From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: linux-block@vger.kernel.org
Cc: Christoph Hellwig <hch@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
David Runge <dave@sleepmap.de>,
linux-rt-users@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Daniel Wagner <dwagner@suse.de>, Mike Galbraith <efault@gmx.de>
Subject: Re: [PATCH 3/3] blk-mq: Use llist_head for blk_cpu_done
Date: Thu, 29 Oct 2020 14:12:12 +0100 [thread overview]
Message-ID: <20201029131212.dsulzvsb6pahahbs@linutronix.de> (raw)
In-Reply-To: <20201028141251.3608598-3-bigeasy@linutronix.de>
On 2020-10-28 15:12:51 [+0100], To linux-block@vger.kernel.org wrote:
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -667,14 +632,21 @@ bool blk_mq_complete_request_remote(struct request *rq)
> return false;
>
> if (blk_mq_complete_need_ipi(rq)) {
…
> } else {
> if (rq->q->nr_hw_queues > 1)
> return false;
> - blk_mq_trigger_softirq(rq);
> + cpu_list = this_cpu_ptr(&blk_cpu_done);
> + if (llist_add(&rq->ipi_list, cpu_list))
> + raise_softirq(BLOCK_SOFTIRQ);
> }
>
> return true;
So Mike posted this:
| BUG: using smp_processor_id() in preemptible [00000000] code: usb-storage/841
| caller is blk_mq_complete_request_remote.part.0+0xa2/0x120
| CPU: 0 PID: 841 Comm: usb-storage Not tainted 5.10.0-rc1+ #61
| Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-1 04/01/2014
| Call Trace:
| dump_stack+0x77/0x97
| check_preemption_disabled+0xbe/0xc0
| blk_mq_complete_request_remote.part.0+0xa2/0x120
| blk_mq_complete_request+0x2e/0x40
| usb_stor_control_thread+0x29a/0x300
| kthread+0x14b/0x170
| ret_from_fork+0x22/0x30
This comes from this_cpu_ptr() because usb_stor_control_thread() runs
with enabled preemption.
Adding preempt_disable() around it will make the warning go away but
will wake the ksoftirqd (this happens now, too).
Adding local_bh_disable() around it would perform the completion
immediately (instead of waking kssoftirqd) but local_bh_enable() feels
slightly more expensive.
Are there many drivers completing the SCSI requests in preemtible
context? In this case it would be more efficient to complete the request
directly (usb_stor_control_thread() goes to sleep after that anyway and
there is only one request at a time).
Sebastian
next prev parent reply other threads:[~2020-10-29 13:12 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-21 17:50 5.9.1-rt18: issues with Firewire card on AMD hardware David Runge
2020-10-23 11:04 ` [PATCH RFC] blk-mq: Don't IPI requests on PREEMPT_RT Sebastian Andrzej Siewior
2020-10-23 11:21 ` Christoph Hellwig
2020-10-23 13:52 ` Sebastian Andrzej Siewior
2020-10-27 9:26 ` Christoph Hellwig
2020-10-27 10:11 ` Sebastian Andrzej Siewior
2020-10-27 16:07 ` Christoph Hellwig
2020-10-27 17:05 ` Thomas Gleixner
2020-10-27 17:23 ` Christoph Hellwig
2020-10-27 17:59 ` Sebastian Andrzej Siewior
2020-10-27 20:58 ` Sebastian Andrzej Siewior
2020-10-28 6:56 ` Christoph Hellwig
2020-10-28 14:12 ` [PATCH 1/3] blk-mq: Don't complete on a remote CPU in force threaded mode Sebastian Andrzej Siewior
2020-10-28 14:12 ` [PATCH 2/3] blk-mq: Always complete remote completions requests in softirq Sebastian Andrzej Siewior
2020-10-28 14:12 ` [PATCH 3/3] blk-mq: Use llist_head for blk_cpu_done Sebastian Andrzej Siewior
2020-10-28 14:44 ` Christoph Hellwig
2020-10-28 14:47 ` Sebastian Andrzej Siewior
2020-10-29 13:12 ` Sebastian Andrzej Siewior [this message]
2020-10-29 14:05 ` Christoph Hellwig
2020-10-29 14:56 ` Sebastian Andrzej Siewior
2020-10-29 14:57 ` Christoph Hellwig
2020-10-29 20:03 ` Sagi Grimberg
2020-10-29 21:01 ` Sebastian Andrzej Siewior
2020-10-29 21:07 ` Sagi Grimberg
2020-10-31 10:41 ` Sebastian Andrzej Siewior
2020-10-31 15:00 ` Jens Axboe
2020-10-31 15:01 ` Jens Axboe
2020-10-31 18:09 ` Christoph Hellwig
2020-11-02 9:55 ` Sebastian Andrzej Siewior
2020-11-02 18:12 ` Christoph Hellwig
2020-11-04 19:15 ` Sagi Grimberg
2020-11-06 15:23 ` Sebastian Andrzej Siewior
2020-10-28 10:04 ` [PATCH RFC] blk-mq: Don't IPI requests on PREEMPT_RT Peter Zijlstra
2020-10-26 0:37 ` 5.9.1-rt18: issues with Firewire card on AMD hardware David Runge
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