Re: PROBLEM: Recent raid10 block discard patchset causes filesystem corruption on fstrim

From: Xiao Ni <xni@redhat.com>
To: Matthew Ruffell <matthew.ruffell@canonical.com>,
	Song Liu <songliubraving@fb.com>
Cc: linux-raid <linux-raid@vger.kernel.org>,
	Song Liu <song@kernel.org>, lkml <linux-kernel@vger.kernel.org>,
	Coly Li <colyli@suse.de>,
	Guoqing Jiang <guoqing.jiang@cloud.ionos.com>,
	"khalid.elmously@canonical.com" <khalid.elmously@canonical.com>,
	Jay Vosburgh <jay.vosburgh@canonical.com>
Subject: Re: PROBLEM: Recent raid10 block discard patchset causes filesystem corruption on fstrim
Date: Wed, 3 Feb 2021 09:43:33 +0800	[thread overview]
Message-ID: <7fb182e0-a03f-4125-e3db-e9f819e099e4@redhat.com> (raw)
In-Reply-To: <71b9c9df-93a8-165a-d254-746a874f2238@canonical.com>

On 02/02/2021 11:42 AM, Matthew Ruffell wrote:
> Hi Xiao,
>
> On 24/12/20 11:18 pm, Xiao Ni wrote:> The root cause is found. Now we use a similar way with raid0 to handle discard request
>> for raid10. Because the discard region is very big, we can calculate the start/end address
>> for each disk. Then we can submit the discard request to each disk. But for raid10, it has
>> copies. For near layout, if the discard request doesn't align with chunk size, we calculate
>> a start_disk_offset. Now we only use start_disk_offset for the first disk, but it should be
>> used for the near copies disks too.
> Thanks for finding the root cause and making a patch that corrects the offset
> addresses for multiple disks!
>
>> [  789.709501] discard bio start : 70968, size : 191176
>> [  789.709507] first stripe index 69, start disk index 0, start disk offset 70968
>> [  789.709509] last stripe index 256, end disk index 0, end disk offset 262144
>> [  789.709511] disk 0, dev start : 70968, dev end : 262144
>> [  789.709515] disk 1, dev start : 70656, dev end : 262144
>>
>> For example, in this test case, it has 2 near copies. The start_disk_offset for the first disk is 70968.
>> It should use the same offset address for second disk. But it uses the start address of this chunk.
>> It discard more region. The patch in the attachment can fix this problem. It split the region that
>> doesn't align with chunk size.
> Just wondering, what is the current status of the patchset? Is there anything
> that I can do to help?
>
>> There is another problem. The stripe size should be calculated differently for near layout and far layout.
>>
> I can help review the patch and help test the patches anytime. Do you need help
> with making a patch to calculate the stripe size for near and far layouts?
>
> Let me know how you are going with this patchset, and if there is anything I
> can do for you.
>
> Thanks,
> Matthew
>
Hi Matthew

I'm doing the test for the new patch set. I'll send the patch soon 
again. Thanks for the help.

Regards
Xiao