[RFC][PATCH 1/2] locking: Introduce __cleanup__ based guards

[Peter Zijlstra <peterz@infradead.org>]

Use __attribute__((__cleanup__(func))) to buid various guards:

 - ptr_guard()
 - void_guard() / void_scope()
 - lock_guard() / lock_scope()
 - double_lock_guard() / double_lock_scope()

Where the _guard thingies are variables with scope-based cleanup and
the _scope thingies are basically do-once for-loops with the same.

The CPP is rather impenetrable -- but I'll attempt to write proper
comments if/when people think this is worth pursuing.

Actual usage in the next patch

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 include/linux/compiler_attributes.h |    2 
 include/linux/irqflags.h            |    7 ++
 include/linux/guards.h          |  118 ++++++++++++++++++++++++++++++++++++
 include/linux/mutex.h               |    5 +
 include/linux/preempt.h             |    4 +
 include/linux/rcupdate.h            |    3 
 include/linux/sched/task.h          |    2 
 include/linux/spinlock.h            |   23 +++++++
 8 files changed, 164 insertions(+)

--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -366,4 +366,6 @@
  */
 #define __fix_address noinline __noclone
 
+#define __cleanup(func)			__attribute__((__cleanup__(func)))
+
 #endif /* __LINUX_COMPILER_ATTRIBUTES_H */
--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -13,6 +13,7 @@
 #define _LINUX_TRACE_IRQFLAGS_H
 
 #include <linux/typecheck.h>
+#include <linux/guards.h>
 #include <asm/irqflags.h>
 #include <asm/percpu.h>
 
@@ -267,4 +268,10 @@ extern void warn_bogus_irq_restore(void)
 
 #define irqs_disabled_flags(flags) raw_irqs_disabled_flags(flags)
 
+DEFINE_VOID_GUARD(irq, local_irq_disable(), local_irq_enable())
+DEFINE_VOID_GUARD(irqsave,
+		  local_irq_save(_G->flags),
+		  local_irq_restore(_G->flags),
+		  unsigned long flags;)
+
 #endif
--- /dev/null
+++ b/include/linux/guards.h
@@ -0,0 +1,118 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_GUARDS_H
+#define __LINUX_GUARDS_H
+
+#include <linux/compiler_attributes.h>
+
+/* Pointer Guard */
+
+#define DEFINE_PTR_GUARD(_type, _Type, _Put)				\
+typedef _Type *ptr_guard_##_type##_t;					\
+static inline void ptr_guard_##_type##_cleanup(_Type **_ptr)		\
+{									\
+	_Type *_G = *_ptr;						\
+	if (_G)								\
+		_Put(_G);						\
+}
+
+#define ptr_guard(_type, _name)						\
+	ptr_guard_##_type##_t _name __cleanup(ptr_guard_##_type##_cleanup)
+
+
+/* Void Guard */
+
+#define DEFINE_VOID_GUARD(_type, _Lock, _Unlock, ...)				\
+typedef struct {								\
+	__VA_ARGS__								\
+} void_guard_##_type##_t;							\
+										\
+static inline void void_guard_##_type##_cleanup(void *_g)			\
+{										\
+	void_guard_##_type##_t *_G __maybe_unused = _g;				\
+	_Unlock;								\
+}										\
+										\
+static inline void_guard_##_type##_t void_guard_##_type##_init(void)		\
+{										\
+	void_guard_##_type##_t _g = { }, *_G __maybe_unused = &_g;		\
+	_Lock;									\
+	return _g;								\
+}
+
+#define void_guard(_type, _name)						\
+	void_guard_##_type##_t _name __cleanup(void_guard_##_type##_cleanup) =	\
+	void_guard_##_type##_init()
+
+#define void_scope(_type)							\
+	for (struct { void_guard_##_type##_t guard; bool done; } _scope		\
+	     __cleanup(void_guard_##_type##_cleanup) =				\
+	     { .guard = void_guard_##_type##_init() }; !_scope.done;		\
+	     _scope.done = true)
+
+
+/* Lock Guard */
+
+#define DEFINE_LOCK_GUARD(_type, _Type, _Lock, _Unlock, ...)			\
+typedef struct {								\
+	_Type *lock;								\
+	__VA_ARGS__								\
+} lock_guard_##_type##_t;							\
+										\
+static inline void lock_guard_##_type##_cleanup(void *_g)			\
+{										\
+	lock_guard_##_type##_t *_G = _g;					\
+	_Unlock;								\
+}										\
+										\
+static inline lock_guard_##_type##_t lock_guard_##_type##_init(_Type *lock)	\
+{										\
+	lock_guard_##_type##_t _g = { .lock = lock }, *_G = &_g;		\
+	_Lock;									\
+	return _g;								\
+}
+
+#define lock_guard(_type, _name, _ptr)						\
+	lock_guard_##_type##_t _name __cleanup(lock_guard_##_type##_cleanup) =	\
+	lock_guard_##_type##_init(_ptr)
+
+#define lock_scope(_type, _ptr)							\
+	for (struct { lock_guard_##_type##_t guard; bool done; } _scope		\
+	     __cleanup(lock_guard_##_type##_cleanup) =				\
+	     { .guard = lock_guard_##_type##_init(_ptr) }; !_scope.done;	\
+	     _scope.done = true)
+
+
+/* Double Lock Guard */
+
+#define DEFINE_DOUBLE_LOCK_GUARD(_type, _Type, _Lock, _Unlock, ...)		\
+typedef struct {								\
+	_Type *lock;								\
+	_Type *lock2;								\
+	__VA_ARGS__								\
+} double_lock_guard_##_type##_t;						\
+										\
+static inline void double_lock_guard_##_type##_cleanup(void *_g) 		\
+{										\
+	double_lock_guard_##_type##_t *_G = _g;					\
+	_Unlock;								\
+}										\
+										\
+static inline double_lock_guard_##_type##_t double_lock_guard_##_type##_init(_Type *lock, _Type *lock2) \
+{										\
+	double_lock_guard_##_type##_t _g = { .lock = lock, .lock2 = lock2 }, *_G = &_g;\
+	_Lock;									\
+	return _g;								\
+}
+
+#define double_lock_guard(_type, _name, _ptr, _ptr2)				\
+	double_lock_guard_##_type##_t _name __cleanup(double_lock_guard_##_type##_cleanup) = \
+	double_lock_guard_##_type##_init(_ptr, _ptr2)
+
+#define double_lock_scope(_type, _ptr, _ptr2)					\
+	for (struct { double_lock_guard_##_type##_t guard; bool done; } _scope	\
+	     __cleanup(double_lock_guard_##_type##_cleanup) =			\
+	     { .guard = double_lock_guard_##_type##_init(_ptr, _ptr2) };	\
+	     !_scope.done; _scope.done = true)
+
+
+#endif /* __LINUX_GUARDS_H */
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -19,6 +19,7 @@
 #include <asm/processor.h>
 #include <linux/osq_lock.h>
 #include <linux/debug_locks.h>
+#include <linux/guards.h>
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 # define __DEP_MAP_MUTEX_INITIALIZER(lockname)			\
@@ -219,4 +220,8 @@ extern void mutex_unlock(struct mutex *l
 
 extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
 
+DEFINE_LOCK_GUARD(mutex, struct mutex,
+		  mutex_lock(_G->lock),
+		  mutex_unlock(_G->lock))
+
 #endif /* __LINUX_MUTEX_H */
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -8,6 +8,7 @@
  */
 
 #include <linux/linkage.h>
+#include <linux/guards.h>
 #include <linux/list.h>
 
 /*
@@ -463,4 +464,7 @@ static __always_inline void preempt_enab
 		preempt_enable();
 }
 
+DEFINE_VOID_GUARD(preempt, preempt_disable(), preempt_enable())
+DEFINE_VOID_GUARD(migrate, migrate_disable(), migrate_enable())
+
 #endif /* __LINUX_PREEMPT_H */
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -27,6 +27,7 @@
 #include <linux/preempt.h>
 #include <linux/bottom_half.h>
 #include <linux/lockdep.h>
+#include <linux/guards.h>
 #include <asm/processor.h>
 #include <linux/cpumask.h>
 #include <linux/context_tracking_irq.h>
@@ -1095,4 +1096,6 @@ rcu_head_after_call_rcu(struct rcu_head
 extern int rcu_expedited;
 extern int rcu_normal;
 
+DEFINE_VOID_GUARD(rcu, rcu_read_lock(), rcu_read_unlock())
+
 #endif /* __LINUX_RCUPDATE_H */
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -126,6 +126,8 @@ static inline void put_task_struct(struc
 		__put_task_struct(t);
 }
 
+DEFINE_PTR_GUARD(put_task, struct task_struct, put_task_struct)
+
 static inline void put_task_struct_many(struct task_struct *t, int nr)
 {
 	if (refcount_sub_and_test(nr, &t->usage))
--- a/include/linux/spinlock.h
+++ b/include/linux/spinlock.h
@@ -61,6 +61,7 @@
 #include <linux/stringify.h>
 #include <linux/bottom_half.h>
 #include <linux/lockdep.h>
+#include <linux/guards.h>
 #include <asm/barrier.h>
 #include <asm/mmiowb.h>
 
@@ -502,5 +503,27 @@ int __alloc_bucket_spinlocks(spinlock_t
 
 void free_bucket_spinlocks(spinlock_t *locks);
 
+DEFINE_LOCK_GUARD(raw, raw_spinlock_t,
+		  raw_spin_lock(_G->lock),
+		  raw_spin_unlock(_G->lock))
+DEFINE_LOCK_GUARD(raw_irq, raw_spinlock_t,
+		  raw_spin_lock_irq(_G->lock),
+		  raw_spin_unlock_irq(_G->lock))
+DEFINE_LOCK_GUARD(raw_irqsave, raw_spinlock_t,
+		  raw_spin_lock_irqsave(_G->lock, _G->flags),
+		  raw_spin_unlock_irqrestore(_G->lock, _G->flags),
+		  unsigned long flags;)
+
+DEFINE_LOCK_GUARD(spin, spinlock_t,
+		  spin_lock(_G->lock),
+		  spin_unlock(_G->lock))
+DEFINE_LOCK_GUARD(spin_irq, spinlock_t,
+		  spin_lock_irq(_G->lock),
+		  spin_unlock_irq(_G->lock))
+DEFINE_LOCK_GUARD(spin_irqsave, spinlock_t,
+		  spin_lock_irqsave(_G->lock, _G->flags),
+		  spin_unlock_irqrestore(_G->lock, _G->flags),
+		  unsigned long flags;)
+
 #undef __LINUX_INSIDE_SPINLOCK_H
 #endif /* __LINUX_SPINLOCK_H */