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authorOleg Nesterov <oleg@redhat.com>2012-10-26 21:46:06 +0400
committerTejun Heo <tj@kernel.org>2012-10-27 01:27:49 +0400
commit5d8f72b55c275677865de670fa147ed318191d81 (patch)
tree58f4f571440f412861a232ed0c5753771e5a6e58 /include/linux/freezer.h
parentead5c473712eb26db792b18a4dc98fdb312883fe (diff)
downloadlinux-5d8f72b55c275677865de670fa147ed318191d81.tar.xz
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.h7
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. */