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-rw-r--r--drivers/hv/ring_buffer.c26
1 files changed, 20 insertions, 6 deletions
diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index 5613e2b5cff7..a40a73a7b71d 100644
--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -103,15 +103,29 @@ static bool hv_need_to_signal(u32 old_write, struct hv_ring_buffer_info *rbi)
* there is room for the producer to send the pending packet.
*/
-static bool hv_need_to_signal_on_read(u32 prev_write_sz,
- struct hv_ring_buffer_info *rbi)
+static bool hv_need_to_signal_on_read(struct hv_ring_buffer_info *rbi)
{
u32 cur_write_sz;
u32 r_size;
- u32 write_loc = rbi->ring_buffer->write_index;
+ u32 write_loc;
u32 read_loc = rbi->ring_buffer->read_index;
- u32 pending_sz = rbi->ring_buffer->pending_send_sz;
+ u32 pending_sz;
+ /*
+ * Issue a full memory barrier before making the signaling decision.
+ * Here is the reason for having this barrier:
+ * If the reading of the pend_sz (in this function)
+ * were to be reordered and read before we commit the new read
+ * index (in the calling function) we could
+ * have a problem. If the host were to set the pending_sz after we
+ * have sampled pending_sz and go to sleep before we commit the
+ * read index, we could miss sending the interrupt. Issue a full
+ * memory barrier to address this.
+ */
+ mb();
+
+ pending_sz = rbi->ring_buffer->pending_send_sz;
+ write_loc = rbi->ring_buffer->write_index;
/* If the other end is not blocked on write don't bother. */
if (pending_sz == 0)
return false;
@@ -120,7 +134,7 @@ static bool hv_need_to_signal_on_read(u32 prev_write_sz,
cur_write_sz = write_loc >= read_loc ? r_size - (write_loc - read_loc) :
read_loc - write_loc;
- if ((prev_write_sz < pending_sz) && (cur_write_sz >= pending_sz))
+ if (cur_write_sz >= pending_sz)
return true;
return false;
@@ -455,7 +469,7 @@ int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info,
/* Update the read index */
hv_set_next_read_location(inring_info, next_read_location);
- *signal = hv_need_to_signal_on_read(bytes_avail_towrite, inring_info);
+ *signal = hv_need_to_signal_on_read(inring_info);
return ret;
}

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