linux-ext4 - Re: [PATCHv3 1/4] generic/468: Add another falloc test entry

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Message-ID: <20220403232823.GS1609613@dread.disaster.area>
Date:   Mon, 4 Apr 2022 09:28:23 +1000
From:   Dave Chinner <david@...morbit.com>
To:     Ritesh Harjani <ritesh.list@...il.com>
Cc:     fstests <fstests@...r.kernel.org>, linux-ext4@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        "Darrick J . Wong" <djwong@...nel.org>,
        Ritesh Harjani <riteshh@...ux.ibm.com>
Subject: Re: [PATCHv3 1/4] generic/468: Add another falloc test entry

On Thu, Mar 31, 2022 at 06:24:20PM +0530, Ritesh Harjani wrote:
> From: Ritesh Harjani <riteshh@...ux.ibm.com>
> 
> Add another falloc test entry which could hit a kernel bug
> with ext4 fast_commit feature w/o below kernel commit [1].
> 
> <log>
> [  410.888496][ T2743] BUG: KASAN: use-after-free in ext4_mb_mark_bb+0x26a/0x6c0
> [  410.890432][ T2743] Read of size 8 at addr ffff888171886000 by task mount/2743
> 
> This happens when falloc -k size is huge which spans across more than
> 1 flex block group in ext4. This causes a bug in fast_commit replay
> code which is fixed by kernel commit at [1].
> 
> [1]: https://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git/commit/?h=dev&id=bfdc502a4a4c058bf4cbb1df0c297761d528f54d
> 
> Signed-off-by: Ritesh Harjani <riteshh@...ux.ibm.com>
> ---
>  tests/generic/468     | 8 ++++++++
>  tests/generic/468.out | 2 ++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/tests/generic/468 b/tests/generic/468
> index 95752d3b..5e73cff9 100755
> --- a/tests/generic/468
> +++ b/tests/generic/468
> @@ -34,6 +34,13 @@ _scratch_mkfs >/dev/null 2>&1
>  _require_metadata_journaling $SCRATCH_DEV
>  _scratch_mount
>  
> +# blocksize and fact are used in the last case of the fsync/fdatasync test.
> +# This is mainly trying to test recovery operation in case where the data
> +# blocks written, exceeds the default flex group size (32768*4096*16) in ext4.
> +blocks=32768
> +blocksize=4096

Block size can change based on mkfs parameters. You should extract
this dynamically from the filesystem the test is being run on.

> +fact=18

What is "fact" supposed to mean?

Indeed, wouldn't this simply be better as something like:

larger_than_ext4_fg_size=$((32768 * $blksize * 18))

And then

>  testfile=$SCRATCH_MNT/testfile
>  
>  # check inode metadata after shutdown
> @@ -85,6 +92,7 @@ for i in fsync fdatasync; do
>  	test_falloc $i "-k " 1024
>  	test_falloc $i "-k " 4096
>  	test_falloc $i "-k " 104857600
> +	test_falloc $i "-k " $(($blocks*$blocksize*$fact))

	test_falloc $i "-k " $larger_than_ext4_fg_size

And just scrub all the sizes from the golden output?

Cheers,

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