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

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Date:   Mon, 26 Feb 2018 10:45:11 +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 10:41 AM, Qu Wenruo <quwenruo.btrfs@....com> wrote:
>
>
> On 2018年02月26日 16:33, Amir Goldstein wrote:
>> 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.
>
> Yep, it's definitely needed for a pin-point test case, but I'm also
> wondering if a random, stress test could also help.
>
> Test case with plain fsstress is already super helpful to expose some
> bugs, such stress test won't hurt.
>


Yes, but the same stress test with dm-log-writes instead of dm-flakey
will be as useful and much more, so no reason to merge the less useful
stress test.

Thanks,
Amir.