Re: [PATCH] iomap: Address soft lockup in iomap_finish_ioend()

[Brian Foster <bfoster@redhat.com>]

On Sat, Jan 01, 2022 at 05:39:45PM +0000, Trond Myklebust wrote:
...
> 
> Fair enough. As long as someone is working on a solution, then I'm
> happy. Just a couple of things:
> 
> Firstly, we've verified that the cond_resched() in the bio loop does
> suffice to resolve the issue with XFS, which would tend to confirm what
> you're saying above about the underlying issue being the ioend chain
> length.
> 
> Secondly, note that we've tested this issue with a variety of older
> kernels, including 4.18.x, 5.1.x and 5.15.x, so please bear in mind
> that it would be useful for any fix to be backward portable through the
> stable mechanism.
> 

I've sent a couple or so different variants of this in the past. The
last I believe was here [1], but still never seemed to go anywhere
(despite having reviews on the first couple patches). That one was
essentially a sequence of adding a cond_resched() call in the iomap code
to address the soft lockup warning followed by capping the ioend size
for latency reasons.

Brian

[1] https://lore.kernel.org/linux-xfs/20210517171722.1266878-1-bfoster@redhat.com/

> 
> Thanks, and Happy New Year!
> 
>   Trond
> 
> -- 
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> trond.myklebust@hammerspace.com
> 
>