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

[Chris Wilson <chris@chris-wilson.co.uk>]

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@chris-wilson.co.uk>
Cc: Ben Widawsky <benjamin.widawsky@intel.com>
---
 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)
 
 #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