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SubjectRe: [PATCH] mm,page_alloc: PF_WQ_WORKER threads must sleep at should_reclaim_retry().
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On 2018/08/24 9:31, Tetsuo Handa wrote:
> For now, I don't think we need to add af5679fbc669f31f to the list for
> CVE-2016-10723, for af5679fbc669f31f might cause premature next OOM victim
> selection (especially with CONFIG_PREEMPT=y kernels) due to
>
> __alloc_pages_may_oom(): oom_reap_task():
>
> mutex_trylock(&oom_lock) succeeds.
> get_page_from_freelist() fails.
> Preempted to other process.
> oom_reap_task_mm() succeeds.
> Sets MMF_OOM_SKIP.
> Returned from preemption.
> Finds that MMF_OOM_SKIP was already set.
> Selects next OOM victim and kills it.
> mutex_unlock(&oom_lock) is called.
>
> race window like described as
>
> Tetsuo was arguing that at least MMF_OOM_SKIP should be set under the lock
> to prevent from races when the page allocator didn't manage to get the
> freed (reaped) memory in __alloc_pages_may_oom but it sees the flag later
> on and move on to another victim. Although this is possible in principle
> let's wait for it to actually happen in real life before we make the
> locking more complex again.
>
> in that commit.
>

Yes, that race window is real. We can needlessly select next OOM victim.
I think that af5679fbc669f31f was too optimistic.

[ 278.147280] Out of memory: Kill process 9943 (a.out) score 919 or sacrifice child
[ 278.148927] Killed process 9943 (a.out) total-vm:4267252kB, anon-rss:3430056kB, file-rss:0kB, shmem-rss:0kB
[ 278.151586] vmtoolsd invoked oom-killer: gfp_mask=0x6200ca(GFP_HIGHUSER_MOVABLE), nodemask=(null), order=0, oom_score_adj=0
[ 278.156642] vmtoolsd cpuset=/ mems_allowed=0
[ 278.158884] CPU: 2 PID: 8916 Comm: vmtoolsd Kdump: loaded Not tainted 4.19.0-rc2+ #465
[ 278.162252] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 05/19/2017
[ 278.165499] Call Trace:
[ 278.166693] dump_stack+0x99/0xdc
[ 278.167922] dump_header+0x70/0x2fa
[ 278.169414] oom_reaper: reaped process 9943 (a.out), now anon-rss:0kB, file-rss:0kB, shmem-rss:0kB
[ 278.169629] ? _raw_spin_unlock_irqrestore+0x6a/0x8c
[ 278.169633] oom_kill_process+0x2ee/0x380
[ 278.169635] out_of_memory+0x136/0x540
[ 278.169636] ? out_of_memory+0x1fc/0x540
[ 278.169640] __alloc_pages_slowpath+0x986/0xce4
[ 278.169641] ? get_page_from_freelist+0x16b/0x1600
[ 278.169646] __alloc_pages_nodemask+0x398/0x3d0
[ 278.180594] alloc_pages_current+0x65/0xb0
[ 278.182173] __page_cache_alloc+0x154/0x190
[ 278.184200] ? pagecache_get_page+0x27/0x250
[ 278.185410] filemap_fault+0x4df/0x880
[ 278.186282] ? filemap_fault+0x31b/0x880
[ 278.187395] ? xfs_ilock+0x1bd/0x220
[ 278.188264] ? __xfs_filemap_fault+0x76/0x270
[ 278.189268] ? down_read_nested+0x48/0x80
[ 278.190229] ? xfs_ilock+0x1bd/0x220
[ 278.191061] __xfs_filemap_fault+0x89/0x270
[ 278.192059] xfs_filemap_fault+0x27/0x30
[ 278.192967] __do_fault+0x1f/0x70
[ 278.193777] __handle_mm_fault+0xfbd/0x1470
[ 278.194743] handle_mm_fault+0x1f2/0x400
[ 278.195679] ? handle_mm_fault+0x47/0x400
[ 278.196618] __do_page_fault+0x217/0x4b0
[ 278.197504] do_page_fault+0x3c/0x21e
[ 278.198303] ? page_fault+0x8/0x30
[ 278.199092] page_fault+0x1e/0x30
[ 278.199821] RIP: 0033:0x7f2322ebbfb0
[ 278.200605] Code: Bad RIP value.
[ 278.201370] RSP: 002b:00007ffda96e7648 EFLAGS: 00010246
[ 278.202518] RAX: 0000000000000000 RBX: 00007f23220f26b0 RCX: 0000000000000010
[ 278.204280] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007f2321ecfb5b
[ 278.205838] RBP: 0000000002504b70 R08: 00007f2321ecfb60 R09: 000000000250bd20
[ 278.207426] R10: 383836312d646c69 R11: 0000000000000000 R12: 00007ffda96e76b0
[ 278.208982] R13: 00007f2322ea8540 R14: 000000000250ba90 R15: 00007f2323173920
[ 278.210840] Mem-Info:
[ 278.211462] active_anon:18629 inactive_anon:2390 isolated_anon:0
[ 278.211462] active_file:19 inactive_file:1565 isolated_file:0
[ 278.211462] unevictable:0 dirty:0 writeback:0 unstable:0
[ 278.211462] slab_reclaimable:5820 slab_unreclaimable:8964
[ 278.211462] mapped:2128 shmem:2493 pagetables:1826 bounce:0
[ 278.211462] free:878043 free_pcp:909 free_cma:0
[ 278.218830] Node 0 active_anon:74516kB inactive_anon:9560kB active_file:76kB inactive_file:6260kB unevictable:0kB isolated(anon):0kB isolated(file):0kB mapped:8512kB dirty:0kB writeback:0kB shmem:9972kB shmem_thp: 0kB shmem_pmdmapped: 0kB anon_thp: 43008kB writeback_tmp:0kB unstable:0kB all_unreclaimable? yes
[ 278.224997] Node 0 DMA free:15888kB min:288kB low:360kB high:432kB active_anon:32kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:15988kB managed:15904kB mlocked:0kB kernel_stack:0kB pagetables:4kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
[ 278.230602] lowmem_reserve[]: 0 2663 3610 3610
[ 278.231887] Node 0 DMA32 free:2746332kB min:49636kB low:62044kB high:74452kB active_anon:2536kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:3129216kB managed:2749920kB mlocked:0kB kernel_stack:0kB pagetables:4kB bounce:0kB free_pcp:1500kB local_pcp:0kB free_cma:0kB
[ 278.238291] lowmem_reserve[]: 0 0 947 947
[ 278.239270] Node 0 Normal free:749952kB min:17652kB low:22064kB high:26476kB active_anon:72816kB inactive_anon:9560kB active_file:264kB inactive_file:5556kB unevictable:0kB writepending:4kB present:1048576kB managed:969932kB mlocked:0kB kernel_stack:5328kB pagetables:7092kB bounce:0kB free_pcp:2132kB local_pcp:64kB free_cma:0kB
[ 278.245895] lowmem_reserve[]: 0 0 0 0
[ 278.246820] Node 0 DMA: 0*4kB 0*8kB 0*16kB 1*32kB (U) 2*64kB (U) 1*128kB (U) 1*256kB (U) 0*512kB 1*1024kB (U) 1*2048kB (M) 3*4096kB (M) = 15904kB
[ 278.249659] Node 0 DMA32: 7*4kB (U) 8*8kB (UM) 8*16kB (U) 8*32kB (U) 8*64kB (U) 6*128kB (U) 7*256kB (UM) 7*512kB (UM) 3*1024kB (UM) 2*2048kB (M) 667*4096kB (UM) = 2746332kB
[ 278.253054] Node 0 Normal: 4727*4kB (UME) 3423*8kB (UME) 1679*16kB (UME) 704*32kB (UME) 253*64kB (UME) 107*128kB (UME) 38*256kB (M) 16*512kB (M) 10*1024kB (M) 9*2048kB (M) 141*4096kB (M) = 749700kB
[ 278.257158] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
[ 278.259018] 4125 total pagecache pages
[ 278.259896] 0 pages in swap cache
[ 278.260745] Swap cache stats: add 0, delete 0, find 0/0
[ 278.261934] Free swap = 0kB
[ 278.262750] Total swap = 0kB
[ 278.263483] 1048445 pages RAM
[ 278.264216] 0 pages HighMem/MovableOnly
[ 278.265077] 114506 pages reserved
[ 278.265971] Tasks state (memory values in pages):
[ 278.267118] [ pid ] uid tgid total_vm rss pgtables_bytes swapents oom_score_adj name
[ 278.269090] [ 2846] 0 2846 267 171 32768 0 0 none
[ 278.271221] [ 4891] 0 4891 9772 856 110592 0 0 systemd-journal
[ 278.273253] [ 6610] 0 6610 10811 261 114688 0 -1000 systemd-udevd
[ 278.275197] [ 6709] 0 6709 13880 112 131072 0 -1000 auditd
[ 278.277067] [ 7388] 0 7388 3307 52 69632 0 0 rngd
[ 278.278880] [ 7393] 0 7393 24917 403 184320 0 0 VGAuthService
[ 278.280864] [ 7510] 70 7510 15043 102 155648 0 0 avahi-daemon
[ 278.282898] [ 7555] 0 7555 5420 372 81920 0 0 irqbalance
[ 278.284836] [ 7563] 0 7563 6597 83 102400 0 0 systemd-logind
[ 278.286959] [ 7565] 81 7565 14553 157 167936 0 -900 dbus-daemon
[ 278.288985] [ 8286] 70 8286 15010 98 151552 0 0 avahi-daemon
[ 278.290958] [ 8731] 0 8731 74697 999 270336 0 0 vmtoolsd
[ 278.293008] [ 8732] 999 8732 134787 1730 274432 0 0 polkitd
[ 278.294906] [ 8733] 0 8733 55931 467 274432 0 0 abrtd
[ 278.296774] [ 8734] 0 8734 55311 354 266240 0 0 abrt-watch-log
[ 278.298839] [ 8774] 0 8774 31573 155 106496 0 0 crond
[ 278.300810] [ 8790] 0 8790 89503 5482 421888 0 0 firewalld
[ 278.302727] [ 8916] 0 8916 45262 211 204800 0 0 vmtoolsd
[ 278.304841] [ 9230] 0 9230 26877 507 229376 0 0 dhclient
[ 278.306733] [ 9333] 0 9333 87236 451 528384 0 0 nmbd
[ 278.308554] [ 9334] 0 9334 28206 257 253952 0 -1000 sshd
[ 278.310431] [ 9335] 0 9335 143457 3260 430080 0 0 tuned
[ 278.312278] [ 9337] 0 9337 55682 2442 200704 0 0 rsyslogd
[ 278.314188] [ 9497] 0 9497 24276 170 233472 0 0 login
[ 278.316038] [ 9498] 0 9498 27525 33 73728 0 0 agetty
[ 278.317918] [ 9539] 0 9539 104864 581 659456 0 0 smbd
[ 278.319738] [ 9590] 0 9590 103799 555 610304 0 0 smbd-notifyd
[ 278.321918] [ 9591] 0 9591 103797 555 602112 0 0 cleanupd
[ 278.323935] [ 9592] 0 9592 104864 580 610304 0 0 lpqd
[ 278.325835] [ 9596] 0 9596 28894 129 90112 0 0 bash
[ 278.327663] [ 9639] 0 9639 28833 474 249856 0 0 sendmail
[ 278.329550] [ 9773] 51 9773 26644 411 229376 0 0 sendmail
[ 278.331527] Out of memory: Kill process 8790 (firewalld) score 5 or sacrifice child
[ 278.333267] Killed process 8790 (firewalld) total-vm:358012kB, anon-rss:21928kB, file-rss:0kB, shmem-rss:0kB
[ 278.336430] oom_reaper: reaped process 8790 (firewalld), now anon-rss:0kB, file-rss:0kB, shmem-rss:0kB

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