On 11/6/20 4:01 AM, Damien Le Moal wrote:
> Commit aa1c09cb65e2 ("null_blk: Fix locking in zoned mode") changed
> zone locking to using the potentially sleeping wait_on_bit_io()
> function. This is acceptable when memory backing is enabled as the
> device queue is in that case marked as blocking, but this triggers a
> scheduling while in atomic context with memory backing disabled.
>
> Fix this by relying solely on the device zone spinlock for zone
> information protection without temporarily releasing this lock around
> null_process_cmd() execution in null_zone_write(). This is OK to do
> since when memory backing is disabled, command processing does not
> block and the memory backing lock nullb->lock is unused. This solution
> avoids the overhead of having to mark a zoned null_blk device queue as
> blocking when memory backing is unused.
>
> This patch also adds comments to the zone locking code to explain the
> unusual locking scheme.
Applied for 5.10, though I do agree that the locking for non-memory
backed should go. The whole point of null_blk is to be able to
benchmark the underlying layers, and if we end up having null_blk
be the limiting factor, then it's pointless.
--
Jens Axboe
