linux-kernel - Re: [RFC PATCH] xfs: drop experimental warning for fsdax

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Message-ID: <20220919211533.GK3600936@dread.disaster.area>
Date:   Tue, 20 Sep 2022 07:15:33 +1000
From:   Dave Chinner <david@...morbit.com>
To:     Shiyang Ruan <ruansy.fnst@...itsu.com>
Cc:     linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        nvdimm@...ts.linux.dev, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, djwong@...nel.org,
        dan.j.williams@...el.com
Subject: Re: [RFC PATCH] xfs: drop experimental warning for fsdax

On Mon, Sep 19, 2022 at 02:50:03PM +1000, Dave Chinner wrote:
> On Thu, Sep 15, 2022 at 09:26:42AM +0000, Shiyang Ruan wrote:
> > Since reflink&fsdax can work together now, the last obstacle has been
> > resolved.  It's time to remove restrictions and drop this warning.
> > 
> > Signed-off-by: Shiyang Ruan <ruansy.fnst@...itsu.com>
> 
> I haven't looked at reflink+DAX for some time, and I haven't tested
> it for even longer. So I'm currently running a v6.0-rc6 kernel with
> "-o dax=always" fstests run with reflink enabled and it's not
> looking very promising.
> 
> All of the fsx tests are failing with data corruption, several
> reflink/clone tests are failing with -EINVAL (e.g. g/16[45]) and
> *lots* of tests are leaving stack traces from WARN() conditions in
> DAx operations such as dax_insert_entry(), dax_disassociate_entry(),
> dax_writeback_mapping_range(), iomap_iter() (called from
> dax_dedupe_file_range_compare()), and so on.
> 
> At thsi point - the tests are still running - I'd guess that there's
> going to be at least 50 test failures by the time it completes -
> in comparison using "-o dax=never" results in just a single test
> failure and a lot more tests actually being run.

The end results with dax+reflink were:

SECTION       -- xfs_dax
=========================

Failures: generic/051 generic/068 generic/074 generic/075
generic/083 generic/091 generic/112 generic/127 generic/164
generic/165 generic/175 generic/231 generic/232 generic/247
generic/269 generic/270 generic/327 generic/340 generic/388
generic/390 generic/413 generic/447 generic/461 generic/471
generic/476 generic/517 generic/519 generic/560 generic/561
generic/605 generic/617 generic/619 generic/630 generic/649
generic/650 generic/656 generic/670 generic/672 xfs/011 xfs/013
xfs/017 xfs/068 xfs/073 xfs/104 xfs/127 xfs/137 xfs/141 xfs/158
xfs/168 xfs/179 xfs/243 xfs/297 xfs/305 xfs/328 xfs/440 xfs/442
xfs/517 xfs/535 xfs/538 xfs/551 xfs/552
Failed 61 of 1071 tests

Ok, so I did a new no-reflink run as a baseline, because it is a
while since I've tested DAX at all:

SECTION       -- xfs_dax_noreflink
=========================
Failures: generic/051 generic/068 generic/074 generic/075
generic/083 generic/112 generic/231 generic/232 generic/269
generic/270 generic/340 generic/388 generic/461 generic/471
generic/476 generic/519 generic/560 generic/561 generic/617
generic/650 generic/656 xfs/011 xfs/013 xfs/017 xfs/073 xfs/297
xfs/305 xfs/517 xfs/538
Failed 29 of 1071 tests

Yeah, there's still lots of warnings from dax_insert_entry() and
friends like:

[43262.025815] WARNING: CPU: 9 PID: 1309428 at fs/dax.c:380 dax_insert_entry+0x2ab/0x320
[43262.028355] Modules linked in:
[43262.029386] CPU: 9 PID: 1309428 Comm: fsstress Tainted: G W          6.0.0-rc6-dgc+ #1543
[43262.032168] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
[43262.034840] RIP: 0010:dax_insert_entry+0x2ab/0x320
[43262.036358] Code: 08 48 83 c4 30 5b 5d 41 5c 41 5d 41 5e 41 5f c3 48 8b 58 20 48 8d 53 01 e9 65 ff ff ff 48 8b 58 20 48 8d 53 01 e9 50 ff ff ff <0f> 0b e9 70 ff ff ff 31 f6 4c 89 e7 e8 84 b1 5a 00 eb a4 48 81 e6
[43262.042255] RSP: 0018:ffffc9000a0cbb78 EFLAGS: 00010002
[43262.043946] RAX: ffffea0018cd1fc0 RBX: 0000000000000001 RCX: 0000000000000001
[43262.046233] RDX: ffffea0000000000 RSI: 0000000000000221 RDI: ffffea0018cd2000
[43262.048518] RBP: 0000000000000011 R08: 0000000000000000 R09: 0000000000000000
[43262.050762] R10: ffff888241a6d318 R11: 0000000000000001 R12: ffffc9000a0cbc58
[43262.053020] R13: ffff888241a6d318 R14: ffffc9000a0cbe20 R15: 0000000000000000
[43262.055309] FS:  00007f8ce25e2b80(0000) GS:ffff8885fec80000(0000) knlGS:0000000000000000
[43262.057859] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[43262.059713] CR2: 00007f8ce25e1000 CR3: 0000000152141001 CR4: 0000000000060ee0
[43262.061993] Call Trace:
[43262.062836]  <TASK>
[43262.063557]  dax_fault_iter+0x243/0x600
[43262.064802]  dax_iomap_pte_fault+0x199/0x360
[43262.066197]  __xfs_filemap_fault+0x1e3/0x2c0
[43262.067602]  __do_fault+0x31/0x1d0
[43262.068719]  __handle_mm_fault+0xd6d/0x1650
[43262.070083]  ? do_mmap+0x348/0x540
[43262.071200]  handle_mm_fault+0x7a/0x1d0
[43262.072449]  ? __kvm_handle_async_pf+0x12/0xb0
[43262.073908]  exc_page_fault+0x1d9/0x810
[43262.075123]  asm_exc_page_fault+0x22/0x30
[43262.076413] RIP: 0033:0x7f8ce268bc23

So it looks to me like DAX is well and truly broken in 6.0-rc6. And,
yes, I'm running the fixes in mm-hotifxes-stable branch that allow
xfs/550 to pass.

Who is actually testing this DAX code, and what are they actually
testing on? These are not random failures - I haven't run DAX
testing since ~5.18, and none of these failures were present on the
same DAX test VM running the same configuration back then....

-Dave.
-- 
Dave Chinner
david@...morbit.com