From: Bob Liu <bob.liu@oracle.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
roger.pau@citrix.com
Subject: Re: [PATCH 1/2] xen-blkfront: don't call talk_to_blkback when already connected to blkback
Date: Wed, 01 Jun 2016 13:49:23 +0800 [thread overview]
Message-ID: <574E7763.9060001__35615.2870147072$1464760246$gmane$org@oracle.com> (raw)
In-Reply-To: <20160531203307.GC23808@char.us.oracle.com>
On 06/01/2016 04:33 AM, Konrad Rzeszutek Wilk wrote:
> 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?
blkfront blkback
blkfront_resume()
> talk_to_blkback()
> Set blkfront to XenbusStateInitialised
Front changed()
> Connect()
> Set blkback to XenbusStateConnected
blkback_changed()
> Skip talk_to_blkback()
because frontstate == XenbusStateInitialised
> blkfront_connect()
> Set blkfront to XenbusStateConnected
------------------------------------------------------------------
But sometimes blkfront receives
blkback_changed() event more than once!
Not sure why.
blkback_changed()
> because now frontstate != XenbusStateInitialised
talk_to_blkback() is also called again
> blkfront state changed from
XenbusStateConnected to XenbusStateInitialised
(Which is not correct!)
Front_changed():
> Do nothing because blkback
already in XenbusStateConnected
Now blkback is XenbusStateConnected but blkfront still XenbusStateInitialised.
>>
>> 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
>>
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next prev parent reply other threads:[~2016-06-01 5:49 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1464685157-30738-1-git-send-email-bob.liu@oracle.com>
2016-05-31 8:59 ` [PATCH 2/2] xen-blkfront: fix resume issues Bob Liu
2016-05-31 20:33 ` [PATCH 1/2] xen-blkfront: don't call talk_to_blkback when already connected to blkback Konrad Rzeszutek Wilk
[not found] ` <20160531203307.GC23808@char.us.oracle.com>
2016-06-01 5:49 ` Bob Liu [this message]
[not found] ` <574E7763.9060001@oracle.com>
2016-06-02 14:30 ` Konrad Rzeszutek Wilk
2016-06-07 15:25 ` Konrad Rzeszutek Wilk
[not found] ` <20160607152524.GA10281@localhost.localdomain>
2016-06-08 6:46 ` Bob Liu
[not found] ` <5757BF4E.9080307@oracle.com>
2016-06-08 14:47 ` Konrad Rzeszutek Wilk
[not found] ` <20160608144739.GD17027@char.us.oracle.com>
2016-06-15 8:39 ` Ross Lagerwall
[not found] ` <57611424.2020802@citrix.com>
2016-06-15 14:08 ` Konrad Rzeszutek Wilk
2016-05-31 8:59 Bob Liu
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