Michal Hocko wrote: > 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? I don't know. Your updated diff is causing below oops. ---------- [ 90.621890] Out of memory: Kill process 2671 (a.out) score 999 or sacrifice child [ 90.624636] Killed process 2671 (a.out) total-vm:4172kB, anon-rss:84kB, file-rss:0kB, shmem-rss:0kB [ 90.861308] general protection fault: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC [ 90.863695] Modules linked in: coretemp pcspkr sg vmw_vmci shpchp i2c_piix4 sd_mod ata_generic pata_acpi serio_raw vmwgfx drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ttm mptspi scsi_transport_spi mptscsih ahci mptbase libahci drm e1000 ata_piix i2c_core libata ipv6 [ 90.870672] CPU: 2 PID: 47 Comm: oom_reaper Not tainted 4.12.0-rc5+ #128 [ 90.872929] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/02/2015 [ 90.875995] task: ffff88007b6cd2c0 task.stack: ffff88007b6d0000 [ 90.878290] RIP: 0010:__oom_reap_task_mm+0xa1/0x160 [ 90.880242] RSP: 0018:ffff88007b6d3df0 EFLAGS: 00010202 [ 90.882240] RAX: 6b6b6b6b6b6b6b6b RBX: ffff880077b8cd40 RCX: 0000000000000000 [ 90.884612] RDX: ffff88007b6d3e18 RSI: ffff880077b8cd40 RDI: ffff88007b6d3df0 [ 90.887001] RBP: ffff88007b6d3e98 R08: ffff88007b6cdb08 R09: ffff88007b6cdad0 [ 90.889702] R10: 0000000000000000 R11: 000000009213dd65 R12: ffff880077b8ce00 [ 90.892973] R13: ffff880076f48040 R14: 6b6b6b6b6b6b6b6b R15: ffff880077b8cd40 [ 90.895765] FS: 0000000000000000(0000) GS:ffff88007c600000(0000) knlGS:0000000000000000 [ 90.899015] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 90.901462] CR2: 00007feeae35ac80 CR3: 0000000076e21000 CR4: 00000000001406e0 [ 90.904019] Call Trace: [ 90.905518] ? process_timeout+0x1/0x10 [ 90.907280] oom_reaper+0xa2/0x1b0 [ 90.908946] ? wake_up_bit+0x30/0x30 [ 90.911391] kthread+0x10d/0x140 [ 90.913003] ? __oom_reap_task_mm+0x160/0x160 [ 90.914936] ? kthread_create_on_node+0x60/0x60 [ 90.916733] ret_from_fork+0x27/0x40 [ 90.918307] Code: c3 e8 54 82 f1 ff f0 80 8b 7a 04 00 00 40 48 8d bd 58 ff ff ff 48 83 c9 ff 31 d2 48 89 de e8 57 12 03 00 4c 8b 33 4d 85 f6 74 3b <49> 8b 46 50 a9 00 24 40 00 75 27 49 83 be 90 00 00 00 00 74 04 [ 90.923922] RIP: __oom_reap_task_mm+0xa1/0x160 RSP: ffff88007b6d3df0 [ 90.929583] ---[ end trace 20f6ec27ed25c461 ]--- ---------- It is you who should explain why. I found my patch via trial and error. > [...] > > > 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. OK. > > > But ksm_exit() part might interfere. > > How? Why you think it does not interfere? Please explain it in your patch description because your patch is trying to do a tricky thing. I'm not a MM person. I just suspect what you think no problem. > > > 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. I think the patch I posted at http://lkml.kernel.org/r/201706162122.ACE95321.tOFLOOVFFHMSJQ@xxxxxxxxxxxxxxxxxxx will be safer, and you agree that a solution which is fully contained inside the oom proper would be preferable. Thus, let's start checking that patch. -- 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>
