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Message-ID: <BY2PR0301MB071139D316E85EDA7BF842ACA03F0@BY2PR0301MB0711.namprd03.prod.outlook.com>
Date: Sun, 1 Feb 2015 18:12:19 +0000
From: KY Srinivasan <kys@...rosoft.com>
To: Jason Wang <jasowang@...hat.com>, Dexuan Cui <decui@...rosoft.com>
CC: Vitaly Kuznetsov <vkuznets@...hat.com>,
"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
Haiyang Zhang <haiyangz@...rosoft.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Radim Krčmář <rkrcmar@...hat.com>,
Dan Carpenter <dan.carpenter@...cle.com>
Subject: RE: [PATCH v3 3/3] Drivers: hv: vmbus: serialize Offer and Rescind
offer
> -----Original Message-----
> From: Jason Wang [mailto:jasowang@...hat.com]
> Sent: Thursday, January 29, 2015 2:07 AM
> To: Dexuan Cui
> Cc: Vitaly Kuznetsov; KY Srinivasan; devel@...uxdriverproject.org; Haiyang
> Zhang; linux-kernel@...r.kernel.org; Radim Krčmář; Dan Carpenter
> Subject: RE: [PATCH v3 3/3] Drivers: hv: vmbus: serialize Offer and Rescind
> offer
>
>
>
> On Wed, Jan 28, 2015 at 7:57 PM, Dexuan Cui <decui@...rosoft.com> wrote:
> >> -----Original Message-----
> >> From: Vitaly Kuznetsov [mailto:vkuznets@...hat.com]
> >> Sent: Tuesday, January 20, 2015 23:45 PM
> >> To: KY Srinivasan; devel@...uxdriverproject.org
> >> Cc: Haiyang Zhang; linux-kernel@...r.kernel.org; Dexuan Cui; Jason
> >> Wang; Radim Krčmář; Dan Carpenter
> >> Subject: [PATCH v3 3/3] Drivers: hv: vmbus: serialize Offer and
> >> Rescind offer
> >>
> >> Commit 4b2f9abea52a ("staging: hv: convert channel_mgmt.c to not
> >> call osd_schedule_callback")' was written under an assumption that
> >> we never receive Rescind offer while we're still processing the
> >> initial Offer request. However, the issue we fixed in 04a258c162a8
> >> could be caused by this assumption not always being true.
> >>
> >> In particular, we need to protect against the following:
> >> 1) Receiving a Rescind offer after we do queue_work() for processing
> >> an Offer
> >> request and before we actually enter vmbus_process_offer().
> >> work.func
> >> points
> >> to vmbus_process_offer() at this moment and in
> >> vmbus_onoffer_rescind()
> >> we do
> >> another queue_work() without a check so we'll enter
> >> vmbus_process_offer()
> >> twice.
> >> 2) Receiving a Rescind offer after we enter vmbus_process_offer()
> >> and
> >> especially after we set >state = CHANNEL_OPEN_STATE. Many things
> >> can go
> >> wrong in that case, e.g. we can call free_channel() while we're
> >> still using
> >> it.
> >>
> >> Implement the required protection by changing work->func at the very
> >> end of
> >> vmbus_process_offer() and checking work->func in
> >> vmbus_onoffer_rescind().
> >> In
> >> case we receive rescind offer during or before
> >> vmbus_process_offer() is
> >> done
> >> we set rescind flag to true and we check it at the end of
> >> vmbus_process_offer()
> >> so such offer will not get lost.
> >>
> >> Suggested-by: Radim Krčmář <rkrcmar@...hat.com>
> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> >> ---
> >> drivers/hv/channel_mgmt.c | 30 ++++++++++++++++++++++--------
> >> 1 file changed, 22 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
> >> index c6fdd74..877a944 100644
> >> --- a/drivers/hv/channel_mgmt.c
> >> +++ b/drivers/hv/channel_mgmt.c
> >> @@ -279,9 +279,6 @@ static void vmbus_process_offer(struct
> >> work_struct
> >> *work)
> >> int ret;
> >> unsigned long flags;
> >>
> >> - /* The next possible work is rescind handling */
> >> - INIT_WORK(&newchannel->work, vmbus_process_rescind_offer);
> >> -
> >> /* Make sure this is a new offer */
> >> spin_lock_irqsave(&vmbus_connection.channel_lock, flags);
> >>
> >> @@ -341,7 +338,7 @@ static void vmbus_process_offer(struct
> >> work_struct
> >> *work)
> >> if (channel->sc_creation_callback != NULL)
> >> channel->sc_creation_callback(newchannel);
> >>
> >> - goto out;
> >> + goto done_init_rescind;
> >> }
> >>
> >> goto err_free_chan;
> >> @@ -382,7 +379,14 @@ static void vmbus_process_offer(struct
> >> work_struct
> >> *work)
> >> kfree(newchannel->device_obj);
> >> goto err_free_chan;
> >> }
> >> -out:
> >> +done_init_rescind:
> >> + spin_lock_irqsave(&newchannel->lock, flags);
> >> + /* The next possible work is rescind handling */
> >> + INIT_WORK(&newchannel->work, vmbus_process_rescind_offer);
> >> + /* Check if rescind offer was already received */
> >> + if (newchannel->rescind)
> >> + queue_work(newchannel->controlwq, &newchannel-
> >work);
> >> + spin_unlock_irqrestore(&newchannel->lock, flags);
> >> return;
> >> err_free_chan:
> >> free_channel(newchannel);
> >> @@ -520,6 +524,7 @@ static void vmbus_onoffer_rescind(struct
> >> vmbus_channel_message_header *hdr)
> >> {
> >> struct vmbus_channel_rescind_offer *rescind;
> >> struct vmbus_channel *channel;
> >> + unsigned long flags;
> >>
> >> rescind = (struct vmbus_channel_rescind_offer *)hdr;
> >> channel = relid2channel(rescind->child_relid);
> >> @@ -528,11 +533,20 @@ static void vmbus_onoffer_rescind(struct
> >> vmbus_channel_message_header *hdr)
> >> /* Just return here, no channel found */
> >> return;
> >>
> >> + spin_lock_irqsave(&channel->lock, flags);
> >> channel->rescind = true;
> >> + /*
> >> + * channel->work.func != vmbus_process_rescind_offer means we
> >> are still
> >> + * processing offer request and the rescind offer processing
> >> should
> >> be
> >> + * postponed. It will be done at the very end of
> >> vmbus_process_offer()
> >> + * as rescind flag is being checked there.
> >> + */
> >> + if (channel->work.func == vmbus_process_rescind_offer)
> >> + /* work is initialized for vmbus_process_rescind_offer() from
> >> + * vmbus_process_offer() where the channel got created */
> >> + queue_work(channel->controlwq, &channel->work);
> >>
> >> - /* work is initialized for vmbus_process_rescind_offer() from
> >> - * vmbus_process_offer() where the channel got created */
> >> - queue_work(channel->controlwq, &channel->work);
> >> + spin_unlock_irqrestore(&channel->lock, flags);
> >> }
> >>
> >> /*
> >> --
> >
> > Hi Vitaly and all,
> > I have 2 questions:
> > In vmbus_process_offer(), in the cases of "goto err_free_chan",
> > should we consider the possibility a rescind message could be pending
> > for the new channel?
> > In the cases, because we don't run
> > "INIT_WORK(&newchannel->work, vmbus_process_rescind_offer); ",
> > vmbus_onoffer_rescind() will do nothing and as a result,
> > vmbus_process_rescind_offer() won't be invoked.
> >
> > Question 2: in vmbus_process_offer(), in the case
> > vmbus_device_register() fails, we'll run
> > "list_del(&newchannel->listentry);" -- just after this line, what
> > will happen at this time if relid2channel() returns NULL in
> > vmbus_onoffer_rescind()?
> >
> > I think we'll lose the rescind message.
>
> If CHANNELMSG_RELID_RELEASED is mandatory, need INIT_WORK during
> onoffer_rescind() unconditionally and and we need post this message
> without the help of relid2channel() since:
>
> - relid2channel() only valid when the channel was added to list, so either in
> the case of question 2 or before list_add_tail() in
> vmbus_process_offer()
> - the channel rescind offer message has a relid
>
Once the channel is rescinded from the host, we need to send the RELID_RELEASED message to the host
for the host to potentially resend the offer.
K. Y
> >
> >
> > Thanks,
> > -- Dexuan
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