On Mon 25-06-18 15:03:40, peter enderborg wrote: > On 06/20/2018 01:55 PM, Michal Hocko wrote: > > On Wed 20-06-18 20:20:38, Tetsuo Handa wrote: > >> Sleeping with oom_lock held can cause AB-BA lockup bug because > >> __alloc_pages_may_oom() does not wait for oom_lock. Since > >> blocking_notifier_call_chain() in out_of_memory() might sleep, sleeping > >> with oom_lock held is currently an unavoidable problem. > > Could you be more specific about the potential deadlock? Sleeping while > > holding oom lock is certainly not nice but I do not see how that would > > result in a deadlock assuming that the sleeping context doesn't sleep on > > the memory allocation obviously. > > It is a mutex you are supposed to be able to sleep. It's even exported. What do you mean? oom_lock is certainly not exported for general use. It is not local to oom_killer.c just because it is needed in other _mm_ code. > >> As a preparation for not to sleep with oom_lock held, this patch brings > >> OOM notifier callbacks to outside of OOM killer, with two small behavior > >> changes explained below. > > Can we just eliminate this ugliness and remove it altogether? We do not > > have that many notifiers. Is there anything fundamental that would > > prevent us from moving them to shrinkers instead? > > > @Hocko Do you remember the lowmemorykiller from android? Some things > might not be the right thing for shrinkers. Just that lmk did it wrong doesn't mean others have to follow. -- Michal Hocko SUSE Labs
