From 3b1d8169844fafee184366b0e0d7080534758b4d Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Mon, 27 Feb 2017 12:17:26 +0100 Subject: [PATCH] tests-aio-multithread: use atomic_read properly MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit nodes[id].next is written by other threads. If atomic_read is not used (matching atomic_set in mcs_mutex_lock!) the compiler can optimize the whole "if" away! Reported-by: Alex Bennée Signed-off-by: Paolo Bonzini Tested-by: Greg Kurz Message-id: 20170227111726.9237-1-pbonzini@redhat.com Signed-off-by: Peter Maydell --- tests/test-aio-multithread.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/tests/test-aio-multithread.c b/tests/test-aio-multithread.c index f11e990568..8b0b40ec78 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); }