From: Bart Van Assche <bvanassche@acm.org>
To: dgilbert@interlog.com, Christoph Hellwig <hch@infradead.org>
Cc: SCSI development list <linux-scsi@vger.kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
James Bottomley <james.bottomley@hansenpartnership.com>,
Milan Broz <gmazyland@gmail.com>
Subject: Re: [PATCH] scsi_debug: deadlock between completions and surprise module removal
Date: Fri, 05 Sep 2014 17:25:04 +0200 [thread overview]
Message-ID: <5409D5D0.8060801@acm.org> (raw)
In-Reply-To: <5409C116.5060702@interlog.com>
On 09/05/14 15:56, Douglas Gilbert wrote:
> With scsi-mq I think many LLDs probably have a new
> race possibility between a surprise rmmod of the LLD
> and another thread presenting a new command at about
> the same time (or another thread's command completing
> around that time). Does anything above the LLD stop
> this happening?
>
> Looking at mpt3sas and hpsa module exit calls, they don't
> seem to guard against this possibility.
>
> The test is pretty easy: build the LLD as a module, load
> it and fire up a multi-thread, libaio fio test on one or
> more devices (SSDs would probably be good) on that LLD.
> While the test is running, do 'rmmod LLD'.
An LLD must call scsi_remove_host() directly or indirectly from the
module cleanup path. scsi_remove_host() triggers a call to
blk_cleanup_queue(). That last function sets the flag QUEUE_FLAG_DYING
which prevents that new I/O is queued and waits until previously queued
requests have finished before returning.
Bart.
next prev parent reply other threads:[~2014-09-05 15:25 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-31 23:09 [PATCH] scsi_debug: deadlock between completions and surprise module removal Douglas Gilbert
2014-09-01 15:36 ` Christoph Hellwig
2014-09-01 19:52 ` Douglas Gilbert
2014-09-05 5:24 ` Christoph Hellwig
2014-09-05 13:56 ` Douglas Gilbert
2014-09-05 15:25 ` Bart Van Assche [this message]
2014-09-06 14:40 ` Douglas Gilbert
2014-09-06 14:44 ` Christoph Hellwig
2014-09-08 9:11 ` Bart Van Assche
2014-09-08 15:07 ` Christoph Hellwig
2014-09-08 20:31 ` Douglas Gilbert
2014-09-09 15:30 ` Christoph Hellwig
2014-09-25 12:13 ` Christoph Hellwig
2014-10-03 18:16 ` Elliott, Robert (Server Storage)
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