[media] v4l2-ctrls: eliminate lockdep false alarms for struct v4l2_ctrl_handler.lock
When calling v4l2_ctrl_add_handler(), lockdep would detect a potential
recursive locking problem on a situation that is by design intended and
not a recursive lock. This happened because all struct
v4l2_ctrl_handler.lock mutexes were created as members of the same lock
class in v4l2_ctrl_handler_init(), and v4l2_ctrl_add_handler() takes the
hdl->lock on two different v4l2_ctrl_handler instances.
This change breaks the large lockdep lock class for struct
v4l2_ctrl_handler.lock and breaks it into v4l2_ctrl_handler
instantiation specific lock classes with meaningful class names.
This will validly eliminate lockdep alarms for v4l2_ctrl_handler locking
validation, as long as the relationships between drivers adding v4l2
controls to their own handler from other v4l2 drivers' control handlers
remains straightforward.
struct v4l2_ctrl_handler.lock lock classes are created with names such
that the output of cat /proc/lockdep indicates where in the v4l2 driver
code v4l2_ctrl_handle_init() is being called on instantiations:
ffffffffa045f490 FD: 10 BD: 8 +.+...: cx2341x:1534:(hdl)->lock
ffffffffa0497d20 FD: 12 BD: 2 +.+.+.: saa7115:1581:(hdl)->lock
ffffffffa04ac660 FD: 14 BD: 2 +.+.+.: msp3400_driver:756:(hdl)->lock
ffffffffa0484b90 FD: 12 BD: 1 +.+.+.: ivtv_gpio:366:(&itv->hdl_gpio)->lock
ffffffffa04eb530 FD: 11 BD: 2 +.+.+.: cx25840_core:1982:(&state->hdl)->lock
ffffffffa04fbc80 FD: 11 BD: 3 +.+.+.: wm8775:246:(&state->hdl)->lock
Some lock chains, that were previously causing the recursion alarms, are
now visible in the output of cat /proc/lockdep_chains:
irq_context: 0
[ffffffffa0497d20] saa7115:1581:(hdl)->lock
[ffffffffa045f490] cx2341x:1534:(hdl)->lock
irq_context: 0
[ffffffffa04ac660] msp3400_driver:756:(hdl)->lock
[ffffffffa045f490] cx2341x:1534:(hdl)->lock
irq_context: 0
[ffffffffa0484b90] ivtv_gpio:366:(&itv->hdl_gpio)->lock
[ffffffffa045f490] cx2341x:1534:(hdl)->lock
irq_context: 0
[ffffffffa04eb530] cx25840_core:1982:(&state->hdl)->lock
[ffffffffa045f490] cx2341x:1534:(hdl)->lock
irq_context: 0
[ffffffffa04fbc80] wm8775:246:(&state->hdl)->lock
[ffffffffa045f490] cx2341x:1534:(hdl)->lock
Signed-off-by: Andy Walls <awalls@md.metrocast.net>
[hans.verkuil@cisco.com: keep mutex_init in v4l2_ctrl_handler_init_class]
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/include/media/v4l2-ctrls.h b/include/media/v4l2-ctrls.h
index f00d42b..7343a27 100644
--- a/include/media/v4l2-ctrls.h
+++ b/include/media/v4l2-ctrls.h
@@ -259,7 +259,7 @@
s32 *min, s32 *max, s32 *step, s32 *def, u32 *flags);
-/** v4l2_ctrl_handler_init() - Initialize the control handler.
+/** v4l2_ctrl_handler_init_class() - Initialize the control handler.
* @hdl: The control handler.
* @nr_of_controls_hint: A hint of how many controls this handler is
* expected to refer to. This is the total number, so including
@@ -268,12 +268,35 @@
* are allocated) or the control lookup becomes slower (not enough
* buckets are allocated, so there are more slow list lookups).
* It will always work, though.
+ * @key: Used by the lock validator if CONFIG_LOCKDEP is set.
+ * @name: Used by the lock validator if CONFIG_LOCKDEP is set.
*
* Returns an error if the buckets could not be allocated. This error will
* also be stored in @hdl->error.
+ *
+ * Never use this call directly, always use the v4l2_ctrl_handler_init
+ * macro that hides the @key and @name arguments.
*/
-int v4l2_ctrl_handler_init(struct v4l2_ctrl_handler *hdl,
- unsigned nr_of_controls_hint);
+int v4l2_ctrl_handler_init_class(struct v4l2_ctrl_handler *hdl,
+ unsigned nr_of_controls_hint,
+ struct lock_class_key *key, const char *name);
+
+#ifdef CONFIG_LOCKDEP
+#define v4l2_ctrl_handler_init(hdl, nr_of_controls_hint) \
+( \
+ ({ \
+ static struct lock_class_key _key; \
+ v4l2_ctrl_handler_init_class(hdl, nr_of_controls_hint, \
+ &_key, \
+ KBUILD_BASENAME ":" \
+ __stringify(__LINE__) ":" \
+ "(" #hdl ")->_lock"); \
+ }) \
+)
+#else
+#define v4l2_ctrl_handler_init(hdl, nr_of_controls_hint) \
+ v4l2_ctrl_handler_init_class(hdl, nr_of_controls_hint, NULL, NULL)
+#endif
/** v4l2_ctrl_handler_free() - Free all controls owned by the handler and free
* the control list.