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" 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
