linux-kernel - [PATCH 4/3] thread_group_cputime: move a couple of callsites outside of ->siglock

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Message-ID: <20081117144008.GA5386@redhat.com>
Date:	Mon, 17 Nov 2008 15:40:08 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Roland McGrath <roland@...hat.com>
Cc:	Doug Chapman <doug.chapman@...com>,
	Frank Mayhar <fmayhar@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 4/3] thread_group_cputime: move a couple of callsites
	outside of ->siglock

->siglock buys nothing for thread_group_cputime() in do_sys_times() and
wait_task_zombie() (which btw takes the unrelated parent's ->siglock).
Actually I think do_sys_times() doesn't need ->siglock at all.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>

--- K-28/kernel/exit.c~SYS_TIMES_NO_SIGLOCK	2008-11-10 15:07:22.000000000 +0100
+++ K-28/kernel/exit.c	2008-11-17 02:02:12.000000000 +0100
@@ -1330,10 +1330,10 @@ static int wait_task_zombie(struct task_
 		 * group, which consolidates times for all threads in the
 		 * group including the group leader.
 		 */
+		thread_group_cputime(p, &cputime);
 		spin_lock_irq(&p->parent->sighand->siglock);
 		psig = p->parent->signal;
 		sig = p->signal;
-		thread_group_cputime(p, &cputime);
 		psig->cutime =
 			cputime_add(psig->cutime,
 			cputime_add(cputime.utime,
--- K-28/kernel/sys.c~SYS_TIMES_NO_SIGLOCK	2008-11-06 19:11:02.000000000 +0100
+++ K-28/kernel/sys.c	2008-11-17 01:56:17.000000000 +0100
@@ -858,8 +858,8 @@ void do_sys_times(struct tms *tms)
 	struct task_cputime cputime;
 	cputime_t cutime, cstime;
 
-	spin_lock_irq(&current->sighand->siglock);
 	thread_group_cputime(current, &cputime);
+	spin_lock_irq(&current->sighand->siglock);
 	cutime = current->signal->cutime;
 	cstime = current->signal->cstime;
 	spin_unlock_irq(&current->sighand->siglock);

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