linux-kernel - [PATCH 2/3] futex_find_get_task: don't take tasklist

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Message-ID: <20060821170621.GA1643@oleg>
Date:	Mon, 21 Aug 2006 21:06:21 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Andrew Morton <akpm@...l.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/3] futex_find_get_task: don't take tasklist_lock

It is ok to do find_task_by_pid() + get_task_struct() under rcu_read_lock(),
we cand drop tasklist_lock.

Note that testing of ->exit_state is racy with or without tasklist anyway.

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

--- 2.6.18-rc4/kernel/futex.c~2_ffgt	2006-08-21 20:32:48.000000000 +0400
+++ 2.6.18-rc4/kernel/futex.c	2006-08-21 20:41:15.000000000 +0400
@@ -389,7 +389,7 @@ static struct task_struct * futex_find_g
 {
 	struct task_struct *p;
 
-	read_lock(&tasklist_lock);
+	rcu_read_lock();
 	p = find_task_by_pid(pid);
 	if (!p)
 		goto out_unlock;
@@ -403,7 +403,7 @@ static struct task_struct * futex_find_g
 	}
 	get_task_struct(p);
 out_unlock:
-	read_unlock(&tasklist_lock);
+	rcu_read_unlock();
 
 	return p;
 }

-
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