diff options
| -rw-r--r-- | drivers/hv/ring_buffer.c | 26 |
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; } |