From: David Vrabel <david.vrabel@citrix.com>
To: Juergen Gross <jgross@suse.com>, Jan Beulich <JBeulich@suse.com>
Cc: <jejb@linux.vnet.ibm.com>, <linux-scsi@vger.kernel.org>,
<martin.petersen@oracle.com>, <lambert.quentin@gmail.com>,
<linux-kernel@vger.kernel.org>, <xen-devel@lists.xenproject.org>,
<boris.ostrovsky@oracle.com>, <dan.carpenter@oracle.com>
Subject: Re: [Xen-devel] [PATCH] xen/scsifront: don't advance ring request pointer in case of error
Date: Tue, 29 Nov 2016 11:28:39 +0000 [thread overview]
Message-ID: <de9639d9-620a-beac-7a58-14939c2baa0f@citrix.com> (raw)
In-Reply-To: <cbf7fc2e-09e4-f2ef-3fa3-5371be08270d@suse.com>
On 29/11/16 11:19, Juergen Gross wrote:
> On 29/11/16 12:14, Jan Beulich wrote:
>>>>> On 29.11.16 at 11:50, <JGross@suse.com> wrote:
>>> --- a/drivers/scsi/xen-scsifront.c
>>> +++ b/drivers/scsi/xen-scsifront.c
>>> @@ -184,8 +184,6 @@ static struct vscsiif_request *scsifront_pre_req(struct vscsifrnt_info *info)
>>>
>>> ring_req = RING_GET_REQUEST(&(info->ring), ring->req_prod_pvt);
>>>
>>> - ring->req_prod_pvt++;
>>
>> Please note the "_pvt" suffix, which stands for "private": This field is
>> not visible to the backend. Only ring->sring fields are shared, and
>> the updating of the shared field happens in RING_PUSH_REQUESTS()
>> and RING_PUSH_REQUESTS_AND_CHECK_NOTIFY().
>
> Sure, but RING_PUSH_REQUESTS() will copy req_prod_pvt to req_prod. In
> the case corrected this would advance req_prod by two after the error
> case before, even if only one request would have made it to the ring.
>
> As an alternative I could have decremented req_prod_pvt in case of an
> error, but I like my current solution better.
FWIW, I found the commit message a bit misleading and also came to the
same conclusion as Jan initially.
Perhaps,
"When adding a new request to the ring, an error may cause the
(partially constructed) request to be discarded and used for the next.
Thus ring->req_prod_pvt should not be advanced until we know the request
will be successfully added to the ring."
Or similar.
David
next prev parent reply other threads:[~2016-11-29 11:30 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-19 18:22 [PATCH] xen-scsifront: Add a missing call to kfree Quentin Lambert
2016-11-21 6:01 ` Juergen Gross
2016-11-22 3:40 ` Martin K. Petersen
2016-11-22 5:19 ` Juergen Gross
2016-11-25 21:28 ` Dan Carpenter
2016-11-29 10:50 ` [PATCH] xen/scsifront: don't advance ring request pointer in case of error Juergen Gross
2016-11-29 11:14 ` [Xen-devel] " Jan Beulich
[not found] ` <583D712F0200007800123283@suse.com>
2016-11-29 11:19 ` Juergen Gross
2016-11-29 11:28 ` David Vrabel [this message]
2016-11-29 11:33 ` Juergen Gross
2016-11-29 11:40 ` Jan Beulich
[not found] ` <583D772D02000078001232DD@suse.com>
2016-11-29 12:33 ` Juergen Gross
2016-12-02 6:10 ` [PATCH v2] xen/scsifront: don't request a slot on the ring until request is ready Juergen Gross
2016-12-02 6:13 ` Juergen Gross
2016-12-02 6:15 ` Juergen Gross
2016-12-05 15:32 ` Boris Ostrovsky
2016-12-05 15:35 ` Juergen Gross
2016-12-08 14:56 ` Boris Ostrovsky
2016-12-09 10:13 ` Juergen Gross
2016-12-05 20:53 ` [PATCH] xen-scsifront: Add a missing call to kfree Dan Carpenter
2016-12-06 5:45 ` Juergen Gross
2016-12-06 10:22 ` Dan Carpenter
2016-11-24 8:24 ` Juergen Gross
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