zbd: do not lock conventional zones on I/O adjustment

zbd: do not lock conventional zones on I/O adjustment

When a random workload runs against write pointer zones, I/Os are
adjusted to meet write pointer restrictions. During read, I/O offsets
are adjusted to point to zones with data to read and during write, I/O
offsets are adjusted to be at write pointers of open zones.

However, when a random workload runs in a range that contains both
write pointer zones and conventional zones, I/Os to write pointer
zones can potentially be adjusted to conventional zones. The functions
zbd_find_zone() and zbd_convert_to_open_zone() search for zones
regardless of their type, and therefore they may return conventional
zones. These functions lock the found zone to guard its open status
and write pointer position, but this lock is meaningless for
conventional zones. This unwanted lock of conventional zones has been
observed to cause a deadlock.

Furthermore, zbd_convert_to_open_zone() may add the found conventional
zone to the array of open zones. However, conventional zones should
never be added to the array of open zones as conventional zones never
take the "implicit open" condition and not counted as part of the
device open zone management.

To avoid the deadlock, modify zbd_find_zone() not to lock zone when it
checks conventional zone without write pointer. To avoid the deadlock
and the conventional zone open, modify zbd_convert_to_open_zone() to
ignore conventional zones.

Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Dmitry Fomichev <dmitry.fomichev@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>