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author | Oleg Nesterov <oleg@redhat.com> | 2012-10-26 19:46:06 +0200 |
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committer | Tejun Heo <tj@kernel.org> | 2012-10-26 14:27:49 -0700 |
commit | 5d8f72b55c275677865de670fa147ed318191d81 (patch) | |
tree | 58f4f571440f412861a232ed0c5753771e5a6e58 /include/linux/freezer.h | |
parent | ead5c473712eb26db792b18a4dc98fdb312883fe (diff) | |
download | linux-stable-5d8f72b55c275677865de670fa147ed318191d81.tar.gz linux-stable-5d8f72b55c275677865de670fa147ed318191d81.tar.bz2 linux-stable-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 'include/linux/freezer.h')
-rw-r--r-- | include/linux/freezer.h | 7 |
1 files changed, 3 insertions, 4 deletions
diff --git a/include/linux/freezer.h b/include/linux/freezer.h index ee899329e65a..8039893bc3ec 100644 --- a/include/linux/freezer.h +++ b/include/linux/freezer.h @@ -134,10 +134,9 @@ static inline bool freezer_should_skip(struct task_struct *p) } /* - * These macros are intended to be used whenever you want allow a task that's - * sleeping in TASK_UNINTERRUPTIBLE or TASK_KILLABLE state to be frozen. Note - * that neither return any clear indication of whether a freeze event happened - * while in this function. + * These macros are intended to be used whenever you want allow a sleeping + * task to be frozen. Note that neither return any clear indication of + * whether a freeze event happened while in this function. */ /* Like schedule(), but should not block the freezer. */ |