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tests-aio-multithread: use atomic_read properly 

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 <alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Tested-by: Greg Kurz <groug@kaod.org>
Message-id: 20170227111726.9237-1-pbonzini@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Paolo Bonzini 2017-02-27 12:17:26 +01:00 committed by Peter Maydell
parent d992f2f136
commit 3b1d816984
1 changed files with 2 additions and 2 deletions
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4
tests/test-aio-multithread.c
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@ -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);
}