Drivers: hv: vmbus: Don't bind the offer&rescind works to a specific CPU (b9fa1b87) · Commits · 戴 / test

drivers/hv/channel_mgmt.c

+16 −5

Original line number	Diff line number	Diff line
		@@ -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) {

drivers/hv/vmbus_drv.c

+28 −11

Original line number	Diff line number	Diff line
		@@ -1101,8 +1101,9 @@ void vmbus_on_msg_dpc(unsigned long data)
		/*
		* The host can generate a rescind message while we
		* may still be handling the original offer. We deal with
		* this condition by ensuring the processing is done on the
		* same CPU.
		* this condition by relying on the synchronization provided
		* by offer_in_progress and by channel_mutex. See also the
		* inline comments in vmbus_onoffer_rescind().
		*/
		switch (hdr->msgtype) {
		case CHANNELMSG_RESCIND_CHANNELOFFER:
		@@ -1124,16 +1125,34 @@ void vmbus_on_msg_dpc(unsigned long data)
		* work queue: the RESCIND handler can not start to
		* run before the OFFER handler finishes.
		*/
		schedule_work_on(VMBUS_CONNECT_CPU,
		&ctx->work);
		schedule_work(&ctx->work);
		break;

		case CHANNELMSG_OFFERCHANNEL:
		/*
		* The host sends the offer message of a given channel
		* before sending the rescind message of the same
		* channel. These messages are sent to the guest's
		* connect CPU; the guest then starts processing them
		* in the tasklet handler on this CPU:
		*
		* VMBUS_CONNECT_CPU
		*
		* [vmbus_on_msg_dpc()]
		* atomic_inc() // CHANNELMSG_OFFERCHANNEL
		* queue_work()
		* ...
		* [vmbus_on_msg_dpc()]
		* schedule_work() // CHANNELMSG_RESCIND_CHANNELOFFER
		*
		* We rely on the memory-ordering properties of the
		* queue_work() and schedule_work() primitives, which
		* guarantee that the atomic increment will be visible
		* to the CPUs which will execute the offer & rescind
		* works by the time these works will start execution.
		*/
		atomic_inc(&vmbus_connection.offer_in_progress);
		queue_work_on(VMBUS_CONNECT_CPU,
		vmbus_connection.work_queue,
		&ctx->work);
		break;
		fallthrough;

		default:
		queue_work(vmbus_connection.work_queue, &ctx->work);
		@@ -1178,9 +1197,7 @@ static void vmbus_force_channel_rescinded(struct vmbus_channel *channel)

		INIT_WORK(&ctx->work, vmbus_onmessage_work);

		queue_work_on(VMBUS_CONNECT_CPU,
		vmbus_connection.work_queue,
		&ctx->work);
		queue_work(vmbus_connection.work_queue, &ctx->work);
		}
		#endif /* CONFIG_PM_SLEEP */

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