From: Jens Axboe <axboe@suse.de>
To: Bharata B Rao <bharata@in.ibm.com>
Cc: "Martin J. Bligh" <mbligh@aracnet.com>,
Adrian Bunk <bunk@fs.tum.de>,
linux-kernel <linux-kernel@vger.kernel.org>,
Suparna Bhattacharya <suparna@in.ibm.com>
Subject: Re: 2.5.69-mjb1: undefined reference to `blk_queue_empty'
Date: Wed, 14 May 2003 10:32:24 +0200 [thread overview]
Message-ID: <20030514083224.GC13456@suse.de> (raw)
In-Reply-To: <20030514133843.H31823@in.ibm.com>
On Wed, May 14 2003, Bharata B Rao wrote:
> On Tue, May 13, 2003 at 08:11:55PM +0200, Jens Axboe wrote:
> > > >
> > > > /* For now we assume we have the device to ourselves */
> > > > /* Just a quick sanity check */
> > > > - if (!blk_queue_empty(bdev_get_queue(dump_bdev->bdev))) {
> > > > + if (elv_next_request(bdev_get_queue(dump_bdev->bdev))) {
> > > > /* i/o in flight - safer to quit */
> > > > return -EBUSY;
> > > > }
> >
> > this looks horribly racy (of the io scheduler internals corrupting
> > kind), I don't see you holding the queue lock here. some io schedulers
> > do non-significant amount of work inside they next_request functions,
> > moving from back-end lists to dispatch queue.
> >
>
> Jens,
>
> All we want to do here is to check if there are requests in the
> queue. Hence thinking of using elv_queue_empty(). Do you think
> we still need to acquire queue lock for this ? This code will be
> run when we have stopped everything else in other cpus by putting
> them into spin.
That really has to be locked down as well. For your purpose, I think the
use of elv_queue_empty() is much better even though it really is an
internal function. The problem mainly comes from AS, that can have non
empty queue but still return NULL in elv_next_request().
But yes, it needs to be locked. If you have pinned the other CPUs, then
I suppose it should work. But it's still a violation of the locking
rules, and one would get in trouble dropping the queue lock from the io
scheduler elevator_queue_empty_fn. No one does that currently, but... So
please take the lock.
--
Jens Axboe
next prev parent reply other threads:[~2003-05-14 8:23 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-05-11 3:44 2.5.69-mjb1 Martin J. Bligh
2003-05-11 13:33 ` 2.5.69-mjb1 Zwane Mwaikambo
2003-05-11 13:12 ` 2.5.69-mjb1 Martin J. Bligh
2003-05-12 13:29 ` 2.5.69-mjb1 William Lee Irwin III
2003-05-12 12:40 ` 2.5.69-mjb1 Martin J. Bligh
2003-05-12 15:03 ` 2.5.69-mjb1 William Lee Irwin III
2003-05-12 13:07 ` 2.5.69-mjb1 Martin J. Bligh
2003-05-12 15:34 ` 2.5.69-mjb1 Dave Hansen
2003-05-12 13:43 ` 2.5.69-mjb1 Martin J. Bligh
2003-05-12 15:11 ` 2.5.69-mjb1 Dave Hansen
2003-05-12 15:05 ` 2.5.69-mjb1 Dave Hansen
2003-05-13 1:23 ` [Lse-tech] 2.5.69-mjb1 William Lee Irwin III
2003-05-13 3:41 ` Martin J. Bligh
2003-05-13 6:27 ` William Lee Irwin III
2003-05-13 6:42 ` Andi Kleen
2003-05-12 20:51 ` 2.5.69-mjb1: undefined reference to `blk_queue_empty' Adrian Bunk
2003-05-13 3:51 ` Martin J. Bligh
2003-05-13 7:18 ` Bharata B Rao
2003-05-13 13:58 ` Martin J. Bligh
2003-05-13 18:11 ` Jens Axboe
2003-05-14 8:08 ` Bharata B Rao
2003-05-14 8:32 ` Jens Axboe [this message]
2003-05-15 4:07 ` Bharata B Rao
2003-05-15 7:29 ` Jens Axboe
2003-05-15 9:16 ` Bharata B Rao
2003-05-15 12:52 ` Martin J. Bligh
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