> -----Original Message----- > From: Vitaly Kuznetsov [mailto:vkuzn...@redhat.com] > Sent: Tuesday, January 20, 2015 23:45 PM > To: KY Srinivasan; de...@linuxdriverproject.org > Cc: Haiyang Zhang; linux-kernel@vger.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 <rkrc...@redhat.com> > Signed-off-by: Vitaly Kuznetsov <vkuzn...@redhat.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. Thanks, -- Dexuan
