linux-kernel - [PATCH 1/2] lock_task_sighand: add rcu lock/unlock

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Date:	Mon, 18 Feb 2008 20:07:32 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] lock_task_sighand: add rcu lock/unlock

Most of the callers of lock_task_sighand() doesn't actually need rcu_lock().
lock_task_sighand() needs it only to safely play with tsk->sighand, it can take
the lock itself.

Signed-off-by: Oleg Nesterov <oleg@...sign.ru>

--- 25/kernel/signal.c~1_LTS_RCU	2008-02-15 20:34:32.000000000 +0300
+++ 25/kernel/signal.c	2008-02-18 18:35:04.000000000 +0300
@@ -978,13 +978,11 @@ int fastcall __fatal_signal_pending(stru
 }
 EXPORT_SYMBOL(__fatal_signal_pending);
 
-/*
- * Must be called under rcu_read_lock() or with tasklist_lock read-held.
- */
 struct sighand_struct *lock_task_sighand(struct task_struct *tsk, unsigned long *flags)
 {
 	struct sighand_struct *sighand;
 
+	rcu_read_lock();
 	for (;;) {
 		sighand = rcu_dereference(tsk->sighand);
 		if (unlikely(sighand == NULL))
@@ -995,6 +993,7 @@ struct sighand_struct *lock_task_sighand
 			break;
 		spin_unlock_irqrestore(&sighand->siglock, *flags);
 	}
+	rcu_read_unlock();
 
 	return sighand;
 }

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