On Sun 16-07-17 19:59:51, Tetsuo Handa wrote: > Since the whole memory reclaim path has never been designed to handle the > scheduling priority inversions, those locations which are assuming that > execution of some code path shall eventually complete without using > synchronization mechanisms can get stuck (livelock) due to scheduling > priority inversions, for CPU time is not guaranteed to be yielded to some > thread doing such code path. > > mutex_trylock() in __alloc_pages_may_oom() (waiting for oom_lock) and > schedule_timeout_killable(1) in out_of_memory() (already held oom_lock) is > one of such locations, and it was demonstrated using artificial stressing > that the system gets stuck effectively forever because SCHED_IDLE priority > thread is unable to resume execution at schedule_timeout_killable(1) if > a lot of !SCHED_IDLE priority threads are wasting CPU time [1].
I do not understand this. All the contending tasks will go and sleep for 1s. How can they preempt the lock holder? -- Michal Hocko SUSE Labs
