Merge branch 'dtc-update' into dt/next

1 files changed, 15 insertions, 6 deletions

diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index 38ece035039e..d880296245c5 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -379,6 +379,14 @@ queue:
         tail = encode_tail(smp_processor_id(), idx);
 
         node += idx;
+
+        /*
+         * Ensure that we increment the head node->count before initialising
+         * the actual node. If the compiler is kind enough to reorder these
+         * stores, then an IRQ could overwrite our assignments.
+         */
+        barrier();
+
         node->locked = 0;
         node->next = NULL;
         pv_init_node(node);
@@ -408,14 +416,15 @@ queue:
          */
         if (old & _Q_TAIL_MASK) {
                 prev = decode_tail(old);
+
                 /*
-                 * The above xchg_tail() is also a load of @lock which
-                 * generates, through decode_tail(), a pointer.  The address
-                 * dependency matches the RELEASE of xchg_tail() such that
-                 * the subsequent access to @prev happens after.
+                 * We must ensure that the stores to @node are observed before
+                 * the write to prev->next. The address dependency from
+                 * xchg_tail is not sufficient to ensure this because the read
+                 * component of xchg_tail is unordered with respect to the
+                 * initialisation of @node.
                  */
-
-                WRITE_ONCE(prev->next, node);
+                smp_store_release(&prev->next, node);
 
                 pv_wait_node(node, prev);
                 arch_mcs_spin_lock_contended(&node->locked);