linux-ext4 - Re: [RFC PATCH] fstests: Check if a fs can survive random (emulated) power loss

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Message-ID: <CAOQ4uxhXmoaJbJVCUk-9VXipTxuYhmTHAh89bWZ1xrWUUd76GA@mail.gmail.com>
Date:   Mon, 26 Feb 2018 10:33:17 +0200
From:   Amir Goldstein <amir73il@...il.com>
To:     Qu Wenruo <quwenruo.btrfs@....com>
Cc:     Qu Wenruo <wqu@...e.com>, fstests <fstests@...r.kernel.org>,
        Linux Btrfs <linux-btrfs@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        Ext4 <linux-ext4@...r.kernel.org>,
        Josef Bacik <josef@...icpanda.com>
Subject: Re: [RFC PATCH] fstests: Check if a fs can survive random (emulated)
 power loss

On Mon, Feb 26, 2018 at 10:20 AM, Qu Wenruo <quwenruo.btrfs@....com> wrote:
>
>
> On 2018年02月26日 16:15, Amir Goldstein wrote:
>> On Mon, Feb 26, 2018 at 9:31 AM, Qu Wenruo <wqu@...e.com> wrote:
>>> This test case is originally designed to expose unexpected corruption
>>> for btrfs, where there are several reports about btrfs serious metadata
>>> corruption after power loss.
>>>
>>> The test case itself will trigger heavy fsstress for the fs, and use
>>> dm-flakey to emulate power loss by dropping all later writes.
>>>
>>
>> Come on... dm-flakey is so 2016
>> You should take Josef's fsstress+log-writes test and bring it to fstests:
>> https://github.com/josefbacik/log-writes
>>
>> By doing that you will gain two very important features from the test:
>>
>> 1. Problems will be discovered much faster, because the test can run fsck
>>     after every single block write has been replayed instead of just at random
>>     times like in your test
>
> That's what exactly I want!!!
>
> Great thanks for this one! I would definitely look into this.
> (Although the initial commit is even older than 2016)
>

Please note that Josef's replay-individual-faster.sh script runs fsck
every 1000 writes (i.e. --check 1000), so you can play with this argument
in your test. Can also run --fsck every --check fua or --check flush, which
may be more indicative of real world problems. not sure.

>
> But the test itself could already expose something on EXT4, it still
> makes some sense for ext4 developers as a verification test case.
>

Please take a look at generic/456
When generic/455 found a reproduciable problem in ext4,
I created a specific test without any randomness to pin point the
problem found (using dm-flakey).
If the problem you found is reproduciable, then it will be easy for you
to create a similar "bisected" test.

Thanks,
Amir.