[PATCH v4 0/2] Fix lockdep warning with nested instances of i2c-mux

[PATCH v4 0/2] Fix lockdep warning with nested instances of i2c-mux

[Peter Rosin]

Hi!

Ping. This is almost a resend of v3, but I added tested-by tags from
John and unwrapped a line in the commit message, so it's a v4.

How is this going to find its way to Linus? I can move this through
the i2c-mux tree, but I obviously need a tag for patch 1/2 for that...

Cheers,
Peter

Changes since v3    https://lkml.org/lkml/2018/5/24/994
- Added Tested-by tags from John.
- Unwrapped commit message for patch 2/2.

Changes since v2    https://lkml.org/lkml/2018/5/24/176
- EXPORT_SYMBOL_GPL(rt_mutex_lock_nested) is more appropriate (the
  rt_ prefix was missing).

Changes since v1    https://lkml.org/lkml/2018/5/24/93
- Further compile tests indicated a missing #define for rt_mutex_lock
  with lockdep enabled, so that one is added.
- I have verified that I don't get any lockdep splat for a local i2c-mux
  setup with these patches applied, and that I do without them.

Cheers,
Peter

Peter Rosin (2):
  rtmutex: allow specifying a subclass for nested locking
  i2c: mux: annotate the nested rt_mutex usage

 drivers/i2c/i2c-core-base.c |  2 +-
 drivers/i2c/i2c-mux.c       |  4 ++--
 include/linux/rtmutex.h     |  7 +++++++
 kernel/locking/rtmutex.c    | 29 +++++++++++++++++++++++++----
 4 files changed, 35 insertions(+), 7 deletions(-)

-- 
2.11.0

[PATCH v4 1/2] rtmutex: allow specifying a subclass for nested locking

[Peter Rosin]

Needed for annotating rt_mutex locks.

Tested-by: John Sperbeck <jsperbeck@google.com>
Signed-off-by: Peter Rosin <peda@axentia.se>
---
 include/linux/rtmutex.h  |  7 +++++++
 kernel/locking/rtmutex.c | 29 +++++++++++++++++++++++++----
 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/include/linux/rtmutex.h b/include/linux/rtmutex.h
index 1b92a28dd672..6fd615a0eea9 100644
--- a/include/linux/rtmutex.h
+++ b/include/linux/rtmutex.h
@@ -106,7 +106,14 @@ static inline int rt_mutex_is_locked(struct rt_mutex *lock)
 extern void __rt_mutex_init(struct rt_mutex *lock, const char *name, struct lock_class_key *key);
 extern void rt_mutex_destroy(struct rt_mutex *lock);
 
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+extern void rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int subclass);
+#define rt_mutex_lock(lock) rt_mutex_lock_nested(lock, 0)
+#else
 extern void rt_mutex_lock(struct rt_mutex *lock);
+#define rt_mutex_lock_nested(lock, subclass) rt_mutex_lock(lock)
+#endif
+
 extern int rt_mutex_lock_interruptible(struct rt_mutex *lock);
 extern int rt_mutex_timed_lock(struct rt_mutex *lock,
 			       struct hrtimer_sleeper *timeout);
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 4f014be7a4b8..2823d4163a37 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1465,6 +1465,29 @@ rt_mutex_fastunlock(struct rt_mutex *lock,
 		rt_mutex_postunlock(&wake_q);
 }
 
+static inline void __rt_mutex_lock(struct rt_mutex *lock, unsigned int subclass)
+{
+	might_sleep();
+
+	mutex_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
+	rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, rt_mutex_slowlock);
+}
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+/**
+ * rt_mutex_lock_nested - lock a rt_mutex
+ *
+ * @lock: the rt_mutex to be locked
+ * @subclass: the lockdep subclass
+ */
+void __sched rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int subclass)
+{
+	__rt_mutex_lock(lock, subclass);
+}
+EXPORT_SYMBOL_GPL(rt_mutex_lock_nested);
+#endif
+
+#ifndef CONFIG_DEBUG_LOCK_ALLOC
 /**
  * rt_mutex_lock - lock a rt_mutex
  *
@@ -1472,12 +1495,10 @@ rt_mutex_fastunlock(struct rt_mutex *lock,
  */
 void __sched rt_mutex_lock(struct rt_mutex *lock)
 {
-	might_sleep();
-
-	mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
-	rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, rt_mutex_slowlock);
+	__rt_mutex_lock(lock, 0);
 }
 EXPORT_SYMBOL_GPL(rt_mutex_lock);
+#endif
 
 /**
  * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
-- 
2.11.0

[PATCH v4 2/2] i2c: mux: annotate the nested rt_mutex usage

[Peter Rosin]

If an i2c topology has instances of nested muxes, then a lockdep splat
is produced when when i2c_parent_lock_bus() is called.  Here is an
example:

============================================
WARNING: possible recursive locking detected
--------------------------------------------
insmod/68159 is trying to acquire lock:
  (i2c_register_adapter#2){+.+.}, at: i2c_parent_lock_bus+0x32/0x50 [i2c_mux]

but task is already holding lock:
  (i2c_register_adapter#2){+.+.}, at: i2c_parent_lock_bus+0x32/0x50 [i2c_mux]

other info that might help us debug this:
  Possible unsafe locking scenario:

        CPU0
        ----
   lock(i2c_register_adapter#2);
   lock(i2c_register_adapter#2);

  *** DEADLOCK ***

  May be due to missing lock nesting notation

1 lock held by insmod/68159:
  #0:  (i2c_register_adapter#2){+.+.}, at: i2c_parent_lock_bus+0x32/0x50 [i2c_mux]

stack backtrace:
CPU: 13 PID: 68159 Comm: insmod Tainted: G           O
Call Trace:
  dump_stack+0x67/0x98
  __lock_acquire+0x162e/0x1780
  lock_acquire+0xba/0x200
  rt_mutex_lock+0x44/0x60
  i2c_parent_lock_bus+0x32/0x50 [i2c_mux]
  i2c_parent_lock_bus+0x3e/0x50 [i2c_mux]
  i2c_smbus_xfer+0xf0/0x700
  i2c_smbus_read_byte+0x42/0x70
  my2c_init+0xa2/0x1000 [my2c]
  do_one_initcall+0x51/0x192
  do_init_module+0x62/0x216
  load_module+0x20f9/0x2b50
  SYSC_init_module+0x19a/0x1c0
  SyS_init_module+0xe/0x10
  do_syscall_64+0x6c/0x1a0
  entry_SYSCALL_64_after_hwframe+0x42/0xb7

Reported-by: John Sperbeck <jsperbeck@google.com>
Tested-by: John Sperbeck <jsperbeck@google.com>
Signed-off-by: Peter Rosin <peda@axentia.se>
---
 drivers/i2c/i2c-core-base.c | 2 +-
 drivers/i2c/i2c-mux.c       | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index f5ec6ec6776f..1157a64c7be3 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -615,7 +615,7 @@ static int i2c_check_addr_busy(struct i2c_adapter *adapter, int addr)
 static void i2c_adapter_lock_bus(struct i2c_adapter *adapter,
 				 unsigned int flags)
 {
-	rt_mutex_lock(&adapter->bus_lock);
+	rt_mutex_lock_nested(&adapter->bus_lock, i2c_adapter_depth(adapter));
 }
 
 /**
diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
index 9669ca4937b8..7ba31f6bf148 100644
--- a/drivers/i2c/i2c-mux.c
+++ b/drivers/i2c/i2c-mux.c
@@ -144,7 +144,7 @@ static void i2c_mux_lock_bus(struct i2c_adapter *adapter, unsigned int flags)
 	struct i2c_mux_priv *priv = adapter->algo_data;
 	struct i2c_adapter *parent = priv->muxc->parent;
 
-	rt_mutex_lock(&parent->mux_lock);
+	rt_mutex_lock_nested(&parent->mux_lock, i2c_adapter_depth(adapter));
 	if (!(flags & I2C_LOCK_ROOT_ADAPTER))
 		return;
 	i2c_lock_bus(parent, flags);
@@ -181,7 +181,7 @@ static void i2c_parent_lock_bus(struct i2c_adapter *adapter,
 	struct i2c_mux_priv *priv = adapter->algo_data;
 	struct i2c_adapter *parent = priv->muxc->parent;
 
-	rt_mutex_lock(&parent->mux_lock);
+	rt_mutex_lock_nested(&parent->mux_lock, i2c_adapter_depth(adapter));
 	i2c_lock_bus(parent, flags);
 }
 
-- 
2.11.0

Re: [PATCH v4 1/2] rtmutex: allow specifying a subclass for nested locking

[Steven Rostedt]

I just noticed this patch because it conflicted with the PREEMPT_RT v4.14
patch.

On Fri, Jul 20, 2018 at 10:39:13AM +0200, Peter Rosin wrote:
> Needed for annotating rt_mutex locks.
> 
> Tested-by: John Sperbeck <jsperbeck@google.com>
> Signed-off-by: Peter Rosin <peda@axentia.se>
> ---
>  include/linux/rtmutex.h  |  7 +++++++
>  kernel/locking/rtmutex.c | 29 +++++++++++++++++++++++++----
>  2 files changed, 32 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/rtmutex.h b/include/linux/rtmutex.h
> index 1b92a28dd672..6fd615a0eea9 100644
> --- a/include/linux/rtmutex.h
> +++ b/include/linux/rtmutex.h
> @@ -106,7 +106,14 @@ static inline int rt_mutex_is_locked(struct rt_mutex *lock)
>  extern void __rt_mutex_init(struct rt_mutex *lock, const char *name, struct lock_class_key *key);
>  extern void rt_mutex_destroy(struct rt_mutex *lock);
>  
> +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> +extern void rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int subclass);
> +#define rt_mutex_lock(lock) rt_mutex_lock_nested(lock, 0)
> +#else
>  extern void rt_mutex_lock(struct rt_mutex *lock);
> +#define rt_mutex_lock_nested(lock, subclass) rt_mutex_lock(lock)
> +#endif
> +
>  extern int rt_mutex_lock_interruptible(struct rt_mutex *lock);
>  extern int rt_mutex_timed_lock(struct rt_mutex *lock,
>  			       struct hrtimer_sleeper *timeout);
> diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
> index 4f014be7a4b8..2823d4163a37 100644
> --- a/kernel/locking/rtmutex.c
> +++ b/kernel/locking/rtmutex.c
> @@ -1465,6 +1465,29 @@ rt_mutex_fastunlock(struct rt_mutex *lock,
>  		rt_mutex_postunlock(&wake_q);
>  }
>  
> +static inline void __rt_mutex_lock(struct rt_mutex *lock, unsigned int subclass)
> +{
> +	might_sleep();
> +
> +	mutex_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
> +	rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, rt_mutex_slowlock);
> +}
> +
> +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> +/**
> + * rt_mutex_lock_nested - lock a rt_mutex
> + *
> + * @lock: the rt_mutex to be locked
> + * @subclass: the lockdep subclass
> + */
> +void __sched rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int subclass)
> +{
> +	__rt_mutex_lock(lock, subclass);
> +}
> +EXPORT_SYMBOL_GPL(rt_mutex_lock_nested);


> +#endif
> +
> +#ifndef CONFIG_DEBUG_LOCK_ALLOC

Why this:

#ifdef CONFIG_DEBUG_LOCK_ALLOC
[..]
#endif

#ifndef CONFIG_DEBUG_LOCK_ALLOC
[..]
#endif

???

This should use #else.

-- Steve


>  /**
>   * rt_mutex_lock - lock a rt_mutex
>   *
> @@ -1472,12 +1495,10 @@ rt_mutex_fastunlock(struct rt_mutex *lock,
>   */
>  void __sched rt_mutex_lock(struct rt_mutex *lock)
>  {
> -	might_sleep();
> -
> -	mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
> -	rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, rt_mutex_slowlock);
> +	__rt_mutex_lock(lock, 0);
>  }
>  EXPORT_SYMBOL_GPL(rt_mutex_lock);
> +#endif
>  
>  /**
>   * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
> -- 
> 2.11.0

Re: [PATCH v4 1/2] rtmutex: allow specifying a subclass for nested locking

[Peter Rosin]

On 2018-09-11 01:27, Steven Rostedt wrote:
> 
> Why this:
> 
> #ifdef CONFIG_DEBUG_LOCK_ALLOC
> [..]
> #endif
> 
> #ifndef CONFIG_DEBUG_LOCK_ALLOC
> [..]
> #endif
> 
> ???
> 
> This should use #else.

Yes. Water under the bridge...

Cheers,
Peter