diff options
| author | Oleg Nesterov <oleg@redhat.com> | 2012-10-26 19:46:06 +0200 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2012-10-26 23:27:49 +0200 |
| commit | 5d8f72b55c275677865de670fa147ed318191d81 (patch) | |
| tree | 58f4f571440f412861a232ed0c5753771e5a6e58 /kernel/power | |
| parent | cgroup_freezer: don't use cgroup_lock_live_group() (diff) | |
| download | linux-5d8f72b55c275677865de670fa147ed318191d81.tar.xz linux-5d8f72b55c275677865de670fa147ed318191d81.zip | |
freezer: change ptrace_stop/do_signal_stop to use freezable_schedule()
try_to_freeze_tasks() and cgroup_freezer rely on scheduler locks
to ensure that a task doing STOPPED/TRACED -> RUNNING transition
can't escape freezing. This mostly works, but ptrace_stop() does
not necessarily call schedule(), it can change task->state back to
RUNNING and check freezing() without any lock/barrier in between.
We could add the necessary barrier, but this patch changes
ptrace_stop() and do_signal_stop() to use freezable_schedule().
This fixes the race, freezer_count() and freezer_should_skip()
carefully avoid the race.
And this simplifies the code, try_to_freeze_tasks/update_if_frozen
no longer need to use task_is_stopped_or_traced() checks with the
non trivial assumptions. We can rely on the mechanism which was
specially designed to mark the sleeping task as "frozen enough".
v2: As Tejun pointed out, we can also change get_signal_to_deliver()
and move try_to_freeze() up before 'relock' label.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel/power')
| -rw-r--r-- | kernel/power/process.c | 13 |
1 files changed, 1 insertions, 12 deletions
diff --git a/kernel/power/process.c b/kernel/power/process.c index 87da817f9e13..d5a258b60c6f 100644 --- a/kernel/power/process.c +++ b/kernel/power/process.c @@ -48,18 +48,7 @@ static int try_to_freeze_tasks(bool user_only) if (p == current || !freeze_task(p)) continue; - /* - * Now that we've done set_freeze_flag, don't - * perturb a task in TASK_STOPPED or TASK_TRACED. - * It is "frozen enough". If the task does wake - * up, it will immediately call try_to_freeze. - * - * Because freeze_task() goes through p's scheduler lock, it's - * guaranteed that TASK_STOPPED/TRACED -> TASK_RUNNING - * transition can't race with task state testing here. - */ - if (!task_is_stopped_or_traced(p) && - !freezer_should_skip(p)) + if (!freezer_should_skip(p)) todo++; } while_each_thread(g, p); read_unlock(&tasklist_lock); |