posix-timers: correctly get dying task time sample in posix_cpu_timer_schedule()
authorFrederic Weisbecker <fweisbec@gmail.com>
Fri, 28 Jun 2013 00:06:43 +0000 (00:06 +0000)
committerFrederic Weisbecker <fweisbec@gmail.com>
Wed, 3 Jul 2013 14:20:20 +0000 (16:20 +0200)
commit76cdcdd979ce00f5037804d73da583fb488ec1b2
treec0959aaea64748a44f99e1e9ffef6b8eee179c53
parent0bc4b0cf15708fca04095232c4e448634e94d029
posix-timers: correctly get dying task time sample in posix_cpu_timer_schedule()

In order to re-arm a timer after it fired, we take a sample of the current
process or thread cputime.

If the task is dying though, we don't arm anything but we cache the
remaining timer expiration delta for further reads.

Something similar is performed in posix_cpu_timer_get() but here we forget
to take the process wide cputime sample before caching it.

As a result we are storing random stack content, leading every further
reads of that timer to return junk values.

Fix this by taking the appropriate sample in the case of process wide
timers.

This probably doesn't matter much in practice because, at this stage, the
thread is the last one in the group and we reached exit_notify().  This
implies that we called exit_itimers() and there should be no more timers
to handle for that task.

So this is likely dead code anyway but let's fix the current logic
and the warning that came along:

    kernel/posix-cpu-timers.c: In function 'posix_cpu_timer_schedule':
    kernel/posix-cpu-timers.c:1127: warning: 'now' may be used uninitialized in this function

Then we can start to think further about cleaning up that code.

Reported-by: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Chen Gang <gang.chen@asianux.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Chen Gang <gang.chen@asianux.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Cc: Olivier Langlois <olivier@trillion01.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
kernel/posix-cpu-timers.c