From: Mike Snitzer <snitzer@redhat.com>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
axboe@kernel.dk, linux-kernel@vger.kernel.org,
martin.petersen@oracle.com, hch@infradead.org,
dm-devel@redhat.com
Subject: Re: virtio_blk: fix defaults for max_hw_sectors and max_segment_size
Date: Wed, 26 Nov 2014 09:10:59 -0500 [thread overview]
Message-ID: <20141126141058.GA29855@redhat.com> (raw)
In-Reply-To: <87bnnuy03g.fsf@rustcorp.com.au>
On Wed, Nov 26 2014 at 12:58am -0500,
Rusty Russell <rusty@rustcorp.com.au> wrote:
> Mike Snitzer <snitzer@redhat.com> writes:
> > On Thu, Nov 20 2014 at 3:30pm -0500,
> > Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> >> On Thu, Nov 20, 2014 at 02:00:59PM -0500, Mike Snitzer wrote:
> >> > virtio_blk incorrectly established -1U as the default for these
> >> > queue_limits. Set these limits to sane default values to avoid crashing
> >> > the kernel.
> > ...
> >> > Attempting to mkfs.xfs against a thin device from this thin-pool quickly
> >> > resulted in fs/direct-io.c:dio_send_cur_page()'s BUG_ON.
> >>
> >> Why exactly does it BUG_ON?
> >> Did some memory allocation fail?
> >
> > No idea, kernel log doesn't say.. all it has is "kernel BUG" pointing to
> > fs/direct-io.c:dio_send_cur_page()'s BUG_ON.
> >
> > I could dig deeper on _why_ but honestly, there really isn't much point.
>
> There is *always* a point in understanding the code you are modifying.
Yes, I agree (and understanding the BUG in question will be pursued).
But in the context of the patch I proposed it was irrelevent.
virtio-blk still _should_ fix its limits to reflect those of the block
device it stacks on. My patch was a stop-gap until proper virtio-blk
protocol extensions were added. But you don't seem inclined to care.
> > virtio-blk doesn't get to live in fantasy-land just because it happens
> > to think it is limitless.
>
> Calm down please.
Sure, but it'd have helped if virtio-blk developers demonstrated
acknowledgement that a stacking block driver should stack the limits of
the underlying device. Instead you decided to trim all related portions
of my reply to mst that were measured and helpful.
> We don't have a sector limit. We have a segment limit, which is set
> above this line.
Then at a minimum max_hw_sectors should reflect that segment limit.
But again, the underlying device has limits that should be stacked up.
Why is that irrelevent to virtio-blk? Plus, this is a matter of not
allowing a user to shoot themselves in the foot by fiddling with
traditional block limits only to find in some kernel (*cough* RHEL6)
they result in BUG.
Mike
next prev parent reply other threads:[~2014-11-26 14:11 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-20 19:00 [PATCH] virtio_blk: fix defaults for max_hw_sectors and max_segment_size Mike Snitzer
2014-11-20 20:30 ` Michael S. Tsirkin
2014-11-20 21:15 ` Mike Snitzer
2014-11-26 5:58 ` Rusty Russell
2014-11-26 14:10 ` Mike Snitzer [this message]
2014-11-21 1:59 ` Mike Snitzer
2014-11-21 2:11 ` [PATCH v2] " Mike Snitzer
2014-11-21 9:54 ` [PATCH] " Christoph Hellwig
2014-11-21 15:49 ` Mike Snitzer
2014-11-26 19:48 ` Jens Axboe
2014-11-26 20:51 ` Mike Snitzer
2014-11-26 20:54 ` Jens Axboe
2014-11-26 21:51 ` Mike Snitzer
2014-11-26 21:53 ` Jens Axboe
2014-11-26 23:00 ` Mike Snitzer
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