linux-kernel - [PATCH] do_task_stat: don't take rcu_read

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Date:	Wed, 20 Feb 2008 20:09:13 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Pavel Emelyanov <xemul@...ru>, linux-kernel@...r.kernel.org
Subject: [PATCH] do_task_stat: don't take rcu_read_lock()

(depends on "[PATCH 1/2] lock_task_sighand: add rcu lock/unlock",
 http://marc.info/?l=linux-kernel&m=120335433821564)

lock_task_sighand() was changed, and do_task_stat() doesn't need rcu_read_lock
any longer. sighand->siglock protects all "interesting" fields.

Except: it doesn't protect ->tty->pgrp, but neither does rcu_read_lock(), this
should be fixed.

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

--- MM/fs/proc/array.c~DTS	2008-02-17 23:40:07.000000000 +0300
+++ MM/fs/proc/array.c	2008-02-20 19:53:37.000000000 +0300
@@ -425,7 +425,6 @@ static int do_task_stat(struct seq_file 
 	cutime = cstime = utime = stime = cputime_zero;
 	cgtime = gtime = cputime_zero;
 
-	rcu_read_lock();
 	if (lock_task_sighand(task, &flags)) {
 		struct signal_struct *sig = task->signal;
 
@@ -469,7 +468,6 @@ static int do_task_stat(struct seq_file 
 
 		unlock_task_sighand(task, &flags);
 	}
-	rcu_read_unlock();
 
 	if (!whole || num_threads < 2)
 		wchan = get_wchan(task);

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