On Wed 17-02-16 23:31:25, Tetsuo Handa wrote: > Currently, oom_scan_process_thread() returns OOM_SCAN_ABORT when there is > a thread which is exiting. But it is possible that that thread is blocked > at down_read(&mm->mmap_sem) in exit_mm() called from do_exit() whereas > one of threads sharing that memory is doing a GFP_KERNEL allocation > between down_write(&mm->mmap_sem) and up_write(&mm->mmap_sem) > (e.g. mmap()). > > ---------- > T1 T2 > Calls mmap() > Calls _exit(0) > Arrives at vm_mmap_pgoff() > Arrives at do_exit() > Gets PF_EXITING via exit_signals() > Calls down_write(&mm->mmap_sem) > Calls do_mmap_pgoff() > Calls down_read(&mm->mmap_sem) from exit_mm() > Calls out of memory via a GFP_KERNEL allocation but > oom_scan_process_thread(T1) returns OOM_SCAN_ABORT > ---------- > > down_read(&mm->mmap_sem) by T1 is waiting for up_write(&mm->mmap_sem) by > T2 while oom_scan_process_thread() by T2 is waiting for T1 to set > T1->mm = NULL. Under such situation, the OOM killer does not choose > a victim, which results in silent OOM livelock problem. > > This patch changes oom_scan_process_thread() not to return OOM_SCAN_ABORT > when there is a thread which is exiting. Thank you for the updated changelog. This makes much more sense now. This problem exists for quite some time but I would be hesitant to mark it for stable because the side effects are quite hard to evaluate. We could e.g. see a premature OOM killer invocation while the currently exiting task just didn't get to finish and release its mm. > Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> > Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> > --- > mm/oom_kill.c | 3 --- > 1 file changed, 3 deletions(-) > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index cf87153..6e6abaf 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -292,9 +292,6 @@ enum oom_scan_t oom_scan_process_thread(struct oom_control *oc, > if (oom_task_origin(task)) > return OOM_SCAN_SELECT; > > - if (task_will_free_mem(task) && !is_sysrq_oom(oc)) > - return OOM_SCAN_ABORT; > - > return OOM_SCAN_OK; > } > > -- > 1.8.3.1 -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>