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Message-Id: <1422526034.14137.1@smtp.corp.redhat.com>
Date: Thu, 29 Jan 2015 10:15:14 +0008
From: Jason Wang <jasowang@...hat.com>
To: Dexuan Cui <decui@...rosoft.com>
Cc: Vitaly Kuznetsov <vkuznets@...hat.com>,
KY Srinivasan <kys@...rosoft.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
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
>
>
> Thanks,
> -- Dexuan
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