[dm-devel] dm bufio: fix deadlock issue with loop device

[Junxiao Bi]

On 7/8/19 7:14 AM, Mike Snitzer wrote:

> On Fri, Jul 05 2019 at  4:24pm -0400,
> Junxiao Bi <junxiao.bi at oracle.com> wrote:
>
>> Hi Mike,
>>
>> Do i make sense on this?
> No, you haven't made your chase for this change.  Sorry.
>
> Please refine the patch header to _not_ get into context you have from
> a vendor kernel.  I know you say this is hard to reproduce, etc.
Thanks, I will refine it in v2.
> But
> you don't even get into ther usecase where the issue was seen.  Was this
> DM thinp?  DM cache?  Something else?
it's thin-provision target. Customer is using docker.
>
> Please be as concise and precise as possible.  Saying that shrinker is
> the same context as loop doesn't imply a whole lot to me (relative to
> why this is prone to deadlock).
>
> To restate my concern: if __GFP_FS isn't set then why does your patch
> help at all?  If __GFP_FS is set, then that changes things..

If __GFP_FS isn't set, the behavior is the same with w/o this patch. If 
it is set and the mutex was already hold by others, shrinker stop, 
deadlock avoid.

Thanks,

Junxiao.

>
> Mike