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Commit 97235e74 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'char-misc-4.16-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc 

Pull hyperv fix from Greg KH:
 "This is a single hyperv bugfix for 4.16-rc7.

  It resolves an issue with the ring-buffer signaling to resolve
  reported problems.

  It's been in linux-next for a while now with no reported issues"

* tag 'char-misc-4.16-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc:
  Drivers: hv: vmbus: Fix ring buffer signaling
parents cde00d21 655296c8

drivers/hv/ring_buffer.c

+35 −17
Original line number Diff line number Diff line
@@ -417,13 +417,24 @@ __hv_pkt_iter_next(struct vmbus_channel *channel, 
}

EXPORT_SYMBOL_GPL(__hv_pkt_iter_next);



/* How many bytes were read in this iterator cycle */

static u32 hv_pkt_iter_bytes_read(const struct hv_ring_buffer_info *rbi,

					u32 start_read_index)

{

	if (rbi->priv_read_index >= start_read_index)

		return rbi->priv_read_index - start_read_index;

	else

		return rbi->ring_datasize - start_read_index +

			rbi->priv_read_index;

}



/*

 * Update host ring buffer after iterating over packets.

 */

void hv_pkt_iter_close(struct vmbus_channel *channel)

{

	struct hv_ring_buffer_info *rbi = &channel->inbound;

	u32 orig_write_sz = hv_get_bytes_to_write(rbi);

	u32 curr_write_sz, pending_sz, bytes_read, start_read_index;



	/*

	 * Make sure all reads are done before we update the read index since
@@ -431,8 +442,12 @@ void hv_pkt_iter_close(struct vmbus_channel *channel) 
	 * is updated.

	 */

	virt_rmb();

	start_read_index = rbi->ring_buffer->read_index;

	rbi->ring_buffer->read_index = rbi->priv_read_index;



	if (!rbi->ring_buffer->feature_bits.feat_pending_send_sz)

		return;



	/*

	 * Issue a full memory barrier before making the signaling decision.

	 * Here is the reason for having this barrier:
@@ -446,26 +461,29 @@ void hv_pkt_iter_close(struct vmbus_channel *channel) 
	 */

	virt_mb();



	/* If host has disabled notifications then skip */

	if (rbi->ring_buffer->interrupt_mask)

	pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz);

	if (!pending_sz)

		return;



	if (rbi->ring_buffer->feature_bits.feat_pending_send_sz) {

		u32 pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz);

	/*

	 * Ensure the read of write_index in hv_get_bytes_to_write()

	 * happens after the read of pending_send_sz.

	 */

	virt_rmb();

	curr_write_sz = hv_get_bytes_to_write(rbi);

	bytes_read = hv_pkt_iter_bytes_read(rbi, start_read_index);



	/*

	 * If there was space before we began iteration,

		 * then host was not blocked. Also handles case where

		 * pending_sz is zero then host has nothing pending

		 * and does not need to be signaled.

	 * then host was not blocked.

	 */

		if (orig_write_sz > pending_sz)



	if (curr_write_sz - bytes_read > pending_sz)

		return;



	/* If pending write will not fit, don't give false hope. */

		if (hv_get_bytes_to_write(rbi) < pending_sz)

	if (curr_write_sz <= pending_sz)

		return;

	}



	vmbus_setevent(channel);

}