Odd SIGSEGV issue introduced by commit 6b31d5955cb29 ("mm, oom: fix potential data corruption when oom_reaper races with writer")

[Christophe LEROY]

Le 20/08/2018 à 18:01, Michal Hocko a écrit :
> On Mon 20-08-18 17:23:58, Christophe LEROY wrote:
>> Hello,
>>
>> I have an odd issue on my powerpc 8xx board.
>>
>> I am running latest 4.14 and get the following SIGSEGV which appears more or
>> less randomly.
>>
>> [    9.190354] touch[91]: unhandled signal 11 at 67807b58 nip 777cf114 lr
>> 777cf100 code 30001
>> [   24.634810] ifconfig[160]: unhandled signal 11 at 67ae7b58 nip 77aaf114
>> lr 77aaf100 code 30001
>> [   30.383737] default.deconfi[231]: unhandled signal 11 at 67c8bb58 nip
>> 77c53114 lr 77c53100 code 30001
>> [   37.655588] S15syslogd[251]: unhandled signal 11 at 6784fb58 nip 77817114
>> lr 77817100 code 30001
>> [   40.974649] snmpd[315]: unhandled signal 11 at 67e0bb58 nip 77dd3114 lr
>> 77dd3100 code 30001
>> [   43.220964] exe[338]: unhandled signal 11 at 67cd3b58 nip 77c9b114 lr
>> 77c9b100 code 30001
>> [   44.191494] exe[348]: unhandled signal 11 at 67c1fb58 nip 77be7114 lr
>> 77be7100 code 30001
>> [   59.175022] sleep[655]: unhandled signal 11 at 67ca3b58 nip 77c6b114 lr
>> 77c6b100 code 30001
>> [   61.853406] smcroute[705]: unhandled signal 11 at 6789bb58 nip 77863114
>> lr 77863100 code 30001
>> [   64.662431] smcroute[778]: unhandled signal 11 at 67e03b58 nip 77dcb114
>> lr 77dcb100 code 30001
>> [   65.623103] smcroute[795]: unhandled signal 11 at 67bdbb58 nip 77ba3114
>> lr 77ba3100 code 30001
>> [   66.579416] exe[825]: unhandled signal 11 at 67edbb58 nip 77ea3114 lr
>> 77ea3100 code 30001
>> [   68.382941] exe[864]: unhandled signal 11 at 6789bb58 nip 77863114 lr
>> 77863100 code 30001
>> [   95.187346] exe[1147]: unhandled signal 11 at 67e83b58 nip 77e4b114 lr
>> 77e4b100 code 30001
>> [  105.238218] exe[1158]: unhandled signal 11 at 67ca3b58 nip 77c6b114 lr
>> 77c6b100 code 30001
>> [  127.556731] exe[1181]: unhandled signal 11 at 67cc3b58 nip 77c8b114 lr
>> 77c8b100 code 30001
>> [  135.558982] exe[1195]: unhandled signal 11 at 678d7b58 nip 7789f114 lr
>> 7789f100 code 30001
>> [  147.579142] exe[1216]: unhandled signal 11 at 67c6bb58 nip 77c33114 lr
>> 77c33100 code 30001
>> [  175.538747] exe[1262]: unhandled signal 11 at 67e2fb58 nip 77df7114 lr
>> 77df7100 code 30001
>> [  186.552670] exe[1275]: unhandled signal 11 at 6781fb58 nip 777e7114 lr
>> 777e7100 code 30001
>> [  230.629786] exe[1344]: unhandled signal 11 at 67cb3b58 nip 77c7b114 lr
>> 77c7b100 code 30001
>> [  249.640396] repair-service.[1369]: unhandled signal 11 at 67e5fb58 nip
>> 77e27114 lr 77e27100 code 30001
>> [  378.003410] exe[1593]: unhandled signal 11 at 678d7b58 nip 7789f114 lr
>> 7789f100 code 30001
>> [  414.060661] exe[1656]: unhandled signal 11 at 67cc7b58 nip 77c8f114 lr
>> 77c8f100 code 30001
>>
>> The problem is present in 3.13, 3.14 and 3.15.
>>
>> I bisected its appearance with commit 6b31d5955cb29 ("mm, oom: fix potential
>> data corruption when oom_reaper races with writer")
> 
> Do you see any oom killer invocations preceeding the SEGV? Some of those
> killed tasks simply do not look like a sensible oom victims (e.g.
> touch)...

No I don't see any.

> 
>> And I bisected its disappearance with commit 99cd1302327a2 ("powerpc:
>> Deliver SEGV signal on pkey violation")
> 
> Those two seem completely unrelated.
> 

That's my feeling too, hence my incredulity