The patch titled
Subject: oom: make oom_reaper freezable
has been added to the -mm tree. Its filename is
oom-make-oom_reaper-freezable.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/oom-make-oom_reaper-freezable.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/oom-make-oom_reaper-freezable.patch
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From: Michal Hocko <mhocko@xxxxxxxx>
Subject: 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 <mhocko@xxxxxxxx>
Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/oom_kill.c | 2 ++
1 file changed, 2 insertions(+)
diff -puN mm/oom_kill.c~oom-make-oom_reaper-freezable mm/oom_kill.c
--- a/mm/oom_kill.c~oom-make-oom_reaper-freezable
+++ a/mm/oom_kill.c
@@ -525,6 +525,8 @@ static void oom_reap_task(struct task_st
static int oom_reaper(void *unused)
{
+ set_freezable();
+
while (true) {
struct task_struct *tsk = NULL;
_
Patches currently in -mm which might be from mhocko@xxxxxxxx are
mm-vmscan-make-zone_reclaimable_pages-more-precise.patch
mm-oom-introduce-oom-reaper.patch
oom-reaper-handle-mlocked-pages.patch
oom-clear-tif_memdie-after-oom_reaper-managed-to-unmap-the-address-space.patch
mm-oom_reaper-report-success-failure.patch
mm-oom_reaper-report-success-failure-fix-2.patch
mm-oom_reaper-implement-oom-victims-queuing.patch
oom-make-oom_reaper-freezable.patch
mm-oom-rework-oom-detection.patch
mm-throttle-on-io-only-when-there-are-too-many-dirty-and-writeback-pages.patch
mm-use-watermak-checks-for-__gfp_repeat-high-order-allocations.patch
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