Messages in this thread Patch in this message | | | From | Frederic Weisbecker <> | Subject | [RFC PATCH 07/10] posix-timers: Use sighand lock instead of tasklist_lock for task clock sample | Date | Sat, 12 Oct 2013 21:06:23 +0200 |
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There is no need for the tasklist_lock just to take a process wide clock sample.
All we need is to get a coherent sample that doesn't race with exit() and exec():
* exit() may be concurrently reaping a task and flushing its time
* sighand is unstable under exit() and exec(), and the latter also result in group leader that can change
To protect against these, locking the target's sighand is enough.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Kosaki Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Andrew Morton <akpm@linux-foundation.org> --- kernel/posix-cpu-timers.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c index 7117f6d..cd56e71 100644 --- a/kernel/posix-cpu-timers.c +++ b/kernel/posix-cpu-timers.c @@ -271,12 +271,22 @@ static int posix_cpu_clock_get_task(struct task_struct *tsk, if (same_thread_group(tsk, current)) err = cpu_clock_sample(which_clock, tsk, &rtn); } else { - read_lock(&tasklist_lock); + unsigned long flags; + struct sighand_struct *sighand; - if (tsk->sighand && (tsk == current || thread_group_leader(tsk))) + /* + * while_each_thread() is not yet entirely RCU safe, + * keep locking the group while sampling process + * clock for now. + */ + sighand = lock_task_sighand(tsk, &flags); + if (!sighand) + return err; + + if (tsk == current || thread_group_leader(tsk)) err = cpu_clock_sample_group(which_clock, tsk, &rtn); - read_unlock(&tasklist_lock); + unlock_task_sighand(tsk, &flags); } if (!err) -- 1.8.3.1
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