locking/ww_mutex: Set use_ww_ctx even when locking without a context

We will add a new field to struct mutex_waiter.  This field must be
initialized for all waiters if any waiter uses the ww_use_ctx path.

So there is a trade-off: Keep ww_mutex locking without a context on
the faster non-use_ww_ctx path, at the cost of adding the
initialization to all mutex locks (including non-ww_mutexes), or avoid
the additional cost for non-ww_mutex locks, at the cost of adding
additional checks to the use_ww_ctx path.

We take the latter choice.  It may be worth eliminating the users of
ww_mutex_lock(lock, NULL), but there are a lot of them.

Signed-off-by: Nicolai Hähnle <Nicolai.Haehnle@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Maarten Lankhorst <dev@mblankhorst.nl>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dri-devel@lists.freedesktop.org
Link: http://lkml.kernel.org/r/1482346000-9927-5-git-send-email-nhaehnle@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/include/linux/ww_mutex.h b/include/linux/ww_mutex.h
index 7b00668..5f2e837 100644 (file)
--- a/include/linux/ww_mutex.h
+++ b/include/linux/ww_mutex.h
@@ -222,11 +222,7 @@ extern int __must_check __ww_mutex_lock_interruptible(struct ww_mutex *lock,
  */
 static inline int ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 {
-       if (ctx)
-               return __ww_mutex_lock(lock, ctx);
-
-       mutex_lock(&lock->base);
-       return 0;
+       return __ww_mutex_lock(lock, ctx);
 }
 
 /**
@@ -262,10 +258,7 @@ static inline int ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ct
 static inline int __must_check ww_mutex_lock_interruptible(struct ww_mutex *lock,
                                                           struct ww_acquire_ctx *ctx)
 {
-       if (ctx)
-               return __ww_mutex_lock_interruptible(lock, ctx);
-       else
-               return mutex_lock_interruptible(&lock->base);
+       return __ww_mutex_lock_interruptible(lock, ctx);
 }
 
 /**

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 9ad03b9..44a64c0 100644 (file)
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -469,7 +469,7 @@ static bool mutex_optimistic_spin(struct mutex *lock,
        for (;;) {
                struct task_struct *owner;
 
-               if (use_ww_ctx && ww_ctx->acquired > 0) {
+               if (use_ww_ctx && ww_ctx && ww_ctx->acquired > 0) {
                        struct ww_mutex *ww;
 
                        ww = container_of(lock, struct ww_mutex, base);
@@ -629,8 +629,9 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
        struct ww_mutex *ww;
        int ret;
 
-       if (use_ww_ctx) {
-               ww = container_of(lock, struct ww_mutex, base);
+       ww = container_of(lock, struct ww_mutex, base);
+
+       if (use_ww_ctx && ww_ctx) {
                if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
                        return -EALREADY;
        }
@@ -642,7 +643,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
            mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, false)) {
                /* got the lock, yay! */
                lock_acquired(&lock->dep_map, ip);
-               if (use_ww_ctx)
+               if (use_ww_ctx && ww_ctx)
                        ww_mutex_set_context_fastpath(ww, ww_ctx);
                preempt_enable();
                return 0;
@@ -688,7 +689,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
                        goto err;
                }
 
-               if (use_ww_ctx && ww_ctx->acquired > 0) {
+               if (use_ww_ctx && ww_ctx && ww_ctx->acquired > 0) {
                        ret = __ww_mutex_lock_check_stamp(lock, ww_ctx);
                        if (ret)
                                goto err;
@@ -728,7 +729,7 @@ skip_wait:
        /* got the lock - cleanup and rejoice! */
        lock_acquired(&lock->dep_map, ip);
 
-       if (use_ww_ctx)
+       if (use_ww_ctx && ww_ctx)
                ww_mutex_set_context_slowpath(ww, ww_ctx);
 
        spin_unlock_mutex(&lock->wait_lock, flags);
@@ -816,8 +817,9 @@ __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 
        might_sleep();
        ret =  __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE,
-                                  0, &ctx->dep_map, _RET_IP_, ctx, 1);
-       if (!ret && ctx->acquired > 1)
+                                  0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
+                                  ctx, 1);
+       if (!ret && ctx && ctx->acquired > 1)
                return ww_mutex_deadlock_injection(lock, ctx);
 
        return ret;
@@ -831,9 +833,10 @@ __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 
        might_sleep();
        ret = __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE,
-                                 0, &ctx->dep_map, _RET_IP_, ctx, 1);
+                                 0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
+                                 ctx, 1);
 
-       if (!ret && ctx->acquired > 1)
+       if (!ret && ctx && ctx->acquired > 1)
                return ww_mutex_deadlock_injection(lock, ctx);
 
        return ret;
@@ -1021,7 +1024,8 @@ __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
        might_sleep();
 
        if (__mutex_trylock_fast(&lock->base)) {
-               ww_mutex_set_context_fastpath(lock, ctx);
+               if (ctx)
+                       ww_mutex_set_context_fastpath(lock, ctx);
                return 0;
        }
 
@@ -1035,7 +1039,8 @@ __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
        might_sleep();
 
        if (__mutex_trylock_fast(&lock->base)) {
-               ww_mutex_set_context_fastpath(lock, ctx);
+               if (ctx)
+                       ww_mutex_set_context_fastpath(lock, ctx);
                return 0;
        }