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Re: [BULK] Re: [PATCH] xfstests 311: test fsync with dm flakey V2

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [BULK] Re: [PATCH] xfstests 311: test fsync with dm flakey V2
From: Josef Bacik <jbacik@xxxxxxxxxxxx>
Date: Thu, 25 Apr 2013 20:24:04 -0400
Cc: Josef Bacik <JBacik@xxxxxxxxxxxx>, "linux-btrfs@xxxxxxxxxxxxxxx" <linux-btrfs@xxxxxxxxxxxxxxx>, "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>
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On Thu, Apr 25, 2013 at 04:45:56PM -0600, Dave Chinner wrote:
> On Thu, Apr 25, 2013 at 10:12:56AM -0400, Josef Bacik wrote:
> > This test sets up a dm flakey target and then runs my fsync tester I've been
> > using to verify btrfs's fsync() is working properly.  It will create a dm 
> > flakey
> > device, mount it, run my test, make the flakey device start dropping 
> > writes, and
> > then unmount the fs.  Then we mount it back up and make sure the md5sums 
> > match
> > and then run fsck on the device to make sure we got a consistent fs.  I 
> > used the
> > output from a run on BTRFS since it's the only one that passes this test
> > properly.  I verified each test manually to make sure they were in fact 
> > valid
> > files.  XFS and Ext4 both fail this test in one way or another.  Thanks,
> > 
> > Signed-off-by: Josef Bacik <jbacik@xxxxxxxxxxxx>
> > ---
> > V1->V2
> > -make _test_check_fs take an argument on wether or not to force an exit, 
> > this is
> > because if we failed to fsck we'd leave the dmflakey device around which was
> > super annoying.
> 
> Why doesn't the standard trap command in the test code catch
> the exit case and run the _cleanup function and unmount it?
> 

Yeah I did the trap thing wrong it seems, I will fix that up and back out all of
the related changes, thanks.

> FWIW, if this change is actually necessary, then it needs to be in a
> separate patch.
> 
> > -fixed the drop caches bug (thanks Zach!)
> > -fixed the output since XFS has a bug with that particular test, it leaves 
> > a 0
> > length file behind which isn't right. 
> 
> What test, what bug, and why have you changed the test to work
> around it?
> 

I didn't change the test, I just had to change the golden output.  I was running
it against btrfs and noticed that xfs had different output so I ran the test to
just get the file (no flakey or unmount or anything) and the md5sum matched what
btrfs did and then I looked at the file on xfs and it was empty, so xfs is
messing up one of the testscases.  Sorry I don't remember which one it was, I
was going to run it again and try and track down what was going on tomorrow.

> .....
> > @@ -478,7 +485,7 @@ _scratch_mkfs_ext4()
> >  {
> >     local tmp_dir=/tmp/
> >  
> > -   /sbin/mkfs -t $FSTYP -- $MKFS_OPTIONS $* $SCRATCH_DEV \
> > +   /sbin/mkfs -t $FSTYP -- -F $MKFS_OPTIONS $* $SCRATCH_DEV \
> >                     2>$tmp_dir.mkfserr 1>$tmp_dir.mkfsstd
> >     local mkfs_status=$?
> 
> That seems like an unrelated bug fix?
>

Ergh yeah sorry, I needed this to run the test on ext4, I'll take this out and
send it seperately.

 
> > @@ -1041,6 +1048,27 @@ _require_command()
> >      [ -n "$1" -a -x "$1" ] || _notrun "$_cmd utility required, skipped 
> > this test"
> >  }
> >  
> > +# this test requires the device mapper flakey target
> > +#
> > +_require_dm_flakey()
> > +{
> > +    if [ "$HOSTOS" != "Linux" ]
> > +    then
> > +   _notrun "This test requires linux for dm flakey support"
> > +    fi
> 
> No need to check this - any test that uses dm-flakey should have a
> "_supported_os Linux" line in it.
> 

Ok, just wanted to make sure in case somebody forgot to do the supported os
thing.

> > +    $DMSETUP_PROG targets | grep flakey >/dev/null 2>&1
> > +    if [ $? -eq 0 ]
> > +    then
> > +   :
> > +    else
> > +   _notrun "This test requires dm flakey support"
> > +    fi
> 
> [ $? -ne 0 ] && _notrun "This test requires dm flakey support"
> 
> <snip all the "force exit" mess>
> 
> <snip the fsync-tester.c code>
> 
> FWIW, rebooting the machine at the end of the test should not be the
> default behaviour of fsync-tester.c...
> 

Yeah I can change it to be an option, this is just what I was using originally
to test and I was rebooting the box by default.

> > diff --git a/tests/generic/311 b/tests/generic/311
> > new file mode 100755
> > index 0000000..3f7abe2
> > --- /dev/null
> > +++ b/tests/generic/311
> > @@ -0,0 +1,177 @@
> > +#! /bin/bash
> > +# FS QA Test No. 311
> > +#
> > +#Verify a file systems fsync is working properly.  This won't catch 
> > problems
> > +#with blockdev flushing, but at the very least it makes sure the file 
> > system is
> > +#doing the right thing with fsync logically.
> 
> How is this different to any of the other tests that test fsync() is
> working properly? Please describe what aspect of fsync is being
> tested....
> 
> > +# creator
> > +owner=jbacik@xxxxxxxxxxxx
> 
> We don't need to add these any more.
> 

Ok I'll remove it.

> > +seq=`basename $0`
> > +seqres=$RESULT_DIR/$seq
> > +echo "QA output created by $seq"
> > +
> > +here=`pwd`
> > +status=1   # failure is the default!
> > +
> > +_cleanup()
> > +{
> > +   $UMOUNT_PROG $SCRATCH_MNT > /dev/null 2>&1
> > +   $DMSETUP_PROG remove flakey-test > /dev/null 2>&1
> > +}
> > +
> > +_cleanup
> 
> If we are called with a mounted scratch device, then something has
> gone badly wrong somewhere else - tests *always* start with
> unmounted test and scratch devices.
> 
> What I suspect has gone wrong here is that you've removed the line:
> 
> trap "_cleanup; exit \$status" 0 1 2 3 15
> 
> That will trigger the cleanup function whenever the test exits. I'd
> say this is the cause of the problem you have that has caused you to
> add the "force exit" crap to the filesytsem check functions...
> 

I figured I was doing something stupid, I should have just asked.

> > +# get standard environment, filters and checks
> > +. ./common/rc
> > +. ./common/filter
> > +
> > +# real QA test starts here
> > +_supported_fs generic
> > +_supported_os Linux
> > +_need_to_be_root
> > +_require_scratch
> > +_require_dm_flakey
> > +
> > +[ -x $here/src/fsync-tester ] || _notrun "fsync-tester not build"
> > +
> > +rm -f $seqres.full
> > +BLK_DEV_SIZE=`blockdev --getsz $SCRATCH_DEV`
> > +FLAKEY_DEV=/dev/mapper/flakey-test
> > +SEED=1
> > +testfile=$SCRATCH_MNT/$seq.fsync
> > +
> > +_mount_flakey()
> > +{
> > +   _scratch_options mount
> > +   _mount -t $FSTYP $SCRATCH_OPTIONS $MOUNT_OPTIONS $SELINUX_MOUNT_OPTIONS 
> > $* $FLAKEY_DEV $SCRATCH_MNT
> > +}
> 
> Why do you need to open code all this? We typically don't do
> this for loopback device mounts, so I'm not sure it is necessary
> here. Indeed, if you are testing on the flakey device, you don't
> want XFS using external log or realtime devices, so really just
> something like:
> 
> mount -t $FSTYP $MOUNT_OPTIONS $FLAKEY_DEV $SCRATCH_MNT
> 
> will suffice...

Ok I will do that, I just wanted to be as close to what normal _scratch_mount
does.

> 
> > +_unmount_flakey()
> > +{
> > +   $UMOUNT_PROG $FLAKEY_DEV
> > +}
> 
> Empty line after this needed. FWIW, why use $FLAKEY_DEV here and not
> $SCRATCH_MNT like in the cleanup function?
> 

Just mindlessly copying _umount_scratch()

> 
> > +_drop_writes()
> > +{
> > +   $DMSETUP_PROG suspend flakey-test
> 
> That freezes the filesystem, right?
>
> > +   if [ $? -ne 0 ]; then
> > +           echo "failed to suspend flakey-test"
> > +           _unmount_flakey
> > +           _cleanup
> > +           exit
> > +   fi
> 
> With a properly functioning trap that calls _cleanup(), this can be
> replaced with:
> 
>       [ $? -ne 0 ] && _fatal "failed to suspend flakey-test"
> 
> Same for all the other error cases.
> 
> > +   $DMSETUP_PROG load flakey-test --table "0 $BLK_DEV_SIZE flakey 
> > $SCRATCH_DEV 0 0 180 1 drop_writes"
> 
> Given that there are 2 different table configurations, perhaps
> defining them as variables will make it more obvious. e.g.
> 
> FLAKEY_TABLE="0 $BLK_DEV_SIZE flakey $SCRATCH_DEV 0 0 180 0"
> FLAKEY_WRITE_TABLE="0 $BLK_DEV_SIZE flakey $SCRATCH_DEV 0 0 180 1 drop_writes"
>

Good idea I will do that.
 
> > +_run_test()
> > +{
> > +   test_num=$1
> > +   extra=""
> > +
> > +   [ $2 -eq 1 ] && extra="-d"
> 
> I'm assuming that $2 == 1 means "use direct IO" given it is not
> actually documented? Perhaps "extra" is not such a good name?
>

Yes I was going to add some other stuff but I will just change it to say direct
to make it more obvious.
 
> > +   $here/src/fsync-tester -s $SEED -r -t $test_num $extra $testfile
> > +   if [ $? -ne 0 ]; then
> > +           _unmount_flakey
> > +           _cleanup
> > +           exit
> > +   fi
> > +
> > +   _md5_checksum $testfile
> > +   _drop_writes
> > +   _unmount_flakey
> 
> So, _drop_writes suspends the dm-flakey device, freezes the
> filesystem, turns off writes then thaws the filesystem, right?
>
> If so, doesn't that mean you're not actually testing fsync() as the
> freeze will effectively sync the entire filesystem before you start
> dropping writes?
> 
> I can see why you want to stop unmount from writing back metadata to
> simulate a crash, but if you've already frozen the filesystem then
> writeback has already occurred before you stop the writes. So I
> can't see how this is actually testing fsync - what it appears to be
> testing is the fileystem freeze code...
> 
> [ This is precisely the issue that XFS shutdown ioctls deal with to
> trigger an immediate forced shutdown of the filesystem that prevents
> *any* further writes from being issued by the filesystem - no sync
> operations get in the way and change the state of the filesystem
> after then fsync call, so we know that what is on disk is what was
> written by the sync/fsync calls being tested.
> 
> This is how we test sync/fsync in other XFS tests (e.g.
> xfs/137-140), and this is the reason why us XFS people have
> suggested that other filesystems should implement the ioctls for
> this functionality rather than try to invent new ways of trying
> to stop filesystems from writing back dirty metadata for fsync/sync
> testing....
> 
> Besides, if a corruption is detected, you need a method of stopping
> all dirty metadata from being written back in the filesystem to
> prevent propagation of the corruption.  These ioctls should just be
> an interface into that mechanism. ]
>

So I need to look at what this does.  I don't think it freezes the file system,
because I've run this test and I definitely have a tree log on the file system
after I unmount, which means we didn't actually sync().  Either that or freeze()
is broken for btrfs and it's not actually causing the transaction to commit.  If
it turns out that it is freeze() then it's not actually a fsync tester, but it
seems to still be a valid test since it's definitely causing problems for all
the file systems I've tested and I'll leave this as it is and then write another
real fsync tester.
 
> > +_cleanup
> > +status=0
> > +exit
> 
> No need to call _cleanup if you have a functioning trap. And, more
> importantly, the only reason that status variable exists is so that
> the trap function can ensure a correct exit value from the test.....
> 
> > diff --git a/tests/generic/group b/tests/generic/group
> > index eb52833..a0830c1 100644
> > --- a/tests/generic/group
> > +++ b/tests/generic/group
> > @@ -113,3 +113,4 @@
> >  308 auto quick
> >  309 auto quick
> >  310 auto
> > +311 auto
> 
> How long does this take to run? It seems like the quick group would
> be appropriate if it takes less than a minute. Also, fsync tests
> fall under the category of "metadata" and "log", so they probably
> should be added, too.
> 

It takes 66 seconds to run on btrfs, is that fast enough for quick?  I'll add
metadata and log to the list as well.  Thanks for the thorough review,

Josef

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