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Subject: Re: [Qemu-devel] Hang in aio/multi/mutex/mcs
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To: =?UTF-8?Q?Alex_Benn=c3=a9e?= <alex.bennee@linaro.org>, Stefan Hajnoczi <stefanha@gmail.com>
Cc: qemu-devel <qemu-devel@nongnu.org>



On 23/02/2017 20:48, Alex Bennée wrote:
> Hope that helps the debugging ;-)

Worst case we can just remove the test (it's only there for performance
comparison, not a bug in actual QEMU code), but this seems to help here:

diff --git a/tests/test-aio-multithread.c b/tests/test-aio-multithread.c
index f11e990..8b0b40e 100644
--- a/tests/test-aio-multithread.c
+++ b/tests/test-aio-multithread.c
@@ -309,7 +309,7 @@ static void mcs_mutex_lock(void)
 static void mcs_mutex_unlock(void)
 {
     int next;
-    if (nodes[id].next == -1) {
+    if (atomic_read(&nodes[id].next) == -1) {
         if (atomic_read(&mutex_head) == id &&
             atomic_cmpxchg(&mutex_head, id, -1) == id) {
             /* Last item in the list, exit.  */
@@ -323,7 +323,7 @@ static void mcs_mutex_unlock(void)
     }

     /* Wake up the next in line.  */
-    next = nodes[id].next;
+    next = atomic_read(&nodes[id].next);
     nodes[next].locked = 0;
     qemu_futex_wake(&nodes[next].locked, 1);
 }

Paolo