[PATCH] Doc/lockdep-design: explain display of {state-bits}
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/Documentation/lockdep-design.txt b/Documentation/lockdep-design.txt
index 00d9360..55a7e4f 100644
--- a/Documentation/lockdep-design.txt
+++ b/Documentation/lockdep-design.txt
@@ -36,6 +36,28 @@
- 'ever used' [ == !unused ]
+When locking rules are violated, these 4 state bits are presented in the
+locking error messages, inside curlies. A contrived example:
+
+ modprobe/2287 is trying to acquire lock:
+ (&sio_locks[i].lock){--..}, at: [<c02867fd>] mutex_lock+0x21/0x24
+
+ but task is already holding lock:
+ (&sio_locks[i].lock){--..}, at: [<c02867fd>] mutex_lock+0x21/0x24
+
+
+The bit position indicates hardirq, softirq, hardirq-read,
+softirq-read respectively, and the character displayed in each
+indicates:
+
+ '.' acquired while irqs enabled
+ '+' acquired in irq context
+ '-' acquired in process context with irqs disabled
+ '?' read-acquired both with irqs enabled and in irq context
+
+Unused mutexes cannot be part of the cause of an error.
+
+
Single-lock state rules:
------------------------
