From e26796066fdf929cbba22dabb801808f986acdb9 Mon Sep 17 00:00:00 2001 From: Michal Hocko Date: Fri, 25 Mar 2016 14:20:41 -0700 Subject: [PATCH] oom: make oom_reaper freezable After "oom: clear TIF_MEMDIE after oom_reaper managed to unmap the address space" oom_reaper will call exit_oom_victim on the target task after it is done. This might however race with the PM freezer: CPU0 CPU1 CPU2 freeze_processes try_to_freeze_tasks # Allocation request out_of_memory oom_killer_disable wake_oom_reaper(P1) __oom_reap_task exit_oom_victim(P1) wait_event(oom_victims==0) [...] do_exit(P1) perform IO/interfere with the freezer which breaks the oom_killer_disable semantic. We no longer have a guarantee that the oom victim won't interfere with the freezer because it might be anywhere on the way to do_exit while the freezer thinks the task has already terminated. It might trigger IO or touch devices which are frozen already. In order to close this race, make the oom_reaper thread freezable. This will work because a) already running oom_reaper will block freezer to enter the quiescent state b) wake_oom_reaper will not wake up the reaper after it has been frozen c) the only way to call exit_oom_victim after try_to_freeze_tasks is from the oom victim's context when we know the further interference shouldn't be possible Signed-off-by: Michal Hocko Cc: Tetsuo Handa Cc: David Rientjes Cc: Mel Gorman Cc: Oleg Nesterov Cc: Hugh Dickins Cc: Rik van Riel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/oom_kill.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/oom_kill.c b/mm/oom_kill.c index a49638f41e45..8cc55f0f0e5c 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -525,6 +525,8 @@ static void oom_reap_task(struct task_struct *tsk) static int oom_reaper(void *unused) { + set_freezable(); + while (true) { struct task_struct *tsk = NULL; -- 2.20.1