linux-kernel - Re: xfstests xfs fuzzers fail with DAX

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Date:   Tue, 30 Aug 2016 09:25:45 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     linux-nvdimm <linux-nvdimm@...1.01.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        XFS Developers <xfs@....sgi.com>
Subject: Re: xfstests xfs fuzzers fail with DAX

On Tue, Aug 30, 2016 at 7:53 AM, Dan Williams <dan.j.williams@...el.com> wrote:
> On Mon, Aug 29, 2016 at 7:37 PM, Darrick J. Wong
> <darrick.wong@...cle.com> wrote:
>> On Mon, Aug 29, 2016 at 06:50:05PM -0700, Dan Williams wrote:
>>> [ Adding Darrick on the off chance that this triggers an "aha, of
>>> course it does!" ]
>>
>> Aha!  Of course it does!!! :)
>
> Heh, thanks :).  And apologies to Dave for missing his earlier note
> pointing out the delalloc failure, linux-nvdimm list ate the response.
>
>>
>>> Darrick these corruption tests you added to xfstests last year all
>>> fail the same way with DAX enabled.  They spew:
>>>
>>>     "pwrite64: Structure needs cleaning"
>>>
>>> ...reports that are cleaned up by running without "-o dax".
>>
>> I think this happens because in non-dax mode, the pwrite is a buffered
>> write and so long as we can create a delalloc reservation, everything
>> is ok and nothing fails.  Whereas for dax we have to allocate the
>> blocks for the pwrite immediately, thereby triggering the cntbt
>> verifier error.
>>
>> Proceeding from the assumption "DAX behaves a lot like DIO", all the
>> tests that rely on buffered mode semantics are going to choke if DAX
>> is turned on without them knowing about it.
>>
>>> Alternatively you could sit back and watch me try to figure it out,
>>> that should be quite entertaining... as a start I'll try to pin down a
>>> stack trace when the error is returned.
>>
>> As for how to fix this, probably the best option is to change line 98
>> to 'pwrite -W -S 0x62...' and update the output to include the
>> 'structure needs cleaning' message.
>
> I'll give it a shot.

So, that did not modulate the failure or the passing case.  However,
using -d at line 122 makes the no-dax case fail the same as the dax
case.

Would a change like this be acceptable in the interim while we figure
out which tests are delalloc sensitive, or did I just invalidate the
test?

diff --git a/tests/xfs/086 b/tests/xfs/086
index 143915bafaa1..26607c7a4697 100755
--- a/tests/xfs/086
+++ b/tests/xfs/086
@@ -96,7 +96,7 @@ _scratch_mount

 echo "+ modify files"
 for x in `seq 1 64`; do
-       $XFS_IO_PROG -f -c "pwrite -S 0x62 0 ${blksz}"
"${TESTFILE}.${x}" >> $seqres.full
+       $XFS_IO_PROG -f -c "pwrite -d -S 0x62 0 ${blksz}"
"${TESTFILE}.${x}" >> $seqres.full
 done
 umount "${SCRATCH_MNT}"

@@ -119,7 +119,7 @@ echo "broken: ${broken}"
 # Try appending again, now that we've fixed the fs
 echo "+ modify files (2)"
 for x in `seq 1 64`; do
-       $XFS_IO_PROG -f -c "pwrite -S 0x62 ${blksz} ${blksz}"
"${TESTFILE}.${x}" >> $seqres.fu
+       $XFS_IO_PROG -f -c "pwrite -d -S 0x62 ${blksz} ${blksz}"
"${TESTFILE}.${x}" >> $seqres
 done
 umount "${SCRATCH_MNT}"

diff --git a/tests/xfs/086.out b/tests/xfs/086.out
index 6c053f42deea..e2ec84e6b90f 100644
--- a/tests/xfs/086.out
+++ b/tests/xfs/086.out
@@ -16,5 +16,5 @@ broken: 1
 + mount image
 + chattr -R -i
 + check files (2)
-broken: 0
+broken: 1
 + check fs (2)