Re: [PATCH] btrfs: btrfs_wait_tree_block_writeback can be void return

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On Fri, May 26, 2017 at 12:49:25PM -0700, Liu Bo wrote:
> On Fri, May 26, 2017 at 07:08:31PM +0200, David Sterba wrote:
> > On Thu, May 25, 2017 at 06:39:52AM -0400, Jeff Layton wrote:
> > > Nothing checks its return value.
> > 
> > I think we don't need to check the return value of
> > filemap_fdatawait_range, because the errors are tracked by other means
> > (attached to the btree_inode mapping that represents the metadata), in
> > set_btree_ioerr.
> > 
> > > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> > > Reviewed-by: Jan Kara <jack@xxxxxxx>
> > > Reviewed-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
> > 
> > To Liu Bo:
> > 
> > May I ask if you did a review that matches the above understanding? It's
> > trivial to see that nothing really checks the return value of
> > btrfs_wait_tree_block_writeback but my question is if it's really safe
> > not to so. Thanks.
> 
> About the question if it's safe not to do so, I think yes, it's used in
> walk_log_tree which is called in two places, free_log_tree and log replay.  For
> free_log_tree, it waits for any running writeback of the extent buffer under
> freeing to finish in case we need to access the eb pointer from page->private,
> and it's OK to not check the return value, while for log replay, it's doesn't
> wait because wc->wait is not set. So neither cares about the writeback error.

Thanks, I'll update the changelog.
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