linux-kernel - [PATCH] __exit_signal: don't take rcu lock

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Message-ID: <20080531161527.GA5560@tv-sign.ru>
Date:	Sat, 31 May 2008 20:15:27 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] __exit_signal: don't take rcu lock

There is no reason for rcu_read_lock() in __exit_signal(). tsk->sighand can
only be changed if tsk does exec, obviously this is not possible.

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

--- 26-rc2/kernel/exit.c~0_ES_NO_RCU	2008-05-26 18:09:12.000000000 +0400
+++ 26-rc2/kernel/exit.c	2008-05-31 20:08:11.000000000 +0400
@@ -84,7 +84,6 @@ static void __exit_signal(struct task_st
 	BUG_ON(!sig);
 	BUG_ON(!atomic_read(&sig->count));
 
-	rcu_read_lock();
 	sighand = rcu_dereference(tsk->sighand);
 	spin_lock(&sighand->siglock);
 
@@ -135,7 +134,6 @@ static void __exit_signal(struct task_st
 	tsk->signal = NULL;
 	tsk->sighand = NULL;
 	spin_unlock(&sighand->siglock);
-	rcu_read_unlock();
 
 	__cleanup_sighand(sighand);
 	clear_tsk_thread_flag(tsk,TIF_SIGPENDING);

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