Commit 3b1d8169 authored by Paolo Bonzini's avatar Paolo Bonzini Committed by Peter Maydell
Browse files

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: default avatarAlex Bennée <alex.bennee@linaro.org>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Tested-by: default avatarGreg Kurz <groug@kaod.org>
Message-id: 20170227111726.9237-1-pbonzini@redhat.com
Signed-off-by: default avatarPeter Maydell <peter.maydell@linaro.org>
parent d992f2f1

tests/test-aio-multithread.c

+2 −2
Original line number Diff line number Diff line
@@ -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);

}