From 8dd45f2ab005a1f3301296059b23b03ec3dbf79b Mon Sep 17 00:00:00 2001 From: Stephen Hemminger Date: Sun, 25 Jun 2017 12:30:26 -0700 Subject: vmbus: refactor hv_signal_on_read The function hv_signal_on_read was defined in hyperv.h and only used in one place in ring_buffer code. Clearer to just move it inline there. Signed-off-by: Stephen Hemminger Signed-off-by: K. Y. Srinivasan Signed-off-by: Greg Kroah-Hartman --- drivers/hv/ring_buffer.c | 32 ++++++++++++++++++++++++++++++-- 1 file changed, 30 insertions(+), 2 deletions(-) (limited to 'drivers/hv/ring_buffer.c') 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 #include #include +#include #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); -- cgit v1.2.3-55-g7522