diff options
Diffstat (limited to 'drivers/hv/channel_mgmt.c')
| -rw-r--r-- | drivers/hv/channel_mgmt.c | 21 |
1 files changed, 16 insertions, 5 deletions
diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c index 3a5700c8486a..0ced32ef2715 100644 --- a/drivers/hv/channel_mgmt.c +++ b/drivers/hv/channel_mgmt.c @@ -1028,11 +1028,22 @@ static void vmbus_onoffer_rescind(struct vmbus_channel_message_header *hdr) * offer comes in first and then the rescind. * Since we process these events in work elements, * and with preemption, we may end up processing - * the events out of order. Given that we handle these - * work elements on the same CPU, this is possible only - * in the case of preemption. In any case wait here - * until the offer processing has moved beyond the - * point where the channel is discoverable. + * the events out of order. We rely on the synchronization + * provided by offer_in_progress and by channel_mutex for + * ordering these events: + * + * { Initially: offer_in_progress = 1 } + * + * CPU1 CPU2 + * + * [vmbus_process_offer()] [vmbus_onoffer_rescind()] + * + * LOCK channel_mutex WAIT_ON offer_in_progress == 0 + * DECREMENT offer_in_progress LOCK channel_mutex + * INSERT chn_list SEARCH chn_list + * UNLOCK channel_mutex UNLOCK channel_mutex + * + * Forbids: CPU2's SEARCH from *not* seeing CPU1's INSERT */ while (atomic_read(&vmbus_connection.offer_in_progress) != 0) { |