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

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Message-ID: <PH0PR04MB7416AEA4D23FAE000C86DF729B019@PH0PR04MB7416.namprd04.prod.outlook.com>
Date:   Wed, 30 Jun 2021 11:17:30 +0000
From:   Johannes Thumshirn <Johannes.Thumshirn@....com>
To:     "dsterba@...e.cz" <dsterba@...e.cz>
CC:     "lijian_8010a29@....com" <lijian_8010a29@....com>,
        "clm@...com" <clm@...com>,
        "josef@...icpanda.com" <josef@...icpanda.com>,
        "dsterba@...e.com" <dsterba@...e.com>,
        "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 30/06/2021 12:01, David Sterba wrote:
> On Tue, Jun 29, 2021 at 09:04:40AM +0000, Johannes Thumshirn wrote:
>> 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.
> 
> If you have real workloads hitting the warning then it really should be
> proper error handling, not even an assert.
> 

Up to now it's been coding errors from my side so I think it warrants an
ASSERT().

But still we should handle the error in the caller.