[PATCH] powerpc/mce: Fix a bug where mce loops on memory UE.

[Balbir Singh]

On Mon, Apr 23, 2018 at 4:51 PM, Balbir Singh <bsingharora at gmail.com> wrote:
> On Mon, Apr 23, 2018 at 2:59 PM, Mahesh J Salgaonkar
> <mahesh at linux.vnet.ibm.com> wrote:
>> From: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
>>
>> The current code extracts the physical address for UE errors and then
>> hooks it up into memory failure infrastructure. On successful extraction
>> of physical address it wrongly sets "handled = 1" which means this UE error
>> has been recovered. Since MCE handler gets return value as handled = 1, it
>> assumes that error has been recovered and goes back to same NIP. This causes
>> MCE interrupt again and again in a loop leading to hard lockup.
>>
>> Also, initialize phys_addr to ULONG_MAX so that we don't end up queuing
>> undesired page to hwpoison.
>>
>> Without this patch we see:
>> [ 1476.541984] Severe Machine check interrupt [Recovered]
>> [ 1476.541985]   NIP: [000000001002588c] PID: 7109 Comm: find
>> [ 1476.541986]   Initiator: CPU
>> [ 1476.541987]   Error type: UE [Load/Store]
>> [ 1476.541988]     Effective address: 00007fffd2755940
>> [ 1476.541989]     Physical address:  000020181a080000
>> [...]
>> [ 1476.542003] Severe Machine check interrupt [Recovered]
>> [ 1476.542004]   NIP: [000000001002588c] PID: 7109 Comm: find
>> [ 1476.542005]   Initiator: CPU
>> [ 1476.542006]   Error type: UE [Load/Store]
>> [ 1476.542006]     Effective address: 00007fffd2755940
>> [ 1476.542007]     Physical address:  000020181a080000
>> [ 1476.542010] Severe Machine check interrupt [Recovered]
>> [ 1476.542012]   NIP: [000000001002588c] PID: 7109 Comm: find
>> [ 1476.542013]   Initiator: CPU
>> [ 1476.542014]   Error type: UE [Load/Store]
>> [ 1476.542015]     Effective address: 00007fffd2755940
>> [ 1476.542016]     Physical address:  000020181a080000
>> [ 1476.542448] Memory failure: 0x20181a08: recovery action for dirty LRU page: Recovered
>> [ 1476.542452] Memory failure: 0x20181a08: already hardware poisoned
>> [ 1476.542453] Memory failure: 0x20181a08: already hardware poisoned
>> [ 1476.542454] Memory failure: 0x20181a08: already hardware poisoned
>> [ 1476.542455] Memory failure: 0x20181a08: already hardware poisoned
>> [ 1476.542456] Memory failure: 0x20181a08: already hardware poisoned
>> [ 1476.542457] Memory failure: 0x20181a08: already hardware poisoned
>> [...]
>> [ 1490.972174] Watchdog CPU:38 Hard LOCKUP
>>
>> After this patch we see:
>>
>> [  325.384336] Severe Machine check interrupt [Not recovered]
>
> How did you test for this? If the error was recovered, shouldn't the
> process have gotten
> a SIGBUS and we should have prevented further access as a part of the handling
> (memory_failure()). Do we just need a MF_MUST_KILL in the flags?
>
> Why shouldn't we treat it as handled if we isolate the page?

Not yet signed-off-by patch attached for testing, Mahesh, please check/confirm

Thanks,
Balbir

>
> Thanks,
> Balbir Singh.
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