The following commit has been merged into the locking/core branch of tip:
Commit-ID: af9f006393b53409be0ca83ae234bef840cdef4a
Gitweb: https://git.kernel.org/tip/af9f006393b53409be0ca83ae234bef840cdef4a
Author: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
AuthorDate: Fri, 08 Sep 2023 18:22:49 +02:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Wed, 20 Sep 2023 09:31:11 +02:00
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@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20230908162254.999499-3-bigeasy@xxxxxxxxxxxxx
---
kernel/locking/rtmutex.c | 21 ++++++++++++++++++++-
kernel/locking/ww_rt_mutex.c | 2 +-
2 files changed, 21 insertions(+), 2 deletions(-)
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 21db0df..bcec053 100644
--- 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 d1473c6..c7196de 100644
--- 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;
|