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[Qemu-devel] [PULL 4/4] tests-aio-multithread: use atomic_read properly
From: |
Stefan Hajnoczi |
Subject: |
[Qemu-devel] [PULL 4/4] tests-aio-multithread: use atomic_read properly |
Date: |
Mon, 27 Feb 2017 16:34:47 +0000 |
From: Paolo Bonzini <address@hidden>
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 <address@hidden>
Signed-off-by: Paolo Bonzini <address@hidden>
Tested-by: Greg Kurz <address@hidden>
Message-id: address@hidden
Signed-off-by: Stefan Hajnoczi <address@hidden>
---
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 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);
}
--
2.9.3