Re: [PATCH v3 2/2] mm/memory-failure: Poison read receives SIGKILL instead of SIGBUS if mmaped more than once

[Naoya Horiguchi]

On Thu, Jul 25, 2019 at 04:01:41PM -0600, Jane Chu wrote:
> Mmap /dev/dax more than once, then read the poison location using address
> from one of the mappings. The other mappings due to not having the page
> mapped in will cause SIGKILLs delivered to the process. SIGKILL succeeds
> over SIGBUS, so user process looses the opportunity to handle the UE.
> 
> Although one may add MAP_POPULATE to mmap(2) to work around the issue,
> MAP_POPULATE makes mapping 128GB of pmem several magnitudes slower, so
> isn't always an option.
> 
> Details -
> 
> ndctl inject-error --block=10 --count=1 namespace6.0
> 
> ./read_poison -x dax6.0 -o 5120 -m 2
> mmaped address 0x7f5bb6600000
> mmaped address 0x7f3cf3600000
> doing local read at address 0x7f3cf3601400
> Killed
> 
> Console messages in instrumented kernel -
> 
> mce: Uncorrected hardware memory error in user-access at edbe201400
> Memory failure: tk->addr = 7f5bb6601000
> Memory failure: address edbe201: call dev_pagemap_mapping_shift
> dev_pagemap_mapping_shift: page edbe201: no PUD
> Memory failure: tk->size_shift == 0
> Memory failure: Unable to find user space address edbe201 in read_poison
> Memory failure: tk->addr = 7f3cf3601000
> Memory failure: address edbe201: call dev_pagemap_mapping_shift
> Memory failure: tk->size_shift = 21
> Memory failure: 0xedbe201: forcibly killing read_poison:22434 because of failure to unmap corrupted page
>   => to deliver SIGKILL
> Memory failure: 0xedbe201: Killing read_poison:22434 due to hardware memory corruption
>   => to deliver SIGBUS
> 
> Signed-off-by: Jane Chu <jane.chu@xxxxxxxxxx>
> Suggested-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>

Thanks for the fix.

Acked-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>