[PATCH] lockdep: better lock debugging

Generic lock debugging:

 - generalized lock debugging framework. For example, a bug in one lock
   subsystem turns off debugging in all lock subsystems.

 - got rid of the caller address passing (__IP__/__IP_DECL__/etc.) from
   the mutex/rtmutex debugging code: it caused way too much prototype
   hackery, and lockdep will give the same information anyway.

 - ability to do silent tests

 - check lock freeing in vfree too.

 - more finegrained debugging options, to allow distributions to
   turn off more expensive debugging features.

There's no separate 'held mutexes' list anymore - but there's a 'held locks'
stack within lockdep, which unifies deadlock detection across all lock
classes.  (this is independent of the lockdep validation stuff - lockdep first
checks whether we are holding a lock already)

Here are the current debugging options:

CONFIG_DEBUG_MUTEXES=y
CONFIG_DEBUG_LOCK_ALLOC=y

which do:

 config DEBUG_MUTEXES
          bool "Mutex debugging, basic checks"

 config DEBUG_LOCK_ALLOC
         bool "Detect incorrect freeing of live mutexes"

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 72 insertions, 37 deletions

diff --git a/lib/Makefile b/lib/Makefile
index 10c13c9d7824..4f5d01922f82 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -11,7 +11,7 @@ lib-$(CONFIG_SMP) += cpumask.o
 
 lib-y   += kobject.o kref.o kobject_uevent.o klist.o
 
-obj-y += sort.o parser.o halfmd4.o iomap_copy.o
+obj-y += sort.o parser.o halfmd4.o iomap_copy.o debug_locks.o
 
 ifeq ($(CONFIG_DEBUG_KOBJECT),y)
 CFLAGS_kobject.o += -DDEBUG
diff --git a/lib/debug_locks.c b/lib/debug_locks.c
new file mode 100644
index 000000000000..0ef01d14727c
--- /dev/null
+++ b/lib/debug_locks.c
@@ -0,0 +1,45 @@
+/*
+ * lib/debug_locks.c
+ *
+ * Generic place for common debugging facilities for various locks:
+ * spinlocks, rwlocks, mutexes and rwsems.
+ *
+ * Started by Ingo Molnar:
+ *
+ *  Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
+ */
+#include <linux/rwsem.h>
+#include <linux/mutex.h>
+#include <linux/module.h>
+#include <linux/spinlock.h>
+#include <linux/debug_locks.h>
+
+/*
+ * We want to turn all lock-debugging facilities on/off at once,
+ * via a global flag. The reason is that once a single bug has been
+ * detected and reported, there might be cascade of followup bugs
+ * that would just muddy the log. So we report the first one and
+ * shut up after that.
+ */
+int debug_locks = 1;
+
+/*
+ * The locking-testsuite uses <debug_locks_silent> to get a
+ * 'silent failure': nothing is printed to the console when
+ * a locking bug is detected.
+ */
+int debug_locks_silent;
+
+/*
+ * Generic 'turn off all lock debugging' function:
+ */
+int debug_locks_off(void)
+{
+        if (xchg(&debug_locks, 0)) {
+                if (!debug_locks_silent) {
+                        console_verbose();
+                        return 1;
+                }
+        }
+        return 0;
+}
diff --git a/lib/spinlock_debug.c b/lib/spinlock_debug.c
index 93c15ee3f8ea..3de2ccf48ac6 100644
--- a/lib/spinlock_debug.c
+++ b/lib/spinlock_debug.c
@@ -8,38 +8,35 @@
 
 #include <linux/spinlock.h>
 #include <linux/interrupt.h>
+#include <linux/debug_locks.h>
 #include <linux/delay.h>
+#include <linux/module.h>
 
 static void spin_bug(spinlock_t *lock, const char *msg)
 {
-        static long print_once = 1;
         struct task_struct *owner = NULL;
 
-        if (xchg(&print_once, 0)) {
-                if (lock->owner && lock->owner != SPINLOCK_OWNER_INIT)
-                        owner = lock->owner;
-                printk(KERN_EMERG "BUG: spinlock %s on CPU#%d, %s/%d\n",
-                        msg, raw_smp_processor_id(),
-                        current->comm, current->pid);
-                printk(KERN_EMERG " lock: %p, .magic: %08x, .owner: %s/%d, "
-                                ".owner_cpu: %d\n",
-                        lock, lock->magic,
-                        owner ? owner->comm : "<none>",
-                        owner ? owner->pid : -1,
-                        lock->owner_cpu);
-                dump_stack();
-#ifdef CONFIG_SMP
-                /*
-                 * We cannot continue on SMP:
-                 */
-//              panic("bad locking");
-#endif
-        }
+        if (!debug_locks_off())
+                return;
+
+        if (lock->owner && lock->owner != SPINLOCK_OWNER_INIT)
+                owner = lock->owner;
+        printk(KERN_EMERG "BUG: spinlock %s on CPU#%d, %s/%d\n",
+                msg, raw_smp_processor_id(),
+                current->comm, current->pid);
+        printk(KERN_EMERG " lock: %p, .magic: %08x, .owner: %s/%d, "
+                        ".owner_cpu: %d\n",
+                lock, lock->magic,
+                owner ? owner->comm : "<none>",
+                owner ? owner->pid : -1,
+                lock->owner_cpu);
+        dump_stack();
 }
 
 #define SPIN_BUG_ON(cond, lock, msg) if (unlikely(cond)) spin_bug(lock, msg)
 
-static inline void debug_spin_lock_before(spinlock_t *lock)
+static inline void
+debug_spin_lock_before(spinlock_t *lock)
 {
         SPIN_BUG_ON(lock->magic != SPINLOCK_MAGIC, lock, "bad magic");
         SPIN_BUG_ON(lock->owner == current, lock, "recursion");
@@ -118,20 +115,13 @@ void _raw_spin_unlock(spinlock_t *lock)
 
 static void rwlock_bug(rwlock_t *lock, const char *msg)
 {
-        static long print_once = 1;
-
-        if (xchg(&print_once, 0)) {
-                printk(KERN_EMERG "BUG: rwlock %s on CPU#%d, %s/%d, %p\n",
-                        msg, raw_smp_processor_id(), current->comm,
-                        current->pid, lock);
-                dump_stack();
-#ifdef CONFIG_SMP
-                /*
-                 * We cannot continue on SMP:
-                 */
-                panic("bad locking");
-#endif
-        }
+        if (!debug_locks_off())
+                return;
+
+        printk(KERN_EMERG "BUG: rwlock %s on CPU#%d, %s/%d, %p\n",
+                msg, raw_smp_processor_id(), current->comm,
+                current->pid, lock);
+        dump_stack();
 }
 
 #define RWLOCK_BUG_ON(cond, lock, msg) if (unlikely(cond)) rwlock_bug(lock, msg)