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

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Message-ID: <aRW0BmIMpo5Hz_-O@li-dc0c254c-257c-11b2-a85c-98b6c1322444.ibm.com>
Date: Thu, 13 Nov 2025 16:04:33 +0530
From: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: zlang@...hat.com, fstests@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 7/7] generic/774: turn off lfsr

On Mon, Nov 10, 2025 at 10:27:51AM -0800, 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.

Hi Darrick thanks for the fix. Strange that I never observed this but
yes it is not needed.

Feel free to add:
Reviewed-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>

Regards,
ojaswin

> 
> 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>
> ---
>  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
>