Subject: Re: blk_mq_sched_insert_request: inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage

From: Bart Van Assche <[email-masked]>
Date: Fri, 28 Jul 2017 15:13:44 +0000

On Fri, 2017-07-28 at 08:25 -0600, Jens Axboe wrote:
> On 07/28/2017 12:19 AM, Michael Ellerman wrote:
> > OK, so the resolution is "fix it in IPR" ?
> 
> I'll leave that to the SCSI crew. But at least one bug is in IPR, if you
> look at the call trace:
> 
> - timer function triggers, runs ipr_reset_timer_done(), which grabs the
>   host lock AND disables interrupts.
> - further down in the call path, ipr_ioa_bringdown_done() uncondtionally
>   enables interrupts:
> 
>                 spin_unlock_irq(ioa_cfg->host->host_lock);
>                 scsi_unblock_requests(ioa_cfg->host);
>                 spin_lock_irq(ioa_cfg->host->host_lock); 
> 
> And the call to scsi_unblock_requests() is the one that ultimately runs
> the queue. The IRQ issue aside here, scsi_unblock_requests() could run
> the queue async, and we could retain the normal sync run otherwise.
> 
> Can you try the below fix? Should be more palatable than the previous
> one. Brian, maybe you can take a look at the IRQ issue mentioned above?
> 
> [ ... ]

Hello Jens,

Are there other block drivers that can call blk_mq_start_hw_queues() from
interrupt context? I'm currently working on converting the skd driver
(drivers/block/skd_main.c) from a single queue block driver into a scsi-mq
driver. The skd driver calls blk_start_queue() from interrupt context. As we
know it is not safe to call blk_mq_start_hw_queues() from interrupt context.
Can you recommend me how I should proceed: should I implement a solution in
the skd driver or should perhaps the blk-mq core be modified?

Thanks,

Bart.