Merge pull request #761 from soby-mathew/sm/bakery_lock_fixes

Fix normal memory bakery lock implementation

1 files changed, 21 insertions, 8 deletions

diff --git a/lib/locks/bakery/bakery_lock_normal.c b/lib/locks/bakery/bakery_lock_normal.c
index efc1b57e..5a2fb071 100644
--- a/lib/locks/bakery/bakery_lock_normal.c
+++ b/lib/locks/bakery/bakery_lock_normal.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2015-2016, ARM Limited and Contributors. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
@@ -90,6 +90,22 @@ extern void *__PERCPU_BAKERY_LOCK_SIZE__;
 #define read_cache_op(addr, cached)	if (cached) \
 					    dccivac((uintptr_t)addr)
 
+/* Helper function to check if the lock is acquired */
+static inline int is_lock_acquired(const bakery_info_t *my_bakery_info,
+							int is_cached)
+{
+	/*
+	 * Even though lock data is updated only by the owning cpu and
+	 * appropriate cache maintenance operations are performed,
+	 * if the previous update was done when the cpu was not participating
+	 * in coherency, then there is a chance that cache maintenance
+	 * operations were not propagated to all the caches in the system.
+	 * Hence do a `read_cache_op()` prior to read.
+	 */
+	read_cache_op(my_bakery_info, is_cached);
+	return !!(bakery_ticket_number(my_bakery_info->lock_data));
+}
+
 static unsigned int bakery_get_ticket(bakery_lock_t *lock,
 						unsigned int me, int is_cached)
 {
@@ -104,12 +120,8 @@ static unsigned int bakery_get_ticket(bakery_lock_t *lock,
 	my_bakery_info = get_bakery_info(me, lock);
 	assert(my_bakery_info);
 
-	/*
-	 * Prevent recursive acquisition.
-	 * Since lock data is written to and cleaned by the owning cpu, it
-	 * doesn't require any cache operations prior to reading the lock data.
-	 */
-	assert(!bakery_ticket_number(my_bakery_info->lock_data));
+	/* Prevent recursive acquisition.*/
+	assert(!is_lock_acquired(my_bakery_info, is_cached));
 
 	/*
 	 * Tell other contenders that we are through the bakery doorway i.e.
@@ -222,7 +234,8 @@ void bakery_lock_release(bakery_lock_t *lock)
 	unsigned int is_cached = read_sctlr_el3() & SCTLR_C_BIT;
 
 	my_bakery_info = get_bakery_info(plat_my_core_pos(), lock);
-	assert(bakery_ticket_number(my_bakery_info->lock_data));
+
+	assert(is_lock_acquired(my_bakery_info, is_cached));
 
 	my_bakery_info->lock_data = 0;
 	write_cache_op(my_bakery_info, is_cached);