linux-kernel - Re: [PATCH] fs: btrfs: extent_map: removed unneeded variable

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Message-ID: <PH0PR04MB741666CF29DB96CF0DB0C26B9B029@PH0PR04MB7416.namprd04.prod.outlook.com>
Date:   Tue, 29 Jun 2021 09:04:40 +0000
From:   Johannes Thumshirn <Johannes.Thumshirn@....com>
To:     "lijian_8010a29@....com" <lijian_8010a29@....com>,
        "clm@...com" <clm@...com>,
        "josef@...icpanda.com" <josef@...icpanda.com>,
        "dsterba@...e.com" <dsterba@...e.com>
CC:     "linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        lijian <lijian@...ong.com>
Subject: Re: [PATCH] fs: btrfs: extent_map: removed unneeded variable

On 29/06/2021 10:51, lijian_8010a29@....com wrote:
> From: lijian <lijian@...ong.com>
> 
> 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.