Re: [PATCH] fs: btrfs: extent_map: removed unneeded variable

From: David Sterba
Date: Wed Jun 30 2021 - 06:01:59 EST

On Tue, Jun 29, 2021 at 09:04:40AM +0000, Johannes Thumshirn wrote:
> On 29/06/2021 10:51, lijian_8010a29@xxxxxxx wrote:
> > From: lijian <lijian@xxxxxxxxxx>
> >
> > removed unneeded variable 'ret'.
> Wouldn't it make more sense to return an error (-ENOENT??) in case
> the em lookup fails and handle the error in btrfs_finish_ordered_io()
> as this is the only caller of unpin_extent_cache()?
> I've actually tripped over this a couple of times already when
> investigating extent map and ordered extent splitting problems
> on zoned filesystems:
> em = lookup_extent_mapping(tree, start, len);
> WARN_ON(!em || em->start != start);
> Maybe even turn this WARN_ON() into an ASSERT() when introducing proper
> error handling, as we shouldn't really get there unless we have a logical
> error.

If you have real workloads hitting the warning then it really should be
proper error handling, not even an assert.