[PATCH 2/2] aio: make aio_read_events_ring be aware of aio_complete

[Gu Zheng <guz.fnst@cn.fujitsu.com>]

Commit 5ffac122dbda8(aio: Don't use ctx->tail unnecessarily) uses
ring->tail rather than the ctx->tail, but with this change, we fetch 'tail'
only once at the start, so that we can not be aware of adding event by aio_complete
when reading events. It seems a regression.
So here we fetch the ring->tail in start of the loop each time to make it be
aware of adding event from aio_complete.

Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
---
 fs/aio.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 7eaa631..f5b8551 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1029,10 +1029,14 @@ static long aio_read_events_ring(struct kioctx *ctx,
 		struct io_event *ev;
 		struct page *page;
 
-		avail = (head <= tail ?  tail : ctx->nr_events) - head;
+		ring = kmap_atomic(ctx->ring_pages[0]);
+		tail = ring->tail;
+		kunmap_atomic(ring);
+
 		if (head == tail)
 			break;
 
+		avail = (head <= tail ?  tail : ctx->nr_events) - head;
 		avail = min(avail, nr - ret);
 		avail = min_t(long, avail, AIO_EVENTS_PER_PAGE -
 			    ((head + AIO_EVENTS_OFFSET) % AIO_EVENTS_PER_PAGE));
-- 
1.7.7