Raid456 module had allowed to achieve failed state. It was fixed by
fb73b357 ("raid5: block failing device if raid will be failed").
This fix introduces a bug, now if raid5 fails during IO, it may result
with a hung task without completion. Faulty flag on the device is
necessary to process all requests and is checked many times, mainly in
analyze_stripe().
Allow to set faulty on drive again and set MD_BROKEN if raid is failed.

As a result, this level is allowed to achieve failed state again, but
communication with userspace (via -EBUSY status) will be preserved.

This restores possibility to fail array via #mdadm --set-faulty command
and will be fixed by additional verification on mdadm side.

Reproduction steps:
 mdadm -CR imsm -e imsm -n 3 /dev/nvme[0-2]n1
 mdadm -CR r5 -e imsm -l5 -n3 /dev/nvme[0-2]n1 --assume-clean
 mkfs.xfs /dev/md126 -f
 mount /dev/md126 /mnt/root/

 fio --filename=/mnt/root/file --size=5GB --direct=1 --rw=randrw
--bs=64k --ioengine=libaio --iodepth=64 --runtime=240 --numjobs=4
--time_based --group_reporting --name=throughput-test-job
--eta-newline=1 &

 echo 1 > /sys/block/nvme2n1/device/device/remove
 echo 1 > /sys/block/nvme1n1/device/device/remove

 [ 1475.787779] Call Trace:
 [ 1475.793111] __schedule+0x2a6/0x700
 [ 1475.799460] schedule+0x38/0xa0
 [ 1475.805454] raid5_get_active_stripe+0x469/0x5f0 [raid456]
 [ 1475.813856] ? finish_wait+0x80/0x80
 [ 1475.820332] raid5_make_request+0x180/0xb40 [raid456]
 [ 1475.828281] ? finish_wait+0x80/0x80
 [ 1475.834727] ? finish_wait+0x80/0x80
 [ 1475.841127] ? finish_wait+0x80/0x80
 [ 1475.847480] md_handle_request+0x119/0x190
 [ 1475.854390] md_make_request+0x8a/0x190
 [ 1475.861041] generic_make_request+0xcf/0x310
 [ 1475.868145] submit_bio+0x3c/0x160
 [ 1475.874355] iomap_dio_submit_bio.isra.20+0x51/0x60
 [ 1475.882070] iomap_dio_bio_actor+0x175/0x390
 [ 1475.889149] iomap_apply+0xff/0x310
 [ 1475.895447] ? iomap_dio_bio_actor+0x390/0x390
 [ 1475.902736] ? iomap_dio_bio_actor+0x390/0x390
 [ 1475.909974] iomap_dio_rw+0x2f2/0x490
 [ 1475.916415] ? iomap_dio_bio_actor+0x390/0x390
 [ 1475.923680] ? atime_needs_update+0x77/0xe0
 [ 1475.930674] ? xfs_file_dio_aio_read+0x6b/0xe0 [xfs]
 [ 1475.938455] xfs_file_dio_aio_read+0x6b/0xe0 [xfs]
 [ 1475.946084] xfs_file_read_iter+0xba/0xd0 [xfs]
 [ 1475.953403] aio_read+0xd5/0x180
 [ 1475.959395] ? _cond_resched+0x15/0x30
 [ 1475.965907] io_submit_one+0x20b/0x3c0
 [ 1475.972398] __x64_sys_io_submit+0xa2/0x180
 [ 1475.979335] ? do_io_getevents+0x7c/0xc0
 [ 1475.986009] do_syscall_64+0x5b/0x1a0
 [ 1475.992419] entry_SYSCALL_64_after_hwframe+0x65/0xca
 [ 1476.000255] RIP: 0033:0x7f11fc27978d
 [ 1476.006631] Code: Bad RIP value.
 [ 1476.073251] INFO: task fio:3877 blocked for more than 120 seconds.

Cc: stable@vger.kernel.org
Fixes: fb73b357 ("raid5: block failing device if raid will be failed")
Reviewd-by: Xiao Ni <xni@redhat.com>
Signed-off-by: Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>
Signed-off-by: Song Liu <song@kernel.org>