• Michal Hocko's avatar
    mm, oom: do not fail __GFP_NOFAIL allocation if oom killer is disabled · e009d5dc
    Michal Hocko authored
    Tetsuo Handa has pointed out that __GFP_NOFAIL allocations might fail
    after OOM killer is disabled if the allocation is performed by a kernel
    thread.  This behavior was introduced from the very beginning by
    7f33d49a ("mm, PM/Freezer: Disable OOM killer when tasks are frozen").
     This means that the basic contract for the allocation request is broken
    and the context requesting such an allocation might blow up unexpectedly.
    
    There are basically two ways forward.
    
    1) move oom_killer_disable after kernel threads are frozen.  This has a
       risk that the OOM victim wouldn't be able to finish because it would
       depend on an already frozen kernel thread.  This would be really tricky
       to debug.
    
    2) do not fail GFP_NOFAIL allocation no matter what and risk a
       potential Freezable kernel threads will loop and fail the suspend.
       Incidental allocations after kernel threads are frozen will at least
       dump a warning - if we are lucky and the serial console is still active
       of course...
    
    This patch implements the later option because it is safer.  We would see
    warning rather than allocation failures for the kernel threads which would
    blow up otherwise and have a higher chances to identify __GFP_NOFAIL users
    from deeper pm code.
    Signed-off-by: 's avatarMichal Hocko <mhocko@suse.cz>
    Acked-by: 's avatarDavid Rientjes <rientjes@gooogle.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
    Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
    Signed-off-by: 's avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: 's avatarLinus Torvalds <torvalds@linux-foundation.org>
    e009d5dc
page_alloc.c 182 KB