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

Dave Chinner
2022-04-03T23:28:30Z

On Thu, Mar 31, 2022 at 06:24:20PM +0530, Ritesh Harjani wrote:
> From: Ritesh Harjani <riteshh@linux.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@linux.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@fromorbit.com