[Intel-gfx] [PATCH] mutex: Export an interface to wrap a mutex lock

[Ben Widawsky]

On Sat, Jul 26, 2014 at 09:01:55AM +0100, Chris Wilson wrote:
> In i915, we have a big mutex around our device struct - every time before
> we attempt to communicate with the GPU, we acquire the mutex. This makes
> it a convenient juncture to place our GPU error handling - before we take
> the mutex we first check whether the GPU is hung or whether we are in
> the process of recovering from a GPU hang. So we wrap the call to
> mutex_lock() alongside our additional error handling routines.
> 
> The downside of using a wrapper around mutex_lock() is that lockdep and
> lockstat cannot discriminate the true callers of mutex_lock(). Unless we
> provide a means for the wrapper to pass that information down.
> 
> It also appears that i915 is unique in this manner of wrapping
> mutex_lock().
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Ben Widawsky <benjamin.widawsky at intel.com>

With the one fix inline, take your pick:

Reported-and-tested-by: Ben Widawsky <ben at bwidawsk.net>
Reviewed-by: Ben Widawsky <ben at bwidawsk.net>

I find it very strange that i915 is unique here. It makes me feel like
we're doin' in wrong. BTW, a cleaned up version of the macro version I
sent you might meet with less resistance given that no other driver
needs it [currently].

Also, looking at this code now, we could probably replace a bunch of
mutex_lock()'s in i915 with mutex_lock_wrapper(..., TASK_KILLABLE, ...)


> ---
>  drivers/gpu/drm/i915/i915_gem.c |  4 +++-
>  include/linux/mutex.h           |  9 +++++++++
>  kernel/locking/mutex.c          | 36 ++++++++++++++++++++++++++++++++++++
>  3 files changed, 48 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index ae3c7b6162f5..888acd01db44 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -233,7 +233,9 @@ int i915_mutex_lock_interruptible(struct drm_device *dev)
>  	if (ret)
>  		return ret;
>  
> -	ret = mutex_lock_interruptible(&dev->struct_mutex);
> +	ret = mutex_lock_wrapper(&dev->struct_mutex,
> +				 TASK_INTERRUPTIBLE,
> +				 _RET_IP_);
>  	if (ret)
>  		return ret;
>  
> diff --git a/include/linux/mutex.h b/include/linux/mutex.h
> index 42aa9b9ecd5f..b88255a390a2 100644
> --- a/include/linux/mutex.h
> +++ b/include/linux/mutex.h
> @@ -143,10 +143,15 @@ extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
>  					unsigned int subclass);
>  extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
>  					unsigned int subclass);
> +extern int __must_check mutex_lock_wrapper_nested(struct mutex *lock,
> +						  unsigned int subclass,
> +						  long state,
> +						  unsigned long ip);
>  
>  #define mutex_lock(lock) mutex_lock_nested(lock, 0)
>  #define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
>  #define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
> +#define mutex_lock_wrapper(lock, state, ip) mutex_lock_killable_nested(lock, 0, state, ip)

s/mutex_lock_killable_nested/mutex_lock_wrapper_nested/

>  
>  #define mutex_lock_nest_lock(lock, nest_lock)				\
>  do {									\
> @@ -158,10 +163,14 @@ do {									\
>  extern void mutex_lock(struct mutex *lock);
>  extern int __must_check mutex_lock_interruptible(struct mutex *lock);
>  extern int __must_check mutex_lock_killable(struct mutex *lock);
> +extern int __must_check mutex_lock_wrapper(struct mutex *lock,
> +					   long state,
> +					   unsigned long ip);
>  
>  # define mutex_lock_nested(lock, subclass) mutex_lock(lock)
>  # define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
>  # define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
> +# define mutex_lock_wrapper_nested(lock, subclass, state, ip) mutex_lock_wrapper(lock, state, ip)
>  # define mutex_lock_nest_lock(lock, nest_lock) mutex_lock(lock)
>  #endif
>  
> diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
> index acca2c1a3c5e..243ee5fc5dc3 100644
> --- a/kernel/locking/mutex.c
> +++ b/kernel/locking/mutex.c
> @@ -619,6 +619,17 @@ mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
>  
>  EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
>  
> +int __sched
> +mutex_lock_wrapper_nested(struct mutex *lock, unsigned int subclass,
> +			  long state, unsigned long ip)
> +{
> +	might_sleep();
> +	return __mutex_lock_common(lock, state,
> +				   subclass, NULL, ip, NULL, 0);
> +}
> +
> +EXPORT_SYMBOL_GPL(mutex_lock_wrapper_nested);
> +
>  static inline int
>  ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
>  {
> @@ -733,6 +744,9 @@ __mutex_lock_killable_slowpath(struct mutex *lock);
>  static noinline int __sched
>  __mutex_lock_interruptible_slowpath(struct mutex *lock);
>  
> +static noinline int __sched
> +__mutex_lock_wrapper_slowpath(struct mutex *lock, long state, unsigned long ip);
> +
>  /**
>   * mutex_lock_interruptible - acquire the mutex, interruptible
>   * @lock: the mutex to be acquired
> @@ -759,6 +773,21 @@ int __sched mutex_lock_interruptible(struct mutex *lock)
>  
>  EXPORT_SYMBOL(mutex_lock_interruptible);
>  
> +int __sched mutex_lock_wrapper(struct mutex *lock, long state, unsigned long ip)
> +{
> +	int ret;
> +
> +	might_sleep();
> +	ret =  __mutex_fastpath_lock_retval(&lock->count);
> +	if (likely(!ret)) {
> +		mutex_set_owner(lock);
> +		return 0;
> +	} else
> +		return __mutex_lock_wrapper_slowpath(lock, state, ip);
> +}
> +
> +EXPORT_SYMBOL(mutex_lock_wrapper);
> +
>  int __sched mutex_lock_killable(struct mutex *lock)
>  {
>  	int ret;
> @@ -797,6 +826,13 @@ __mutex_lock_interruptible_slowpath(struct mutex *lock)
>  }
>  
>  static noinline int __sched
> +__mutex_lock_wrapper_slowpath(struct mutex *lock, long state, unsigned long ip)
> +{
> +	return __mutex_lock_common(lock, state, 0,
> +				   NULL, ip, NULL, 0);
> +}
> +
> +static noinline int __sched
>  __ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
>  {
>  	return __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE, 0,
> -- 
> 2.0.1
> 

-- 
Ben Widawsky, Intel Open Source Technology Center