From: Oleg Nesterov Date: Fri, 26 Oct 2012 17:46:06 +0000 (+0200) Subject: freezer: change ptrace_stop/do_signal_stop to use freezable_schedule() X-Git-Tag: omap-for-v3.8/fixes-for-merge-window-v4-signed~57^2~48 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5d8f72b55c275677865de670fa147ed318191d81;p=pandora-kernel.git 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 Signed-off-by: Tejun Heo --- Reading git-diff-tree failed