Merge branch 'vmwgfx-next' of git://people.freedesktop.org/~thomash/linux into drm-next

A patchset worked out together with Peter Zijlstra. Ingo is OK with taking
it through the DRM tree:

This is a small fallout from a work to allow batching WW mutex locks and
unlocks.

Our Wound-Wait mutexes actually don't use the Wound-Wait algorithm but
the Wait-Die algorithm. One could perhaps rename those mutexes tree-wide to
"Wait-Die mutexes" or "Deadlock Avoidance mutexes". Another approach suggested
here is to implement also the "Wound-Wait" algorithm as a per-WW-class
choice, as it has advantages in some cases. See for example

http://www.mathcs.emory.edu/~cheung/Courses/554/Syllabus/8-recv+serial/deadlock-compare.html

Now Wound-Wait is a preemptive algorithm, and the preemption is implemented
using a lazy scheme: If a wounded transaction is about to go to sleep on
a contended WW mutex, we return -EDEADLK. That is sufficient for deadlock
prevention. Since with WW mutexes we also require the aborted transaction to
sleep waiting to lock the WW mutex it was aborted on, this choice also provides
a suitable WW mutex to sleep on. If we were to return -EDEADLK on the first
WW mutex lock after the transaction was wounded whether the WW mutex was
contended or not, the transaction might frequently be restarted without a wait,
which is far from optimal. Note also that with the lazy preemption scheme,
contrary to Wait-Die there will be no rollbacks on lock contention of locks
held by a transaction that has completed its locking sequence.

The modeset locks are then changed from Wait-Die to Wound-Wait since the
typical locking pattern of those locks very well matches the criterion for
a substantial reduction in the number of rollbacks. For reservation objects,
the benefit is more unclear at this point and they remain using Wait-Die.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180703105339.4461-1-thellstrom@vmware.com

1 files changed, 28 insertions, 17 deletions

diff --git a/include/linux/ww_mutex.h b/include/linux/ww_mutex.h
index 39fda195bf78..3af7c0e03be5 100644
--- a/include/linux/ww_mutex.h
+++ b/include/linux/ww_mutex.h
@@ -6,8 +6,10 @@
  *
  *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
  *
- * Wound/wait implementation:
+ * Wait/Die implementation:
  *  Copyright (C) 2013 Canonical Ltd.
+ * Choice of algorithm:
+ *  Copyright (C) 2018 WMWare Inc.
  *
  * This file contains the main data structure and API definitions.
  */
@@ -23,14 +25,17 @@ struct ww_class {
 	struct lock_class_key mutex_key;
 	const char *acquire_name;
 	const char *mutex_name;
+	unsigned int is_wait_die;
 };
 
 struct ww_acquire_ctx {
 	struct task_struct *task;
 	unsigned long stamp;
-	unsigned acquired;
+	unsigned int acquired;
+	unsigned short wounded;
+	unsigned short is_wait_die;
 #ifdef CONFIG_DEBUG_MUTEXES
-	unsigned done_acquire;
+	unsigned int done_acquire;
 	struct ww_class *ww_class;
 	struct ww_mutex *contending_lock;
 #endif
@@ -38,8 +43,8 @@ struct ww_acquire_ctx {
 	struct lockdep_map dep_map;
 #endif
 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
-	unsigned deadlock_inject_interval;
-	unsigned deadlock_inject_countdown;
+	unsigned int deadlock_inject_interval;
+	unsigned int deadlock_inject_countdown;
 #endif
 };
 
@@ -58,17 +63,21 @@ struct ww_mutex {
 # define __WW_CLASS_MUTEX_INITIALIZER(lockname, class)
 #endif
 
-#define __WW_CLASS_INITIALIZER(ww_class) \
+#define __WW_CLASS_INITIALIZER(ww_class, _is_wait_die)	    \
 		{ .stamp = ATOMIC_LONG_INIT(0) \
 		, .acquire_name = #ww_class "_acquire" \
-		, .mutex_name = #ww_class "_mutex" }
+		, .mutex_name = #ww_class "_mutex" \
+		, .is_wait_die = _is_wait_die }
 
 #define __WW_MUTEX_INITIALIZER(lockname, class) \
 		{ .base =  __MUTEX_INITIALIZER(lockname.base) \
 		__WW_CLASS_MUTEX_INITIALIZER(lockname, class) }
 
+#define DEFINE_WD_CLASS(classname) \
+	struct ww_class classname = __WW_CLASS_INITIALIZER(classname, 1)
+
 #define DEFINE_WW_CLASS(classname) \
-	struct ww_class classname = __WW_CLASS_INITIALIZER(classname)
+	struct ww_class classname = __WW_CLASS_INITIALIZER(classname, 0)
 
 #define DEFINE_WW_MUTEX(mutexname, ww_class) \
 	struct ww_mutex mutexname = __WW_MUTEX_INITIALIZER(mutexname, ww_class)
@@ -102,7 +111,7 @@ static inline void ww_mutex_init(struct ww_mutex *lock,
  *
  * Context-based w/w mutex acquiring can be done in any order whatsoever within
  * a given lock class. Deadlocks will be detected and handled with the
- * wait/wound logic.
+ * wait/die logic.
  *
  * Mixing of context-based w/w mutex acquiring and single w/w mutex locking can
  * result in undetected deadlocks and is so forbidden. Mixing different contexts
@@ -123,6 +132,8 @@ static inline void ww_acquire_init(struct ww_acquire_ctx *ctx,
 	ctx->task = current;
 	ctx->stamp = atomic_long_inc_return_relaxed(&ww_class->stamp);
 	ctx->acquired = 0;
+	ctx->wounded = false;
+	ctx->is_wait_die = ww_class->is_wait_die;
 #ifdef CONFIG_DEBUG_MUTEXES
 	ctx->ww_class = ww_class;
 	ctx->done_acquire = 0;
@@ -195,13 +206,13 @@ static inline void ww_acquire_fini(struct ww_acquire_ctx *ctx)
  * Lock the w/w mutex exclusively for this task.
  *
  * Deadlocks within a given w/w class of locks are detected and handled with the
- * wait/wound algorithm. If the lock isn't immediately avaiable this function
+ * wait/die algorithm. If the lock isn't immediately available this function
  * will either sleep until it is (wait case). Or it selects the current context
- * for backing off by returning -EDEADLK (wound case). Trying to acquire the
+ * for backing off by returning -EDEADLK (die case). Trying to acquire the
  * same lock with the same context twice is also detected and signalled by
  * returning -EALREADY. Returns 0 if the mutex was successfully acquired.
  *
- * In the wound case the caller must release all currently held w/w mutexes for
+ * In the die case the caller must release all currently held w/w mutexes for
  * the given context and then wait for this contending lock to be available by
  * calling ww_mutex_lock_slow. Alternatively callers can opt to not acquire this
  * lock and proceed with trying to acquire further w/w mutexes (e.g. when
@@ -226,14 +237,14 @@ extern int /* __must_check */ ww_mutex_lock(struct ww_mutex *lock, struct ww_acq
  * Lock the w/w mutex exclusively for this task.
  *
  * Deadlocks within a given w/w class of locks are detected and handled with the
- * wait/wound algorithm. If the lock isn't immediately avaiable this function
+ * wait/die algorithm. If the lock isn't immediately available this function
  * will either sleep until it is (wait case). Or it selects the current context
- * for backing off by returning -EDEADLK (wound case). Trying to acquire the
+ * for backing off by returning -EDEADLK (die case). Trying to acquire the
  * same lock with the same context twice is also detected and signalled by
  * returning -EALREADY. Returns 0 if the mutex was successfully acquired. If a
  * signal arrives while waiting for the lock then this function returns -EINTR.
  *
- * In the wound case the caller must release all currently held w/w mutexes for
+ * In the die case the caller must release all currently held w/w mutexes for
  * the given context and then wait for this contending lock to be available by
  * calling ww_mutex_lock_slow_interruptible. Alternatively callers can opt to
  * not acquire this lock and proceed with trying to acquire further w/w mutexes
@@ -256,7 +267,7 @@ extern int __must_check ww_mutex_lock_interruptible(struct ww_mutex *lock,
  * @lock: the mutex to be acquired
  * @ctx: w/w acquire context
  *
- * Acquires a w/w mutex with the given context after a wound case. This function
+ * Acquires a w/w mutex with the given context after a die case. This function
  * will sleep until the lock becomes available.
  *
  * The caller must have released all w/w mutexes already acquired with the
@@ -290,7 +301,7 @@ ww_mutex_lock_slow(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
  * @lock: the mutex to be acquired
  * @ctx: w/w acquire context
  *
- * Acquires a w/w mutex with the given context after a wound case. This function
+ * Acquires a w/w mutex with the given context after a die case. This function
  * will sleep until the lock becomes available and returns 0 when the lock has
  * been acquired. If a signal arrives while waiting for the lock then this
  * function returns -EINTR.