[PATCH] cputime: avoid do_sys_times() races with __exit_signal()

[Stanislaw Gruszka]

When process exit in the middle of thread_group_cputime() loop, {u,s}time
values will be accounted twice. One time - in all threads loop, second - in
__exit_signal(). This make sys_times() return values bigger then they
are in real. Next consecutive call to sys_times() can return correct values,
so we have {u,s}time decrease.

To fix use sighand->siglock in do_sys_times().

This is partial fix for problem of utime/stime values decreasing described
in this thread:

http://lkml.org/lkml/2009/11/3/522

To fully fix the problem, we need second fix for mishmash between
task_{u,s}time() and tsk->{u,s}time. It's not clear now how this mishmash
should be fixed.

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

diff --git a/kernel/sys.c b/kernel/sys.c
index ce17760..8be5b75 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -914,8 +914,8 @@ 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);
-- 
1.6.2.5

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