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Date: Wed, 21 Jan 2015 03:33:27 +0008
From: Jason Wang <jasowang@...hat.com>
To: Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: "K. Y. Srinivasan" <kys@...rosoft.com>,
devel@...uxdriverproject.org,
Haiyang Zhang <haiyangz@...rosoft.com>,
linux-kernel@...r.kernel.org, Dexuan Cui <decui@...rosoft.com>,
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 Tue, Jan 20, 2015 at 11:45 PM, Vitaly Kuznetsov
<vkuznets@...hat.com> wrote:
> 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>
> ---
Acked-by: Jason Wang <jasowang@...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);
> }
>
> /*
> --
> 1.9.3
>
--
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