Re: [PATCH 3/4] btrfs: fix error handling of fallbacked uncompress write

[Naohiro Aota <Naohiro.Aota@wdc.com>]

On Fri, Jun 17, 2022 at 11:21:44AM +0100, Filipe Manana wrote:
> On Fri, Jun 17, 2022 at 12:45:41AM +0900, Naohiro Aota wrote:
> > When cow_file_range() fails in the middle of the allocation loop, it
> > unlocks the pages but remains the ordered extents intact. Thus, we need to
> 
> s/remains/leaves/

Will fix.

> 
> > call btrfs_cleanup_ordered_extents() to finish the created ordered extents.
> > 
> > Also, we need to call end_extent_writepage() if locked_page is available
> > because btrfs_cleanup_ordered_extents() never process the region on the
> > locked_page.
> > 
> > Furthermore, we need to set the mapping as error if locked_page is
> > unavailable before unlocking the pages, so that the errno is properly
> > propagated to the userland.
> > 
> > CC: stable@vger.kernel.org
> 
> It would be better to specify a version here.
>
> The delalloc paths for compression were (a bit heavily) refactored last year
> in preparation for the subpage sector size support, so blindly adding this
> to any stable releases might introduce regressions (assuming the patch does
> not fail to apply).

Yeah ... I could not find the exact commit. It looks like there is no
ordered extent clean up from the beginning.

I'll check if the modified cow_file_range() cause a hang on the stable
versions.

> 
> > Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
> > ---
> >  fs/btrfs/inode.c | 17 +++++++++++++++--
> >  1 file changed, 15 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> > index 4e1100f84a88..cae15924fc99 100644
> > --- a/fs/btrfs/inode.c
> > +++ b/fs/btrfs/inode.c
> > @@ -934,8 +934,18 @@ static int submit_uncompressed_range(struct btrfs_inode *inode,
> >  		goto out;
> >  	}
> >  	if (ret < 0) {
> > -		if (locked_page)
> > +		btrfs_cleanup_ordered_extents(inode, locked_page, start, end - start + 1);
> > +		if (locked_page) {
> > +			u64 page_start = page_offset(locked_page);
> > +			u64 page_end = page_start + PAGE_SIZE - 1;
> > +
> > +			btrfs_page_set_error(inode->root->fs_info, locked_page,
> > +					     page_start, PAGE_SIZE);
> > +			set_page_writeback(locked_page);
> > +			end_page_writeback(locked_page);
> > +			end_extent_writepage(locked_page, ret, page_start, page_end);
> >  			unlock_page(locked_page);
> > +		}
> >  		goto out;
> >  	}
> 
> So as I commented in the previous patch, something is missing here: the call to
> btrfs_cleanup_ordered_extents() at submit_uncompressed_range() in case cow_file_range()
> returns an error.
> 
> Otherwise it looks fine.
> Thanks.

btrfs_cleanup_ordered_extents() is called at the first line of the added
lines. We need to call it regardless of locked_page != NULL or not, because
submit_uncompressed_range() can be called with locked_page = NULL.

> >  
> > @@ -1390,9 +1400,12 @@ static noinline int cow_file_range(struct btrfs_inode *inode,
> >  	 * However, in case of unlock == 0, we still need to unlock the pages
> >  	 * (except @locked_page) to ensure all the pages are unlocked.
> >  	 */
> > -	if (!unlock && orig_start < start)
> > +	if (!unlock && orig_start < start) {
> > +		if (!locked_page)
> > +			mapping_set_error(inode->vfs_inode.i_mapping, ret);
> >  		extent_clear_unlock_delalloc(inode, orig_start, start - 1,
> >  					     locked_page, 0, page_ops);
> > +	}
> >  
> >  	/*
> >  	 * For the range (2). If we reserved an extent for our delalloc range
> > -- 
> > 2.35.1
> >