On Thu, 14 Aug 2025 13:54:56 +0530, Nilay Shroff wrote:
> This patchset replaces the use of a static key in the I/O path (rq_qos_
> xxx()) with an atomic queue flag (QUEUE_FLAG_QOS_ENABLED). This change
> is made to eliminate a potential deadlock introduced by the use of static
> keys in the blk-rq-qos infrastructure, as reported by lockdep during
> blktests block/005[1].
>
> The original static key approach was introduced to avoid unnecessary
> dereferencing of q->rq_qos when no blk-rq-qos module (e.g., blk-wbt or
> blk-iolatency) is configured. While efficient, enabling a static key at
> runtime requires taking cpu_hotplug_lock and jump_label_mutex, which
> becomes problematic if the queue is already frozen — causing a reverse
> dependency on ->freeze_lock. This results in a lockdep splat indicating
> a potential deadlock.
>
> [...]
Applied, thanks!
[1/3] block: skip q->rq_qos check in rq_qos_done_bio()
commit: 275332877e2fa9d6efa7402b1e897f6c6ee695bb
[2/3] block: decrement block_rq_qos static key in rq_qos_del()
commit: ade1beea1c27657712aa8f594226d461639382ff
[3/3] block: avoid cpu_hotplug_lock depedency on freeze_lock
commit: 370ac285f23aecae40600851fb4a1a9e75e50973
Best regards,
--
Jens Axboe
