From: Tejun Heo <tj@kernel.org>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: axboe@kernel.dk, jgarzik@pobox.com, davem@davemloft.net,
hch@infradead.org, ctalbott@google.com, rni@google.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/6] block: add blk_queue_dead()
Date: Wed, 26 Oct 2011 12:25:48 -0700 [thread overview]
Message-ID: <20111026192548.GB24261@google.com> (raw)
In-Reply-To: <20111026172049.GD355@redhat.com>
Hello,
On Wed, Oct 26, 2011 at 01:20:49PM -0400, Vivek Goyal wrote:
> On Tue, Oct 25, 2011 at 06:02:05PM -0700, Tejun Heo wrote:
> > @@ -603,7 +603,7 @@ EXPORT_SYMBOL(blk_init_allocated_queue_node);
> >
> > int blk_get_queue(struct request_queue *q)
> > {
> > - if (likely(!test_bit(QUEUE_FLAG_DEAD, &q->queue_flags))) {
> > + if (likely(!blk_queue_dead(q))) {
> > kobject_get(&q->kobj);
> > return 0;
>
> I thought DEAD flag is now synchronized with queue lock. So the protocol
> is that caller should be holding queue lock here first?
The requirement is that issue and processing of requests don't happen
once DEAD is set and to guarantee that it's necessary to set DEAD and
check DEAD in rq alloc/issue paths.
blk_get_queue() is inherently opportunistic as holding a reference
doesn't prevent it from being killed. It doesn't make any sense to
require its holder to grab spinlock - either the caller doesn't need a
refcnt (as it's holding spinlock) or the result of the check becomes
stale as soon as it drops the spinlock. Whether testing DEAD is
helpful (it isn't necessary per-se) is another question tho.
Thanks.
--
tejun
next prev parent reply other threads:[~2011-10-26 19:25 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-26 1:02 [PATCHSET block:for-3.2/core] further updates to blk_cleanup_queue(), take#2 Tejun Heo
2011-10-26 1:02 ` [PATCH 1/6] block, sx8: kill blk_insert_request() Tejun Heo
2011-10-26 1:19 ` Jeff Garzik
2011-10-26 8:12 ` Jens Axboe
2011-10-26 1:02 ` [PATCH 2/6] block: allow blk_execute_rq_nowait() to be called from IRQ context Tejun Heo
2011-10-26 8:11 ` Jens Axboe
2011-10-26 19:21 ` Tejun Heo
2011-10-26 1:02 ` [PATCH 3/6] block, ide: unexport elv_add_request() Tejun Heo
2011-10-26 1:02 ` [PATCH 4/6] block: add blk_queue_dead() Tejun Heo
2011-10-26 8:18 ` Jens Axboe
2011-10-26 17:20 ` Vivek Goyal
2011-10-26 19:25 ` Tejun Heo [this message]
2011-10-26 1:02 ` [PATCH 5/6] block: fix drain_all condition in blk_drain_queue() Tejun Heo
2011-10-26 1:02 ` [PATCH 6/6] block: add missing blk_queue_dead() checks Tejun Heo
-- strict thread matches above, loose matches on Subject: below --
2011-10-21 3:56 [PATCHSET block:for-3.2/core] further updates to blk_cleanup_queue() Tejun Heo
2011-10-21 3:56 ` [PATCH 4/6] block: add blk_queue_dead() Tejun Heo
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