On Mon, May 29, 2023 at 04:59:40PM -0400, Mikulas Patocka wrote:
> Hi
>
> I improved the dm-flakey device mapper target, so that it can do random
> corruption of read and write bios - I uploaded it here:
> https://people.redhat.com/~mpatocka/testcases/bcachefs/dm-flakey.c
>
> I set up dm-flakey, so that it corrupts 10% of read bios and 10% of write
> bios with this command:
> dmsetup create flakey --table "0 `blockdev --getsize /dev/ram0` flakey
> /dev/ram0 0 0 1 4 random_write_corrupt 100000000 random_read_corrupt
> 100000000"
>
>
> I created a bcachefs volume on a single disk (metadata and data checksums
> were turned off) and mounted it on dm-flakey. I got:
>
> crash: https://people.redhat.com/~mpatocka/testcases/bcachefs/crash1.txt
> deadlock: https://people.redhat.com/~mpatocka/testcases/bcachefs/crash2.txt
> infinite loop:
> https://people.redhat.com/~mpatocka/testcases/bcachefs/crash3.txt
>
> Here I uploaded an image that causes infnite loop when we run bcachefs
> fsck on it or when we attempt mount it:
> https://people.redhat.com/~mpatocka/testcases/bcachefs/inf-loop.gz
>
>
> I tried to run bcachefs on two block devices and fuzzing just one of them
> (checksums and replication were turned on - so bcachefs shold correct the
> corrupted data) - in this scenario, bcachefs doesn't return invalid data,
> but it sometimes returns errors and sometimes crashes.
>
> This script will trigger an oops on unmount:
> https://people.redhat.com/~mpatocka/testcases/bcachefs/crash4.txt
> or nonsensical errors returned to userspace:
> rm: cannot remove '/mnt/test/test/cmd_migrate.c': Unknown error 2206
> or I/O errors returned to userspace:
> diff:
> /mnt/test/test/rust-src/target/release/.fingerprint/bch_bindgen-f0bad16858ff0019/lib-bch_bindgen.json:
> Input/output error
>
> #!/bin/sh -ex
> umount /mnt/test || true
> dmsetup remove_all || true
> rmmod brd || true
> SRC=/usr/src/git/bcachefs-tools
> while true; do
> modprobe brd rd_size=1048576
> bcachefs format --replicas=2 /dev/ram0 /dev/ram1
> dmsetup create flakey --table "0 `blockdev --getsize /dev/ram0`
> linear /dev/ram0 0"
> mount -t bcachefs /dev/mapper/flakey:/dev/ram1 /mnt/test
> dmsetup load flakey --table "0 `blockdev --getsize /dev/ram0` flakey
> /dev/ram0 0 0 1 4 random_write_corrupt 100000000 random_read_corrupt
> 100000000"
Hey, that's really neat!
Any chance you'd be willing to get the dm-flakey changes merged into
upstream so that someone can write a recoveryloop fstest to test all the
filesystems systematically?
:D
--D
> dmsetup suspend flakey
> dmsetup resume flakey
> cp -a "$SRC" /mnt/test/test
> diff -r "$SRC" /mnt/test/test
> echo 3 >/proc/sys/vm/drop_caches
> diff -r "$SRC" /mnt/test/test
> echo 3 >/proc/sys/vm/drop_caches
> diff -r "$SRC" /mnt/test/test
> echo 3 >/proc/sys/vm/drop_caches
> rm -rf /mnt/test/test
> echo 3 >/proc/sys/vm/drop_caches
> cp -a "$SRC" /mnt/test/test
> echo 3 >/proc/sys/vm/drop_caches
> diff -r "$SRC" /mnt/test/test
> umount /mnt/test
> dmsetup remove flakey
> rmmod brd
> done
>
> The oops happens in set_btree_iter_dontneed and it is caused by the fact
> that iter->path is NULL. The code in try_alloc_bucket is buggy because it
> sets "struct btree_iter iter = { NULL };" and then jumps to the "err"
> label that tries to dereference values in "iter".
>
>
> Bcachefs gives not much usefull error messages, like "Fatal error: Unknown
> error 2184" or "Error in recovery: cannot allocate memory" or "mount(2)
> system call failed: Unknown error 2186." or "rm: cannot remove
> '/mnt/test/xfstests-dev/tools/fs-walk': Unknown error 2206".
>
> Mikulas
>
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