Add missing barriers to Bakery Locks
With the current implementation, it's possible for a contender to
observe accesses in the Critical Section before acquiring or releasing
the lock. Insert fencing in the locking and release codes to prevent any
reorder.
Fixes ARM-software/tf-issues#609
Change-Id: I773b82aa41dd544a2d3dbacb9a4b42c9eb767bbb
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>
diff --git a/lib/locks/bakery/bakery_lock_coherent.c b/lib/locks/bakery/bakery_lock_coherent.c
index 788ba98..03277c3 100644
--- a/lib/locks/bakery/bakery_lock_coherent.c
+++ b/lib/locks/bakery/bakery_lock_coherent.c
@@ -1,5 +1,5 @@
/*
- * Copyright (c) 2013-2015, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2018, ARM Limited and Contributors. All rights reserved.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
@@ -133,7 +133,12 @@
bakery_ticket_number(bakery->lock_data[they]));
}
}
- /* Lock acquired */
+
+ /*
+ * Lock acquired. Ensure that any reads from a shared resource in the
+ * critical section read values after the lock is acquired.
+ */
+ dmbld();
}
@@ -146,9 +151,11 @@
assert(bakery_ticket_number(bakery->lock_data[me]));
/*
- * Release lock by resetting ticket. Then signal other
- * waiting contenders
+ * Ensure that other observers see any stores in the critical section
+ * before releasing the lock. Release the lock by resetting ticket.
+ * Then signal other waiting contenders.
*/
+ dmbst();
bakery->lock_data[me] = 0;
dsb();
sev();
diff --git a/lib/locks/bakery/bakery_lock_normal.c b/lib/locks/bakery/bakery_lock_normal.c
index 630226a..b947da9 100644
--- a/lib/locks/bakery/bakery_lock_normal.c
+++ b/lib/locks/bakery/bakery_lock_normal.c
@@ -204,7 +204,12 @@
== bakery_ticket_number(their_bakery_info->lock_data));
}
}
- /* Lock acquired */
+
+ /*
+ * Lock acquired. Ensure that any reads from a shared resource in the
+ * critical section read values after the lock is acquired.
+ */
+ dmbld();
}
void bakery_lock_release(bakery_lock_t *lock)
@@ -220,6 +225,12 @@
assert(is_lock_acquired(my_bakery_info, is_cached));
+ /*
+ * Ensure that other observers see any stores in the critical section
+ * before releasing the lock. Release the lock by resetting ticket.
+ * Then signal other waiting contenders.
+ */
+ dmbst();
my_bakery_info->lock_data = 0;
write_cache_op(my_bakery_info, is_cached);
sev();