[Qemu-block] [PATCH] aio: Remove spurious smp_read_barrier_depends()

[Pranith Kumar]

smp_read_barrier_depends() should be used only if you are reading
dependent pointers which are shared. Here 'bh' is a local variable and
dereferencing it will always be ordered after loading 'bh', i.e.,
bh->next will always be ordered after fetching bh.

This patch removes the barrier and adds a comment why storing
'bh->next' is necessary.

Signed-off-by: Pranith Kumar <address@hidden>
---
 async.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/async.c b/async.c
index 3bca9b0..6b691aa 100644
--- a/async.c
+++ b/async.c
@@ -77,8 +77,7 @@ int aio_bh_poll(AioContext *ctx)
 
     ret = 0;
     for (bh = ctx->first_bh; bh; bh = next) {
-        /* Make sure that fetching bh happens before accessing its members */
-        smp_read_barrier_depends();
+        /* store bh->next since bh can be freed in aio_bh_call() */
         next = bh->next;
         /* The atomic_xchg is paired with the one in qemu_bh_schedule.  The
          * implicit memory barrier ensures that the callback sees all writes
-- 
2.9.3