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@xxxxxxxxxxxxxxxx>
diff --git a/drivers/media/video/v4l2-ctrls.c b/drivers/media/video/v4l2-ctrls.c
index 9d2502c..8b7de34 100644
--- a/drivers/media/video/v4l2-ctrls.c
+++ b/drivers/media/video/v4l2-ctrls.c
@@ -761,10 +761,9 @@ static inline int handler_set_err(struct v4l2_ctrl_handler *hdl, int err)
}
/* Initialize the handler */
-int v4l2_ctrl_handler_init(struct v4l2_ctrl_handler *hdl,
- unsigned nr_of_controls_hint)
+int _v4l2_ctrl_handler_init(struct v4l2_ctrl_handler *hdl,
+ unsigned nr_of_controls_hint)
{
- mutex_init(&hdl->lock);
INIT_LIST_HEAD(&hdl->ctrls);
INIT_LIST_HEAD(&hdl->ctrl_refs);
hdl->nr_of_buckets = 1 + nr_of_controls_hint / 8;
@@ -773,7 +772,7 @@ int v4l2_ctrl_handler_init(struct v4l2_ctrl_handler *hdl,
hdl->error = hdl->buckets ? 0 : -ENOMEM;
return hdl->error;
}
-EXPORT_SYMBOL(v4l2_ctrl_handler_init);
+EXPORT_SYMBOL(_v4l2_ctrl_handler_init);
/* Free all controls and control refs */
void v4l2_ctrl_handler_free(struct v4l2_ctrl_handler *hdl)
diff --git a/include/media/v4l2-ctrls.h b/include/media/v4l2-ctrls.h
index 9b7bea9..3bc0f69 100644
--- a/include/media/v4l2-ctrls.h
+++ b/include/media/v4l2-ctrls.h
@@ -238,8 +238,21 @@ void v4l2_ctrl_fill(u32 id, const char **name, enum v4l2_ctrl_type *type,
* Returns an error if the buckets could not be allocated. This error will
* also be stored in @hdl->error.
*/
-int v4l2_ctrl_handler_init(struct v4l2_ctrl_handler *hdl,
- unsigned nr_of_controls_hint);
+int _v4l2_ctrl_handler_init(struct v4l2_ctrl_handler *hdl,
+ unsigned nr_of_controls_hint);
+
+#define v4l2_ctrl_handler_init(hdl, nr_of_controls_hint) \
+( \
+ ({ \
+ static struct lock_class_key _key; \
+ mutex_init(&(hdl)->lock); \
+ lockdep_set_class_and_name(&(hdl)->lock, &_key, \
+ KBUILD_BASENAME ":" \
+ __stringify(__LINE__) ":" \
+ "(" #hdl ")->lock"); \
+ }), \
+ _v4l2_ctrl_handler_init(hdl, nr_of_controls_hint) \
+)
/** v4l2_ctrl_handler_free() - Free all controls owned by the handler and free
* the control list.
--
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