From: Ionut Nechita <ionut.nechita@windriver.com>

This series addresses two critical issues in the block layer multiqueue
(blk-mq) subsystem when running on PREEMPT_RT kernels.

The first patch fixes a severe performance regression where queue_lock
contention in the I/O hot path causes IRQ threads to sleep on RT kernels.
Testing on MegaRAID 12GSAS controller showed a 76% performance drop
(640 MB/s -> 153 MB/s). The fix replaces spinlock with memory barriers
to maintain ordering without sleeping.

The second patch fixes a WARN_ON that triggers during SCSI device scanning
when blk_freeze_queue_start() calls blk_mq_run_hw_queues() synchronously
from interrupt context. The warning "WARN_ON_ONCE(!async && in_interrupt())"
is resolved by switching to asynchronous execution.

Changes in v2:
- Removed the blk_mq_cpuhp_lock patch (needs more investigation)
- Added fix for WARN_ON in interrupt context during queue freezing
- Updated commit messages for clarity

Ionut Nechita (2):
  block/blk-mq: fix RT kernel regression with queue_lock in hot path
  block: Fix WARN_ON in blk_mq_run_hw_queue when called from interrupt
    context

 block/blk-mq.c | 21 +++++++++------------
 1 file changed, 9 insertions(+), 12 deletions(-)

-- 
2.52.0