linux-ext4 - Re: [PATCH 7/7] generic/774: turn off lfsr

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Message-ID: <20251112181533.GE196366@frogsfrogsfrogs>
Date: Wed, 12 Nov 2025 10:15:33 -0800
From: "Darrick J. Wong" <djwong@...nel.org>
To: John Garry <john.g.garry@...cle.com>
Cc: zlang@...hat.com, fstests@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 7/7] generic/774: turn off lfsr

On Tue, Nov 11, 2025 at 09:01:59AM +0000, John Garry wrote:
> On 10/11/2025 18:27, Darrick J. Wong wrote:
> > From: Darrick J. Wong <djwong@...nel.org>
> > 
> > This test fails mostly-predictably across my testing fleet with:
> > 
> >   --- /run/fstests/bin/tests/generic/774.out	2025-10-20 10:03:43.432910446 -0700
> >   +++ /var/tmp/fstests/generic/774.out.bad	2025-11-10 01:14:58.941775866 -0800
> >   @@ -1,2 +1,11 @@
> >   QA output created by 774
> >   +fio: failed initializing LFSR
> >   +verify: bad magic header 0, wanted acca at file /opt/test-file offset 0, length 33554432 (requested block: offset=0, length=33554432)
> >   +verify: bad magic header 0, wanted acca at file /opt/test-file offset 33554432, length 33554432 (requested block: offset=33554432, length=33554432)
> >   +verify: bad magic header 0, wanted acca at file /opt/test-file offset 67108864, length 33554432 (requested block: offset=67108864, length=33554432)
> >   +verify: bad magic header 0, wanted acca at file /opt/test-file offset 100663296, length 33554432 (requested block: offset=100663296, length=33554432)
> >   +verify: bad magic header 0, wanted acca at file /opt/test-file offset 134217728, length 33554432 (requested block: offset=134217728, length=33554432)
> >   +verify: bad magic header 0, wanted acca at file /opt/test-file offset 167772160, length 33554432 (requested block: offset=167772160, length=33554432)
> >   +verify: bad magic header 0, wanted acca at file /opt/test-file offset 201326592, length 33554432 (requested block: offset=201326592, length=33554432)
> >   +verify: bad magic header 0, wanted acca at file /opt/test-file offset 234881024, length 33554432 (requested block: offset=234881024, length=33554432)
> >   Silence is golden
> > 
> > I'm not sure why the linear feedback shift register algorithm is
> > specifically needed for this test.
> > 
> > Cc: <fstests@...r.kernel.org> # v2025.10.20
> > Fixes: 9117fb93b41c38 ("generic: Add atomic write test using fio verify on file mixed mappings")
> > Signed-off-by: "Darrick J. Wong" <djwong@...nel.org>
> 
> Reviewed-by: John Garry <john.g.garry@...cle.com>
> 
> BTW, if you would like to make further tidy ups, then I don't think that
> verify_write_sequence=0 is required (for verify config). That is only
> relevant when we have multiple threads writing to the same region, which I
> don't think is the case here.

No I would not.  Send a separate patch with a separate justification
please.

--D

> cheers
> 
> > ---
> >   tests/generic/774 |    4 ----
> >   1 file changed, 4 deletions(-)
> > 
> > 
> > diff --git a/tests/generic/774 b/tests/generic/774
> > index 28886ed5b09ff7..86ab01fbd35874 100755
> > --- a/tests/generic/774
> > +++ b/tests/generic/774
> > @@ -56,14 +56,12 @@ group_reporting=1
> >   ioengine=libaio
> >   rw=randwrite
> >   io_size=$((filesize/3))
> > -random_generator=lfsr
> >   # Create unwritten extents
> >   [prep_unwritten_blocks]
> >   ioengine=falloc
> >   rw=randwrite
> >   io_size=$((filesize/3))
> > -random_generator=lfsr
> >   EOF
> >   cat >$fio_aw_config <<EOF
> > @@ -73,7 +71,6 @@ ioengine=libaio
> >   rw=randwrite
> >   direct=1
> >   atomic=1
> > -random_generator=lfsr
> >   group_reporting=1
> >   filename=$testfile
> > @@ -93,7 +90,6 @@ cat >$fio_verify_config <<EOF
> >   [verify_job]
> >   ioengine=libaio
> >   rw=read
> > -random_generator=lfsr
> >   group_reporting=1
> >   filename=$testfile
> > 
> 
>