On Tue, Jun 21, 2022 at 09:39:19AM +0200, Sebastian Andrzej Siewior wrote: > __blk_mq_delay_run_hw_queue() disables preemption to get a stable > current CPU number and then invokes __blk_mq_run_hw_queue() if the CPU > number is part the mask. > > __blk_mq_run_hw_queue() acquires a spin_lock_t which is a sleeping lock > on PREEMPT_RT and can't be acquired with disabled preemption. > > If it is important that the current CPU matches the requested CPU mask > and that the context does not migrate to another CPU while > __blk_mq_run_hw_queue() is invoked then it possible to achieve this by > disabling migration and keeping the context preemptible. > > Disable only migration while testing the CPU mask and invoking > __blk_mq_run_hw_queue(). > > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> > Link: https://lore.kernel.org/r/YnQHqx/5+54jd+U+@xxxxxxxxxxxxx > Link: https://lore.kernel.org/r/YqISXf6GAQeWqcR+@xxxxxxxxxxxxx > --- > block/blk-mq.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -2083,14 +2083,14 @@ static void __blk_mq_delay_run_hw_queue( > return; > > if (!async && !(hctx->flags & BLK_MQ_F_BLOCKING)) { > - int cpu = get_cpu(); > - if (cpumask_test_cpu(cpu, hctx->cpumask)) { > + migrate_disable(); > + if (cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask)) { > __blk_mq_run_hw_queue(hctx); > - put_cpu(); > + migrate_enable(); I think you can replace it with raw_smp_processor_id() directly without disabling migration. Both async run queue and direct issue can run on cpu not on hctx->cpumask, so it is fine for sync run queue too. Thanks, Ming
