From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: Bob Liu <bob.liu@oracle.com>
Cc: linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org,
roger.pau@citrix.com
Subject: Re: [PATCH 1/2] xen-blkfront: don't call talk_to_blkback when already connected to blkback
Date: Tue, 31 May 2016 16:33:07 -0400 [thread overview]
Message-ID: <20160531203307.GC23808@char.us.oracle.com> (raw)
In-Reply-To: <1464685157-30738-1-git-send-email-bob.liu@oracle.com>
On Tue, May 31, 2016 at 04:59:16PM +0800, Bob Liu wrote:
> Sometimes blkfont may receive twice blkback_changed() notification after
> migration, then talk_to_blkback() will be called twice too and confused
> xen-blkback.
Could you enlighten the patch description by having some form of
state transition here? I am curious how you got the frontend
to get in XenbusStateConnected (via blkif_recover right) and then
the backend triggering the update once more?
Or is just a simple race - the backend moves from XenbusStateConnected->
XenbusStateConnected - which retriggers the frontend to hit in
blkback_changed the XenbusStateConnected state and go in there?
(That would be in conenct_ring changing the state). But I don't
see how the frontend_changed code get there as we have:
770 /*
771 * Ensure we connect even when two watches fire in
772 * close succession and we miss the intermediate value
773 * of frontend_state.
774 */
775 if (dev->state == XenbusStateConnected)
776 break;
777
?
Now what about 'blkfront_connect' being called on the second time?
Ah, info->connected is probably by then in BLKIF_STATE_CONNECTED
(as blkif_recover changed) and we just reread the size of the disk.
Is that how about the flow goes?
>
> Signed-off-by: Bob Liu <bob.liu@oracle.com>
> ---
> drivers/block/xen-blkfront.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index ca13df8..01aa460 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -2485,7 +2485,8 @@ static void blkback_changed(struct xenbus_device *dev,
> break;
>
> case XenbusStateConnected:
> - if (dev->state != XenbusStateInitialised) {
> + if ((dev->state != XenbusStateInitialised) &&
> + (dev->state != XenbusStateConnected)) {
> if (talk_to_blkback(dev, info))
> break;
> }
> --
> 2.7.4
>
next prev parent reply other threads:[~2016-05-31 20:33 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-31 8:59 [PATCH 1/2] xen-blkfront: don't call talk_to_blkback when already connected to blkback Bob Liu
2016-05-31 8:59 ` [PATCH 2/2] xen-blkfront: fix resume issues Bob Liu
2016-05-31 20:33 ` Konrad Rzeszutek Wilk [this message]
2016-06-01 5:49 ` [PATCH 1/2] xen-blkfront: don't call talk_to_blkback when already connected to blkback Bob Liu
2016-06-02 14:30 ` Konrad Rzeszutek Wilk
2016-06-07 15:25 ` Konrad Rzeszutek Wilk
2016-06-08 6:46 ` Bob Liu
2016-06-08 14:47 ` Konrad Rzeszutek Wilk
2016-06-15 8:39 ` [Xen-devel] " Ross Lagerwall
2016-06-15 14:08 ` Konrad Rzeszutek Wilk
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