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Message-ID: <YTtznr85mg5xXouP@hirez.programming.kicks-ass.net>
Date: Fri, 10 Sep 2021 17:02:54 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
Cc: intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
Waiman Long <longman@...hat.com>,
Boqun Feng <boqun.feng@...il.com>,
Liam Girdwood <lgirdwood@...il.com>,
Mark Brown <broonie@...nel.org>, linux-kernel@...r.kernel.org,
Daniel Vetter <daniel.vetter@...ll.ch>
Subject: Re: [PATCH v2] kernel/locking: Add context to ww_mutex_trylock.
On Thu, Sep 09, 2021 at 11:32:18AM +0200, Maarten Lankhorst wrote:
> diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
> index d456579d0952..791c28005eef 100644
> --- a/kernel/locking/mutex.c
> +++ b/kernel/locking/mutex.c
> @@ -736,6 +736,44 @@ __ww_mutex_lock(struct mutex *lock, unsigned int state, unsigned int subclass,
> return __mutex_lock_common(lock, state, subclass, NULL, ip, ww_ctx, true);
> }
>
> +/**
> + * ww_mutex_trylock - tries to acquire the w/w mutex with optional acquire context
> + * @lock: mutex to lock
> + * @ctx: optional w/w acquire context
> + *
> + * Trylocks a mutex with the optional acquire context; no deadlock detection is
> + * possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise.
> + *
> + * Unlike ww_mutex_lock, no deadlock handling is performed. However, if a @ctx is
> + * specified, -EALREADY and -EDEADLK handling may happen in calls to ww_mutex_lock.
> + *
> + * A mutex acquired with this function must be released with ww_mutex_unlock.
> + */
> +int __sched
> +ww_mutex_trylock(struct ww_mutex *ww, struct ww_acquire_ctx *ctx)
> +{
> + bool locked;
> +
> + if (!ctx)
> + return mutex_trylock(&ww->base);
> +
> +#ifdef CONFIG_DEBUG_MUTEXES
> + DEBUG_LOCKS_WARN_ON(ww->base.magic != &ww->base);
> +#endif
> +
> + preempt_disable();
> + locked = __mutex_trylock(&ww->base);
> +
> + if (locked) {
> + ww_mutex_set_context_fastpath(ww, ctx);
> + mutex_acquire_nest(&ww->base.dep_map, 0, 1, &ctx->dep_map, _RET_IP_);
> + }
> + preempt_enable();
> +
> + return locked;
> +}
> +EXPORT_SYMBOL(ww_mutex_trylock);
> +
> #ifdef CONFIG_DEBUG_LOCK_ALLOC
> void __sched
> mutex_lock_nested(struct mutex *lock, unsigned int subclass)
> diff --git a/kernel/locking/ww_rt_mutex.c b/kernel/locking/ww_rt_mutex.c
> index 3f1fff7d2780..c4cb863edb4c 100644
> --- a/kernel/locking/ww_rt_mutex.c
> +++ b/kernel/locking/ww_rt_mutex.c
> @@ -50,6 +50,18 @@ __ww_rt_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ww_ctx,
> return ret;
> }
>
> +int __sched
> +ww_mutex_trylock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
> +{
> + int locked = rt_mutex_trylock(&lock->base);
> +
> + if (locked && ctx)
> + ww_mutex_set_context_fastpath(lock, ctx);
> +
> + return locked;
> +}
> +EXPORT_SYMBOL(ww_mutex_trylock);
> +
> int __sched
> ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
> {
That doesn't look right, how's this for you?
---
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -94,6 +94,9 @@ static inline unsigned long __owner_flag
return owner & MUTEX_FLAGS;
}
+/*
+ * Returns: __mutex_owner(lock) on failure or NULL on success.
+ */
static inline struct task_struct *__mutex_trylock_common(struct mutex *lock, bool handoff)
{
unsigned long owner, curr = (unsigned long)current;
@@ -736,6 +739,47 @@ __ww_mutex_lock(struct mutex *lock, unsi
return __mutex_lock_common(lock, state, subclass, NULL, ip, ww_ctx, true);
}
+/**
+ * ww_mutex_trylock - tries to acquire the w/w mutex with optional acquire context
+ * @ww: mutex to lock
+ * @ww_ctx: optional w/w acquire context
+ *
+ * Trylocks a mutex with the optional acquire context; no deadlock detection is
+ * possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise.
+ *
+ * Unlike ww_mutex_lock, no deadlock handling is performed. However, if a @ctx is
+ * specified, -EALREADY handling may happen in calls to ww_mutex_trylock.
+ *
+ * A mutex acquired with this function must be released with ww_mutex_unlock.
+ */
+int ww_mutex_trylock(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx)
+{
+ if (!ww_ctx)
+ return mutex_trylock(&ww->base);
+
+ MUTEX_WARN_ON(ww->base.magic != &ww->base);
+
+ if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
+ return -EALREADY;
+
+ /*
+ * Reset the wounded flag after a kill. No other process can
+ * race and wound us here, since they can't have a valid owner
+ * pointer if we don't have any locks held.
+ */
+ if (ww_ctx->acquired == 0)
+ ww_ctx->wounded = 0;
+
+ if (__mutex_trylock(&ww->base)) {
+ ww_mutex_set_context_fastpath(ww, ww_ctx);
+ mutex_acquire_nest(&ww->base.dep_map, 0, 1, &ww_ctx->dep_map, _RET_IP_);
+ return 1;
+ }
+
+ return 0;
+}
+EXPORT_SYMBOL(ww_mutex_trylock);
+
#ifdef CONFIG_DEBUG_LOCK_ALLOC
void __sched
mutex_lock_nested(struct mutex *lock, unsigned int subclass)
--- a/kernel/locking/ww_rt_mutex.c
+++ b/kernel/locking/ww_rt_mutex.c
@@ -9,6 +9,34 @@
#define WW_RT
#include "rtmutex.c"
+int ww_mutex_trylock(struct ww_mutex *lock, struct ww_acquire_ctx *ww_ctx)
+{
+ struct rt_mutex *rtm = &lock->base;
+
+ if (!ww_ctx)
+ return rt_mutex_trylock(rtm);
+
+ if (unlikely(ww_ctx == READ_ONCE(lock->ctx)))
+ return -EALREADY;
+
+ /*
+ * Reset the wounded flag after a kill. No other process can
+ * race and wound us here, since they can't have a valid owner
+ * pointer if we don't have any locks held.
+ */
+ if (ww_ctx->acquired == 0)
+ ww_ctx->wounded = 0;
+
+ if (__rt_mutex_trylock(&rtm->rtmutex)) {
+ ww_mutex_set_context_fastpath(lock, ww_ctx);
+ mutex_acquire_nest(&rtm->dep_map, 0, 1, ww_ctx->dep_map, _RET_IP_);
+ return 1;
+ }
+
+ return 0;
+}
+EXPORT_SYMBOL(ww_mutex_trylock);
+
static int __sched
__ww_rt_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ww_ctx,
unsigned int state, unsigned long ip)
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