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

From: Matthew Ruffell <matthew.ruffell@canonical.com>
To: Xiao Ni <xni@redhat.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: Tue, 2 Feb 2021 16:42:20 +1300	[thread overview]
Message-ID: <71b9c9df-93a8-165a-d254-746a874f2238@canonical.com> (raw)
In-Reply-To: <a85943ed-60d4-05ad-9f6d-d76324fa5538@redhat.com>

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

> @Song, do you want me to use a separate patch for this fix, or fix this in the original patch?
> 
> Merry Christmas
> Xiao
> 