse error is also fixed in this patch.
> >
> >Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>

Acked-by: Paul E. McKenney <paulmck@kernel.org>

> >---
> > include/linux/sched.h | 2 +-
> > kernel/signal.c       | 2 +-
> > 2 files changed, 2 insertions(+), 2 deletions(-)
> >
> >diff --git a/include/linux/sched.h b/include/linux/sched.h
> >index b511e178a89f..7a351360ad54 100644
> >--- a/include/linux/sched.h
> >+++ b/include/linux/sched.h
> >@@ -918,7 +918,7 @@ struct task_struct {
> > 
> > 	/* Signal handlers: */
> > 	struct signal_struct		*signal;
> >-	struct sighand_struct		*sighand;
> >+	struct sighand_struct __rcu		*sighand;
> > 	sigset_t			blocked;
> > 	sigset_t			real_blocked;
> > 	/* Restored if set_restore_sigmask() was used: */
> >diff --git a/kernel/signal.c b/kernel/signal.c
> >index bcd46f547db3..9ad8dea93dbb 100644
> >--- a/kernel/signal.c
> >+++ b/kernel/signal.c
> >@@ -1383,7 +1383,7 @@ struct sighand_struct *__lock_task_sighand(struct
> >task_struct *tsk,
> > 		 * must see ->sighand == NULL.
> > 		 */
> > 		spin_lock_irqsave(&sighand->siglock, *flags);
> >-		if (likely(sighand == tsk->sighand))
> >+		if (likely(sighand == rcu_access_pointer(tsk->sighand)))
> > 			break;
> > 		spin_unlock_irqrestore(&sighand->siglock, *flags);
> > 	}
> 
> If Paul is happy with this and nobody wants to take it I'll pick this up.

Works for me!

							Thanx, Paul
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