Manish Jaggi noticed that running LTP oom01/oom02 ltp tests with high core
count causes random kernel panics when an OOM victim which consumed memory
in a way the OOM reaper does not help was selected by the OOM killer [1].
----------
oom02 0 TINFO : start OOM testing for mlocked pages.
oom02 0 TINFO : expected victim is 4578.
oom02 0 TINFO : thread (ffff8b0e71f0), allocating 3221225472 bytes.
oom02 0 TINFO : thread (ffff8b8e71f0), allocating 3221225472 bytes.
(...snipped...)
oom02 0 TINFO : thread (ffff8a0e71f0), allocating 3221225472 bytes.
[ 364.737486] oom02:4583 invoked oom-killer: gfp_mask=0x16080c0(GFP_KERNEL|__GFP_ZERO|__GFP_NOTRACK), nodemask=1, order=0, oom_score_adj=0
(...snipped...)
[ 365.036127] [ pid ] uid tgid total_vm rss nr_ptes nr_pmds swapents oom_score_adj name
[ 365.044691] [ 1905] 0 1905 3236 1714 10 4 0 0 systemd-journal
[ 365.054172] [ 1908] 0 1908 20247 590 8 4 0 0 lvmetad
[ 365.062959] [ 2421] 0 2421 3241 878 9 3 0 -1000 systemd-udevd
[ 365.072266] [ 3125] 0 3125 3834 719 9 4 0 -1000 auditd
[ 365.080963] [ 3145] 0 3145 1086 630 6 4 0 0 systemd-logind
[ 365.090353] [ 3146] 0 3146 1208 596 7 3 0 0 irqbalance
[ 365.099413] [ 3147] 81 3147 1118 625 5 4 0 -900 dbus-daemon
[ 365.108548] [ 3149] 998 3149 116294 4180 26 5 0 0 polkitd
[ 365.117333] [ 3164] 997 3164 19992 785 9 3 0 0 chronyd
[ 365.126118] [ 3180] 0 3180 55605 7880 29 3 0 0 firewalld
[ 365.135075] [ 3187] 0 3187 87842 3033 26 3 0 0 NetworkManager
[ 365.144465] [ 3290] 0 3290 43037 1224 16 5 0 0 rsyslogd
[ 365.153335] [ 3295] 0 3295 108279 6617 30 3 0 0 tuned
[ 365.161944] [ 3308] 0 3308 27846 676 11 3 0 0 crond
[ 365.170554] [ 3309] 0 3309 3332 616 10 3 0 -1000 sshd
[ 365.179076] [ 3371] 0 3371 27307 364 6 3 0 0 agetty
[ 365.187790] [ 3375] 0 3375 29397 1125 11 3 0 0 login
[ 365.196402] [ 4178] 0 4178 4797 1119 14 4 0 0 master
[ 365.205101] [ 4209] 89 4209 4823 1396 12 4 0 0 pickup
[ 365.213798] [ 4211] 89 4211 4842 1485 12 3 0 0 qmgr
[ 365.222325] [ 4491] 0 4491 27965 1022 8 3 0 0 bash
[ 365.230849] [ 4513] 0 4513 670 365 5 3 0 0 oom02
[ 365.239459] [ 4578] 0 4578 37776030 32890957 64257 138 0 0 oom02
[ 365.248067] Out of memory: Kill process 4578 (oom02) score 952 or sacrifice child
[ 365.255581] Killed process 4578 (oom02) total-vm:151104120kB, anon-rss:131562528kB, file-rss:1300kB, shmem-rss:0kB
[ 365.266829] out_of_memory: Current (4583) has a pending SIGKILL
[ 365.267347] oom_reaper: reaped process 4578 (oom02), now anon-rss:131559616kB, file-rss:0kB, shmem-rss:0kB
[ 365.282658] oom_reaper: reaped process 4583 (oom02), now anon-rss:131561664kB, file-rss:0kB, shmem-rss:0kB
[ 365.283361] oom02:4586 invoked oom-killer: gfp_mask=0x16040c0(GFP_KERNEL|__GFP_COMP|__GFP_NOTRACK), nodemask=1, order=0, oom_score_adj=0
(...snipped...)
[ 365.576164] oom02:4585 invoked oom-killer: gfp_mask=0x16080c0(GFP_KERNEL|__GFP_ZERO|__GFP_NOTRACK), nodemask=1, order=0, oom_score_adj=0
(...snipped...)
[ 365.576298] [ pid ] uid tgid total_vm rss nr_ptes nr_pmds swapents oom_score_adj name
[ 365.576338] [ 2421] 0 2421 3241 878 9 3 0 -1000 systemd-udevd
[ 365.576342] [ 3125] 0 3125 3834 719 9 4 0 -1000 auditd
[ 365.576347] [ 3309] 0 3309 3332 616 10 3 0 -1000 sshd
[ 365.576356] [ 4580] 0 4578 37776030 32890417 64258 138 0 0 oom02
[ 365.576361] Kernel panic - not syncing: Out of memory and no killable processes...
----------
Since commit 696453e66630ad45 ("mm, oom: task_will_free_mem should skip
oom_reaped tasks") changed task_will_free_mem(current) in out_of_memory()
to return false as soon as MMF_OOM_SKIP is set, many threads sharing the
victim's mm were not able to try allocation from memory reserves after the
OOM reaper gave up reclaiming memory.
Until Linux 4.7, we were using
if (current->mm &&
(fatal_signal_pending(current) || task_will_free_mem(current)))
as a condition to try allocation from memory reserves with the risk of OOM
lockup, but reports like [1] were impossible. Linux 4.8+ are regressed
compared to Linux 4.7 due to the risk of needlessly selecting more OOM
victims.
Although commit cd04ae1e2dc8e365 ("mm, oom: do not rely on TIF_MEMDIE for
memory reserves access") mitigated this regression by not requiring each
OOM victim thread to call task_will_free_mem(current), some of OOM victim
threads which are between post __gfp_pfmemalloc_flags(gfp_mask) and pre
mutex_trylock(&oom_lock) (a race window which that commit cannot close)
can call out_of_memory() without ever trying ALLOC_OOM allocation.
Therefore, this patch allows OOM victims to use ALLOC_OOM watermark
for last second allocation attempt.
[1] http://lkml.kernel.org/r/e6c83a26-1d59-4afd-55cf-04e58bdde188@xxxxxxxxxxxxxxxxxx
Fixes: 696453e66630ad45 ("mm, oom: task_will_free_mem should skip oom_reaped tasks")
Reported-by: Manish Jaggi <mjaggi@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
---
mm/page_alloc.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1607326..45e763e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4111,13 +4111,19 @@ struct page *alloc_pages_before_oomkill(const struct oom_control *oc)
* !__GFP_NORETRY allocation which will never fail due to oom_lock
* already held. And since this allocation attempt does not sleep,
* there is no reason we must use high watermark here.
+ * But anyway, make sure that OOM victims can try ALLOC_OOM watermark
+ * in case they haven't tried ALLOC_OOM watermark.
*/
int alloc_flags = ALLOC_CPUSET | ALLOC_WMARK_HIGH;
gfp_t gfp_mask = oc->gfp_mask | __GFP_HARDWALL;
+ int reserve_flags;
if (!oc->ac)
return NULL;
gfp_mask &= ~__GFP_DIRECT_RECLAIM;
+ reserve_flags = __gfp_pfmemalloc_flags(gfp_mask);
+ if (reserve_flags)
+ alloc_flags = reserve_flags;
return get_page_from_freelist(gfp_mask, oc->order, alloc_flags, oc->ac);
}
--
1.8.3.1
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