linux-kernel - Re: [PATCH 00/13] [RFC] Rust support

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Date:   Fri, 16 Apr 2021 13:24:23 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     ojeda@...nel.org
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        rust-for-linux@...r.kernel.org, linux-kbuild@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/13] [RFC] Rust support

On Wed, Apr 14, 2021 at 08:45:51PM +0200, ojeda@...nel.org wrote:
>   - Featureful language: sum types, pattern matching, generics,
>     RAII, lifetimes, shared & exclusive references, modules &
>     visibility, powerful hygienic and procedural macros...

IMO RAII is over-valued, but just in case you care, the below seems to
work just fine. No fancy new language needed, works today. Similarly you
can create refcount_t guards, or with a little more work full blown
smart_ptr crud.

---
diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index e19323521f9c..f03a72dd8cea 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -197,4 +197,22 @@ extern void mutex_unlock(struct mutex *lock);
 
 extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
 
+struct mutex_guard {
+	struct mutex *mutex;
+};
+
+static inline struct mutex_guard mutex_guard_lock(struct mutex *mutex)
+{
+	mutex_lock(mutex);
+	return (struct mutex_guard){ .mutex = mutex, };
+}
+
+static inline void mutex_guard_unlock(struct mutex_guard *guard)
+{
+	mutex_unlock(guard->mutex);
+}
+
+#define DEFINE_MUTEX_GUARD(name, lock)			\
+	struct mutex_guard __attribute__((__cleanup__(mutex_guard_unlock))) name = mutex_guard_lock(lock)
+
 #endif /* __LINUX_MUTEX_H */
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 8ee3249de2f0..603d197a83b8 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5715,16 +5715,15 @@ static long perf_compat_ioctl(struct file *file, unsigned int cmd,
 
 int perf_event_task_enable(void)
 {
+	DEFINE_MUTEX_GUARD(event_mutex, &current->perf_event_mutex);
 	struct perf_event_context *ctx;
 	struct perf_event *event;
 
-	mutex_lock(&current->perf_event_mutex);
 	list_for_each_entry(event, &current->perf_event_list, owner_entry) {
 		ctx = perf_event_ctx_lock(event);
 		perf_event_for_each_child(event, _perf_event_enable);
 		perf_event_ctx_unlock(event, ctx);
 	}
-	mutex_unlock(&current->perf_event_mutex);
 
 	return 0;
 }