On Fri 16-06-17 19:27:19, Tetsuo Handa wrote: > Michal Hocko wrote: > > On Fri 16-06-17 09:54:34, Tetsuo Handa wrote: > > [...] > > > And the patch you proposed is broken. > > > > Thanks for your testing! > > > > > ---------- > > > [ 161.846202] Out of memory: Kill process 6331 (a.out) score 999 or > > > sacrifice child > > > [ 161.850327] Killed process 6331 (a.out) total-vm:4172kB, > > > anon-rss:84kB, file-rss:0kB, shmem-rss:0kB > > > [ 161.858503] ------------[ cut here ]------------ > > > [ 161.861512] kernel BUG at mm/memory.c:1381! > > > > BUG_ON(addr >= end) suggests our vma has trimmed. I guess I see what is > > going on here. > > __oom_reap_task_mm exit_mmap > > free_pgtables > > up_write(mm->mmap_sem) > > down_read_trylock(&mm->mmap_sem) > > remove_vma > > unmap_page_range > > > > So we need to extend the mmap_sem coverage. See the updated diff (not > > the full proper patch yet). > > That diff is still wrong. We need to prevent __oom_reap_task_mm() from calling > unmap_page_range() when __mmput() already called exit_mm(), by > setting/checking > MMF_OOM_SKIP like shown below.
Care to explain why? [...] > Since the OOM reaper does not reap hugepages, khugepaged_exit() part could be > safe. I think you are mixing hugetlb and THP pages here. khugepaged_exit is about later and we do unmap those. > But ksm_exit() part might interfere. How? > If it is guaranteed to be safe, > what will go wrong if we move uprobe_clear_state()/exit_aio()/ksm_exit() etc. > to just before mmdrop() (i.e. after setting MMF_OOM_SKIP) ? I do not see why those matter and why they should be any special. Unless I miss anything we really do only care about page table tear down and the address space modification. They do none of that. -- Michal Hocko SUSE Labs
