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| author | Frederic Weisbecker <fweisbec@gmail.com> | 2013-10-11 17:41:11 +0200 |
|---|---|---|
| committer | Frederic Weisbecker <fweisbec@gmail.com> | 2013-12-09 16:53:51 +0100 |
| commit | 50875788a1d4a3f662a27ed13cd05282d835939a (patch) | |
| tree | 254cb6e105b576170aac22c195289de7b1998749 | |
| parent | posix-timers: Consolidate posix_cpu_clock_get() (diff) | |
| download | linux-50875788a1d4a3f662a27ed13cd05282d835939a.tar.xz linux-50875788a1d4a3f662a27ed13cd05282d835939a.zip | |
posix-timers: Use sighand lock instead of tasklist_lock for task clock sample
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>
| -rw-r--r-- | kernel/posix-cpu-timers.c | 16 |
1 files changed, 13 insertions, 3 deletions
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c index 03c5d6c3e614..71a07699a36b 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) |