Commit e2679606 authored by Michal Hocko's avatar Michal Hocko Committed by Linus Torvalds
Browse files

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
  				# Allocation request
				  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
	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: default avatarMichal Hocko <>
Cc: Tetsuo Handa <>
Cc: David Rientjes <>
Cc: Mel Gorman <>
Cc: Oleg Nesterov <>
Cc: Hugh Dickins <>
Cc: Rik van Riel <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 29c696e1
......@@ -525,6 +525,8 @@ static void oom_reap_task(struct task_struct *tsk)
static int oom_reaper(void *unused)
while (true) {
struct task_struct *tsk = NULL;
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