-----Original Message-----
From: Vitaly Kuznetsov [mailto:vkuznets@xxxxxxxxxx]
Sent: Tuesday, January 20, 2015 23:45 PM
To: KY Srinivasan; devel@xxxxxxxxxxxxxxxxxxxxxx
Cc: Haiyang Zhang; linux-kernel@xxxxxxxxxxxxxxx; 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@xxxxxxxxxx>
Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
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);
}
/*
--
