linux-kernel - [PATCH 1/2] posix-cpu-timers: avoid do_sys_times() races with __exit

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Message-ID: <20090612103403.2e1d576f@dhcp-lab-109.englab.brq.redhat.com>
Date:	Fri, 12 Jun 2009 10:34:03 +0200
From:	Stanislaw Gruszka <sgruszka@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH 1/2] posix-cpu-timers: avoid do_sys_times() races with
 __exit_signal()

Protect thread_group_cputime() call by siglock, to avoid possible (but
to be honest - very improbable) double times accounting of exiting task.
This is revert of commit 2b5fe6de58276d0b5a7c884d5dbfc300ca47db78
"thread_group_cputime: move a couple of callsites outside of ->siglock",
but implementation of thread_group_cputime() was different then.

In thread_group_cputime() we loop on all threads within the group to sum 
they cputimes. After finish loop, we add killed tasks times from tsk->signal.
If thread (one or more) exit in gap between loop and adding killed tasks
times, __exit_signal() function add already accounted times to tsk->signal.

Signed-off-by: Stanislaw Gruszka <sgruszka@...hat.com>
---
 kernel/sys.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/sys.c b/kernel/sys.c
index e7998cf..0805d08 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -913,8 +913,8 @@ void do_sys_times(struct tms *tms)
 	struct task_cputime cputime;
 	cputime_t cutime, cstime;

-	thread_group_cputime(current, &cputime);
 	spin_lock_irq(&current->sighand->siglock);
+	thread_group_cputime(current, &cputime);
 	cutime = current->signal->cutime;
 	cstime = current->signal->cstime;
 	spin_unlock_irq(&current->sighand->siglock);
-- 
1.6.0.6

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