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From:   madhuparnabhowmik10@gmail.com
To:     mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, ebiederm@xmission.com,
        christian.brauner@ubuntu.com, oleg@redhat.com, paulmck@kernel.org
Cc:     joel@joelfernandes.org, linux-kernel@vger.kernel.org,
        linux-kernel-mentees@lists.linuxfoundation.org,
        frextrite@gmail.com, rcu@vger.kernel.org,
        Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
Subject: [PATCH] sched.h: Annotate sighand_struct with __rcu
Date:   Thu, 23 Jan 2020 20:23:05 +0530
Message-Id: <20200123145305.10652-1-madhuparnabhowmik10@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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 addressed in this patch.

Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
---
 include/linux/sched.h | 2 +-
 kernel/signal.c       | 3 ++-
 2 files changed, 3 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..1272def37462 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1383,7 +1383,8 @@ 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_dereference_protected(tsk->sighand,
+						lockdep_is_held(&sighand->siglock))))
 			break;
 		spin_unlock_irqrestore(&sighand->siglock, *flags);
 	}
-- 
2.17.1