locking/rtmutex: Avoid unconditional slowpath for DEBUG_RT_MUTEXES

With DEBUG_RT_MUTEXES enabled the fast-path rt_mutex_cmpxchg_acquire()
always fails and all lock operations take the slow path.

Provide a new helper inline rt_mutex_try_acquire() which maps to
rt_mutex_cmpxchg_acquire() in the non-debug case. For the debug case
it invokes rt_mutex_slowtrylock() which can acquire a non-contended
rtmutex under full debug coverage.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20230908162254.999499-3-bigeasy@linutronix.de

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 21db0df0eb00070f4b96ff74dd27754a5807e9ae..bcec0533a0cc09296fbce6cd9e5a7b9ea89b0f32 100644 (file)
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -218,6 +218,11 @@ static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock,
        return try_cmpxchg_acquire(&lock->owner, &old, new);
 }
 
+static __always_inline bool rt_mutex_try_acquire(struct rt_mutex_base *lock)
+{
+       return rt_mutex_cmpxchg_acquire(lock, NULL, current);
+}
+
 static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock,
                                                     struct task_struct *old,
                                                     struct task_struct *new)
@@ -297,6 +302,20 @@ static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock,
 
 }
 
+static int __sched rt_mutex_slowtrylock(struct rt_mutex_base *lock);
+
+static __always_inline bool rt_mutex_try_acquire(struct rt_mutex_base *lock)
+{
+       /*
+        * With debug enabled rt_mutex_cmpxchg trylock() will always fail.
+        *
+        * Avoid unconditionally taking the slow path by using
+        * rt_mutex_slow_trylock() which is covered by the debug code and can
+        * acquire a non-contended rtmutex.
+        */
+       return rt_mutex_slowtrylock(lock);
+}
+
 static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock,
                                                     struct task_struct *old,
                                                     struct task_struct *new)
@@ -1755,7 +1774,7 @@ static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock,
 static __always_inline int __rt_mutex_lock(struct rt_mutex_base *lock,
                                           unsigned int state)
 {
-       if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
+       if (likely(rt_mutex_try_acquire(lock)))
                return 0;
 
        return rt_mutex_slowlock(lock, NULL, state);

diff --git a/kernel/locking/ww_rt_mutex.c b/kernel/locking/ww_rt_mutex.c
index d1473c624105c89f492c1baad1ba9f4f407b2706..c7196de838edcd614abbfcecad7c69e624495005 100644 (file)
--- a/kernel/locking/ww_rt_mutex.c
+++ b/kernel/locking/ww_rt_mutex.c
@@ -62,7 +62,7 @@ __ww_rt_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ww_ctx,
        }
        mutex_acquire_nest(&rtm->dep_map, 0, 0, nest_lock, ip);
 
-       if (likely(rt_mutex_cmpxchg_acquire(&rtm->rtmutex, NULL, current))) {
+       if (likely(rt_mutex_try_acquire(&rtm->rtmutex))) {
                if (ww_ctx)
                        ww_mutex_set_context_fastpath(lock, ww_ctx);
                return 0;