tree 91238d1cc9d66a0bb118ec910f9be75cbe05f865
parent bbca503b2ee000b5743a49c4995316cc499f44c6
author K. Y. Srinivasan <kys@microsoft.com> 1459639058 -0700
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> 1462050016 -0700

Drivers: hv: vmbus: Fix signaling logic in hv_need_to_signal_on_read()

On the consumer side, we have interrupt driven flow management of the
producer. It is sufficient to base the signaling decision on the
amount of space that is available to write after the read is complete.
The current code samples the previous available space and uses this
in making the signaling decision. This state can be stale and is
unnecessary. Since the state can be stale, we end up not signaling
the host (when we should) and this can result in a hang. Fix this
problem by removing the unnecessary check. I would like to thank
Arseney Romanenko <arseneyr@microsoft.com> for pointing out this issue.

Also, issue a full memory barrier before making the signaling descision
to correctly deal with potential reordering of the write (read index)
followed by the read of pending_sz.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Tested-by: Dexuan Cui <decui@microsoft.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>