linux-kernel - Re: [PATCH] sched.h: Annotate sighand_struct with _

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Date:   Sat, 25 Jan 2020 22:41:06 +0100
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     madhuparnabhowmik10@...il.com, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, ebiederm@...ssion.com, oleg@...hat.com,
        paulmck@...nel.org
CC:     joel@...lfernandes.org, linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        frextrite@...il.com, rcu@...r.kernel.org,
        Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
Subject: Re: [PATCH] sched.h: Annotate sighand_struct with __rcu

On January 24, 2020 5:59:08 AM GMT+01:00, madhuparnabhowmik10@...il.com wrote:
>From: Madhuparna Bhowmik <madhuparnabhowmik10@...il.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@...il.com>
>---
> 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.

Thanks!
Christian