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-rw-r--r--drivers/hv/ring_buffer.c32
1 files changed, 30 insertions, 2 deletions
diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index f29981764653..a9021f13379f 100644
--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -29,6 +29,7 @@
#include <linux/uio.h>
#include <linux/vmalloc.h>
#include <linux/slab.h>
+#include <linux/prefetch.h>
#include "hyperv_vmbus.h"
@@ -357,7 +358,7 @@ struct vmpacket_descriptor *hv_pkt_iter_first(struct vmbus_channel *channel)
{
struct hv_ring_buffer_info *rbi = &channel->inbound;
- /* set state for later hv_signal_on_read() */
+ /* set state for later hv_pkt_iter_close */
rbi->cached_read_index = rbi->ring_buffer->read_index;
if (hv_pkt_iter_avail(rbi) < sizeof(struct vmpacket_descriptor))
@@ -400,6 +401,8 @@ EXPORT_SYMBOL_GPL(__hv_pkt_iter_next);
void hv_pkt_iter_close(struct vmbus_channel *channel)
{
struct hv_ring_buffer_info *rbi = &channel->inbound;
+ u32 cur_write_sz, cached_write_sz;
+ u32 pending_sz;
/*
* Make sure all reads are done before we update the read index since
@@ -409,6 +412,31 @@ void hv_pkt_iter_close(struct vmbus_channel *channel)
virt_rmb();
rbi->ring_buffer->read_index = rbi->priv_read_index;
- hv_signal_on_read(channel);
+ /*
+ * 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.
+ */
+ virt_mb();
+
+ pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz);
+ /* If the other end is not blocked on write don't bother. */
+ if (pending_sz == 0)
+ return;
+
+ cur_write_sz = hv_get_bytes_to_write(rbi);
+
+ if (cur_write_sz < pending_sz)
+ return;
+
+ cached_write_sz = hv_get_cached_bytes_to_write(rbi);
+ if (cached_write_sz < pending_sz)
+ vmbus_setevent(channel);
}
EXPORT_SYMBOL_GPL(hv_pkt_iter_close);