From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Bart Van Assche To: "osandov@osandov.com" CC: "hare@suse.com" , "linux-block@vger.kernel.org" , "osandov@fb.com" , "axboe@kernel.dk" Subject: Re: [PATCH v4 05/10] blk-mq: Unregister debugfs attributes earlier Date: Mon, 24 Apr 2017 17:24:13 +0000 Message-ID: <1493054652.3394.10.camel@sandisk.com> References: <20170421234026.18970-1-bart.vanassche@sandisk.com> <20170421234026.18970-6-bart.vanassche@sandisk.com> <20170424165549.GC28510@vader.DHCP.thefacebook.com> <1493053923.3394.8.camel@sandisk.com> <20170424171746.GF28510@vader.DHCP.thefacebook.com> In-Reply-To: <20170424171746.GF28510@vader.DHCP.thefacebook.com> Content-Type: text/plain; charset="iso-8859-1" MIME-Version: 1.0 List-ID: On Mon, 2017-04-24 at 10:17 -0700, Omar Sandoval wrote: > On Mon, Apr 24, 2017 at 05:12:05PM +0000, Bart Van Assche wrote: > > On Mon, 2017-04-24 at 09:55 -0700, Omar Sandoval wrote: > > > On Fri, Apr 21, 2017 at 04:40:21PM -0700, Bart Van Assche wrote: > > > > @@ -566,6 +566,11 @@ void blk_cleanup_queue(struct request_queue *q= ) > > > > spin_lock_irq(lock); > > > > if (!q->mq_ops) > > > > __blk_drain_queue(q, true); > > > > + spin_unlock_irq(lock); > > > > + > > > > + blk_mq_debugfs_unregister_mq(q); > > > > + > > > > + spin_lock_irq(lock); > > > > queue_flag_set(QUEUE_FLAG_DEAD, q); > > > > spin_unlock_irq(lock); > > >=20 > > > Do we actually have to hold the queue lock when we set QUEUE_FLAG_DEA= D? > >=20 > > It's way easier to keep that spin_lock()/spin_unlock() pair than to ana= lyze > > the block driver core and all block drivers to see whether or not any > > concurrent queue flag changes could occur. >=20 > Ah, I didn't realize that queue_flag_set() did a non-atomic set. I'm > wondering if anything bad could happen if something raced between when > we drop the lock and regrab it. Maybe just move the > blk_mq_debugfs_unregister_mq() before we grab the lock the first time > instead? That would have the disadvantage that debugfs attributes would be unregiste= red before __blk_drain_queue() is called and hence that these debugfs attribute= s would not be available to debug hangs in queue draining for traditional blo= ck layer queues ... Bart.=