On 06/25/2018 03:07 PM, Michal Hocko wrote: > 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. > It is in the oom.h file include/linux/oom.h, if it that sensitive it should be in mm/ and a documented note about the special rules. It is only used in drivers/tty/sysrq.c and that be replaced by a help function in mm that do the oom stuff. >>>> 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. > If all you have is a hammer, everything looks like a nail. (I don’t argument that it was right) But if you don’t have a way to interact with the memory system we will get attempts like lmk. Oom notifiers and vmpressure is for this task better than shrinkers.
