From: Sultan Alsawaf <sultan@xxxxxxxxxxxxxxx> Subject: mm: mark the OOM reaper thread as freezable The OOM reaper alters user address space which might theoretically alter the snapshot if reaping is allowed to happen after the freezer quiescent state. To this end, the reaper kthread uses wait_event_freezable() while waiting for any work so that it cannot run while the system freezes. However, the current implementation doesn't respect the freezer because all kernel threads are created with the PF_NOFREEZE flag, so they are automatically excluded from freezing operations. This means that the OOM reaper can race with system snapshotting if it has work to do while the system is being frozen. Fix this by adding a set_freezable() call which will clear the PF_NOFREEZE flag and thus make the OOM reaper visible to the freezer. Please note that the OOM reaper altering the snapshot this way is mostly a theoretical concern and has not been observed in practice. Link: https://lkml.kernel.org/r/20210921165758.6154-1-sultan@xxxxxxxxxxxxxxx Link: https://lkml.kernel.org/r/20210918233920.9174-1-sultan@xxxxxxxxxxxxxxx Fixes: aac453635549 ("mm, oom: introduce oom reaper") Signed-off-by: Sultan Alsawaf <sultan@xxxxxxxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/oom_kill.c | 2 ++ 1 file changed, 2 insertions(+) --- a/mm/oom_kill.c~mm-mark-the-oom-reaper-thread-as-freezable +++ a/mm/oom_kill.c @@ -641,6 +641,8 @@ done: static int oom_reaper(void *unused) { + set_freezable(); + while (true) { struct task_struct *tsk = NULL; _
