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diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h
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+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_CLEANUP_H
+#define _LINUX_CLEANUP_H
+
+#include <linux/compiler.h>
+
+/**
+ * DOC: scope-based cleanup helpers
+ *
+ * The "goto error" pattern is notorious for introducing subtle resource
+ * leaks. It is tedious and error prone to add new resource acquisition
+ * constraints into code paths that already have several unwind
+ * conditions. The "cleanup" helpers enable the compiler to help with
+ * this tedium and can aid in maintaining LIFO (last in first out)
+ * unwind ordering to avoid unintentional leaks.
+ *
+ * As drivers make up the majority of the kernel code base, here is an
+ * example of using these helpers to clean up PCI drivers. The target of
+ * the cleanups are occasions where a goto is used to unwind a device
+ * reference (pci_dev_put()), or unlock the device (pci_dev_unlock())
+ * before returning.
+ *
+ * The DEFINE_FREE() macro can arrange for PCI device references to be
+ * dropped when the associated variable goes out of scope::
+ *
+ * DEFINE_FREE(pci_dev_put, struct pci_dev *, if (_T) pci_dev_put(_T))
+ * ...
+ * struct pci_dev *dev __free(pci_dev_put) =
+ * pci_get_slot(parent, PCI_DEVFN(0, 0));
+ *
+ * The above will automatically call pci_dev_put() if @dev is non-NULL
+ * when @dev goes out of scope (automatic variable scope). If a function
+ * wants to invoke pci_dev_put() on error, but return @dev (i.e. without
+ * freeing it) on success, it can do::
+ *
+ * return no_free_ptr(dev);
+ *
+ * ...or::
+ *
+ * return_ptr(dev);
+ *
+ * The DEFINE_GUARD() macro can arrange for the PCI device lock to be
+ * dropped when the scope where guard() is invoked ends::
+ *
+ * DEFINE_GUARD(pci_dev, struct pci_dev *, pci_dev_lock(_T), pci_dev_unlock(_T))
+ * ...
+ * guard(pci_dev)(dev);
+ *
+ * The lifetime of the lock obtained by the guard() helper follows the
+ * scope of automatic variable declaration. Take the following example::
+ *
+ * func(...)
+ * {
+ * if (...) {
+ * ...
+ * guard(pci_dev)(dev); // pci_dev_lock() invoked here
+ * ...
+ * } // <- implied pci_dev_unlock() triggered here
+ * }
+ *
+ * Observe the lock is held for the remainder of the "if ()" block not
+ * the remainder of "func()".
+ *
+ * Now, when a function uses both __free() and guard(), or multiple
+ * instances of __free(), the LIFO order of variable definition order
+ * matters. GCC documentation says:
+ *
+ * "When multiple variables in the same scope have cleanup attributes,
+ * at exit from the scope their associated cleanup functions are run in
+ * reverse order of definition (last defined, first cleanup)."
+ *
+ * When the unwind order matters it requires that variables be defined
+ * mid-function scope rather than at the top of the file. Take the
+ * following example and notice the bug highlighted by "!!"::
+ *
+ * LIST_HEAD(list);
+ * DEFINE_MUTEX(lock);
+ *
+ * struct object {
+ * struct list_head node;
+ * };
+ *
+ * static struct object *alloc_add(void)
+ * {
+ * struct object *obj;
+ *
+ * lockdep_assert_held(&lock);
+ * obj = kzalloc(sizeof(*obj), GFP_KERNEL);
+ * if (obj) {
+ * LIST_HEAD_INIT(&obj->node);
+ * list_add(obj->node, &list):
+ * }
+ * return obj;
+ * }
+ *
+ * static void remove_free(struct object *obj)
+ * {
+ * lockdep_assert_held(&lock);
+ * list_del(&obj->node);
+ * kfree(obj);
+ * }
+ *
+ * DEFINE_FREE(remove_free, struct object *, if (_T) remove_free(_T))
+ * static int init(void)
+ * {
+ * struct object *obj __free(remove_free) = NULL;
+ * int err;
+ *
+ * guard(mutex)(&lock);
+ * obj = alloc_add();
+ *
+ * if (!obj)
+ * return -ENOMEM;
+ *
+ * err = other_init(obj);
+ * if (err)
+ * return err; // remove_free() called without the lock!!
+ *
+ * no_free_ptr(obj);
+ * return 0;
+ * }
+ *
+ * That bug is fixed by changing init() to call guard() and define +
+ * initialize @obj in this order::
+ *
+ * guard(mutex)(&lock);
+ * struct object *obj __free(remove_free) = alloc_add();
+ *
+ * Given that the "__free(...) = NULL" pattern for variables defined at
+ * the top of the function poses this potential interdependency problem
+ * the recommendation is to always define and assign variables in one
+ * statement and not group variable definitions at the top of the
+ * function when __free() is used.
+ *
+ * Lastly, given that the benefit of cleanup helpers is removal of
+ * "goto", and that the "goto" statement can jump between scopes, the
+ * expectation is that usage of "goto" and cleanup helpers is never
+ * mixed in the same function. I.e. for a given routine, convert all
+ * resources that need a "goto" cleanup to scope-based cleanup, or
+ * convert none of them.
+ */
+
+/*
+ * DEFINE_FREE(name, type, free):
+ * simple helper macro that defines the required wrapper for a __free()
+ * based cleanup function. @free is an expression using '_T' to access the
+ * variable. @free should typically include a NULL test before calling a
+ * function, see the example below.
+ *
+ * __free(name):
+ * variable attribute to add a scoped based cleanup to the variable.
+ *
+ * no_free_ptr(var):
+ * like a non-atomic xchg(var, NULL), such that the cleanup function will
+ * be inhibited -- provided it sanely deals with a NULL value.
+ *
+ * NOTE: this has __must_check semantics so that it is harder to accidentally
+ * leak the resource.
+ *
+ * return_ptr(p):
+ * returns p while inhibiting the __free().
+ *
+ * Ex.
+ *
+ * DEFINE_FREE(kfree, void *, if (_T) kfree(_T))
+ *
+ * void *alloc_obj(...)
+ * {
+ * struct obj *p __free(kfree) = kmalloc(...);
+ * if (!p)
+ * return NULL;
+ *
+ * if (!init_obj(p))
+ * return NULL;
+ *
+ * return_ptr(p);
+ * }
+ *
+ * NOTE: the DEFINE_FREE()'s @free expression includes a NULL test even though
+ * kfree() is fine to be called with a NULL value. This is on purpose. This way
+ * the compiler sees the end of our alloc_obj() function as:
+ *
+ * tmp = p;
+ * p = NULL;
+ * if (p)
+ * kfree(p);
+ * return tmp;
+ *
+ * And through the magic of value-propagation and dead-code-elimination, it
+ * eliminates the actual cleanup call and compiles into:
+ *
+ * return p;
+ *
+ * Without the NULL test it turns into a mess and the compiler can't help us.
+ */
+
+#define DEFINE_FREE(_name, _type, _free) \
+ static inline void __free_##_name(void *p) { _type _T = *(_type *)p; _free; }
+
+#define __free(_name) __cleanup(__free_##_name)
+
+#define __get_and_null(p, nullvalue) \
+ ({ \
+ __auto_type __ptr = &(p); \
+ __auto_type __val = *__ptr; \
+ *__ptr = nullvalue; \
+ __val; \
+ })
+
+static inline __must_check
+const volatile void * __must_check_fn(const volatile void *val)
+{ return val; }
+
+#define no_free_ptr(p) \
+ ((typeof(p)) __must_check_fn((__force const volatile void *)__get_and_null(p, NULL)))
+
+#define return_ptr(p) return no_free_ptr(p)
+
+/*
+ * Only for situations where an allocation is handed in to another function
+ * and consumed by that function on success.
+ *
+ * struct foo *f __free(kfree) = kzalloc(sizeof(*f), GFP_KERNEL);
+ *
+ * setup(f);
+ * if (some_condition)
+ * return -EINVAL;
+ * ....
+ * ret = bar(f);
+ * if (!ret)
+ * retain_and_null_ptr(f);
+ * return ret;
+ *
+ * After retain_and_null_ptr(f) the variable f is NULL and cannot be
+ * dereferenced anymore.
+ */
+#define retain_and_null_ptr(p) ((void)__get_and_null(p, NULL))
+
+/*
+ * DEFINE_CLASS(name, type, exit, init, init_args...):
+ * helper to define the destructor and constructor for a type.
+ * @exit is an expression using '_T' -- similar to FREE above.
+ * @init is an expression in @init_args resulting in @type
+ *
+ * EXTEND_CLASS(name, ext, init, init_args...):
+ * extends class @name to @name@ext with the new constructor
+ *
+ * CLASS(name, var)(args...):
+ * declare the variable @var as an instance of the named class
+ *
+ * Ex.
+ *
+ * DEFINE_CLASS(fdget, struct fd, fdput(_T), fdget(fd), int fd)
+ *
+ * CLASS(fdget, f)(fd);
+ * if (fd_empty(f))
+ * return -EBADF;
+ *
+ * // use 'f' without concern
+ */
+
+#define DEFINE_CLASS(_name, _type, _exit, _init, _init_args...) \
+typedef _type class_##_name##_t; \
+static inline void class_##_name##_destructor(_type *p) \
+{ _type _T = *p; _exit; } \
+static inline _type class_##_name##_constructor(_init_args) \
+{ _type t = _init; return t; }
+
+#define EXTEND_CLASS(_name, ext, _init, _init_args...) \
+typedef class_##_name##_t class_##_name##ext##_t; \
+static inline void class_##_name##ext##_destructor(class_##_name##_t *p)\
+{ class_##_name##_destructor(p); } \
+static inline class_##_name##_t class_##_name##ext##_constructor(_init_args) \
+{ class_##_name##_t t = _init; return t; }
+
+#define CLASS(_name, var) \
+ class_##_name##_t var __cleanup(class_##_name##_destructor) = \
+ class_##_name##_constructor
+
+
+/*
+ * DEFINE_GUARD(name, type, lock, unlock):
+ * trivial wrapper around DEFINE_CLASS() above specifically
+ * for locks.
+ *
+ * DEFINE_GUARD_COND(name, ext, condlock)
+ * wrapper around EXTEND_CLASS above to add conditional lock
+ * variants to a base class, eg. mutex_trylock() or
+ * mutex_lock_interruptible().
+ *
+ * guard(name):
+ * an anonymous instance of the (guard) class, not recommended for
+ * conditional locks.
+ *
+ * scoped_guard (name, args...) { }:
+ * similar to CLASS(name, scope)(args), except the variable (with the
+ * explicit name 'scope') is declard in a for-loop such that its scope is
+ * bound to the next (compound) statement.
+ *
+ * for conditional locks the loop body is skipped when the lock is not
+ * acquired.
+ *
+ * scoped_cond_guard (name, fail, args...) { }:
+ * similar to scoped_guard(), except it does fail when the lock
+ * acquire fails.
+ *
+ * Only for conditional locks.
+ */
+
+#define __DEFINE_CLASS_IS_CONDITIONAL(_name, _is_cond) \
+static __maybe_unused const bool class_##_name##_is_conditional = _is_cond
+
+#define __DEFINE_GUARD_LOCK_PTR(_name, _exp) \
+ static inline void * class_##_name##_lock_ptr(class_##_name##_t *_T) \
+ { return (void *)(__force unsigned long)*(_exp); }
+
+#define DEFINE_CLASS_IS_GUARD(_name) \
+ __DEFINE_CLASS_IS_CONDITIONAL(_name, false); \
+ __DEFINE_GUARD_LOCK_PTR(_name, _T)
+
+#define DEFINE_CLASS_IS_COND_GUARD(_name) \
+ __DEFINE_CLASS_IS_CONDITIONAL(_name, true); \
+ __DEFINE_GUARD_LOCK_PTR(_name, _T)
+
+#define DEFINE_GUARD(_name, _type, _lock, _unlock) \
+ DEFINE_CLASS(_name, _type, if (_T) { _unlock; }, ({ _lock; _T; }), _type _T); \
+ DEFINE_CLASS_IS_GUARD(_name)
+
+#define DEFINE_GUARD_COND(_name, _ext, _condlock) \
+ __DEFINE_CLASS_IS_CONDITIONAL(_name##_ext, true); \
+ EXTEND_CLASS(_name, _ext, \
+ ({ void *_t = _T; if (_T && !(_condlock)) _t = NULL; _t; }), \
+ class_##_name##_t _T) \
+ static inline void * class_##_name##_ext##_lock_ptr(class_##_name##_t *_T) \
+ { return class_##_name##_lock_ptr(_T); }
+
+#define guard(_name) \
+ CLASS(_name, __UNIQUE_ID(guard))
+
+#define __guard_ptr(_name) class_##_name##_lock_ptr
+#define __is_cond_ptr(_name) class_##_name##_is_conditional
+
+/*
+ * Helper macro for scoped_guard().
+ *
+ * Note that the "!__is_cond_ptr(_name)" part of the condition ensures that
+ * compiler would be sure that for the unconditional locks the body of the
+ * loop (caller-provided code glued to the else clause) could not be skipped.
+ * It is needed because the other part - "__guard_ptr(_name)(&scope)" - is too
+ * hard to deduce (even if could be proven true for unconditional locks).
+ */
+#define __scoped_guard(_name, _label, args...) \
+ for (CLASS(_name, scope)(args); \
+ __guard_ptr(_name)(&scope) || !__is_cond_ptr(_name); \
+ ({ goto _label; })) \
+ if (0) { \
+_label: \
+ break; \
+ } else
+
+#define scoped_guard(_name, args...) \
+ __scoped_guard(_name, __UNIQUE_ID(label), args)
+
+#define __scoped_cond_guard(_name, _fail, _label, args...) \
+ for (CLASS(_name, scope)(args); true; ({ goto _label; })) \
+ if (!__guard_ptr(_name)(&scope)) { \
+ BUILD_BUG_ON(!__is_cond_ptr(_name)); \
+ _fail; \
+_label: \
+ break; \
+ } else
+
+#define scoped_cond_guard(_name, _fail, args...) \
+ __scoped_cond_guard(_name, _fail, __UNIQUE_ID(label), args)
+
+/*
+ * Additional helper macros for generating lock guards with types, either for
+ * locks that don't have a native type (eg. RCU, preempt) or those that need a
+ * 'fat' pointer (eg. spin_lock_irqsave).
+ *
+ * DEFINE_LOCK_GUARD_0(name, lock, unlock, ...)
+ * DEFINE_LOCK_GUARD_1(name, type, lock, unlock, ...)
+ * DEFINE_LOCK_GUARD_1_COND(name, ext, condlock)
+ *
+ * will result in the following type:
+ *
+ * typedef struct {
+ * type *lock; // 'type := void' for the _0 variant
+ * __VA_ARGS__;
+ * } class_##name##_t;
+ *
+ * As above, both _lock and _unlock are statements, except this time '_T' will
+ * be a pointer to the above struct.
+ */
+
+#define __DEFINE_UNLOCK_GUARD(_name, _type, _unlock, ...) \
+typedef struct { \
+ _type *lock; \
+ __VA_ARGS__; \
+} class_##_name##_t; \
+ \
+static inline void class_##_name##_destructor(class_##_name##_t *_T) \
+{ \
+ if (_T->lock) { _unlock; } \
+} \
+ \
+__DEFINE_GUARD_LOCK_PTR(_name, &_T->lock)
+
+#define __DEFINE_LOCK_GUARD_1(_name, _type, _lock) \
+static inline class_##_name##_t class_##_name##_constructor(_type *l) \
+{ \
+ class_##_name##_t _t = { .lock = l }, *_T = &_t; \
+ _lock; \
+ return _t; \
+}
+
+#define __DEFINE_LOCK_GUARD_0(_name, _lock) \
+static inline class_##_name##_t class_##_name##_constructor(void) \
+{ \
+ class_##_name##_t _t = { .lock = (void*)1 }, \
+ *_T __maybe_unused = &_t; \
+ _lock; \
+ return _t; \
+}
+
+#define DEFINE_LOCK_GUARD_1(_name, _type, _lock, _unlock, ...) \
+__DEFINE_CLASS_IS_CONDITIONAL(_name, false); \
+__DEFINE_UNLOCK_GUARD(_name, _type, _unlock, __VA_ARGS__) \
+__DEFINE_LOCK_GUARD_1(_name, _type, _lock)
+
+#define DEFINE_LOCK_GUARD_0(_name, _lock, _unlock, ...) \
+__DEFINE_CLASS_IS_CONDITIONAL(_name, false); \
+__DEFINE_UNLOCK_GUARD(_name, void, _unlock, __VA_ARGS__) \
+__DEFINE_LOCK_GUARD_0(_name, _lock)
+
+#define DEFINE_LOCK_GUARD_1_COND(_name, _ext, _condlock) \
+ __DEFINE_CLASS_IS_CONDITIONAL(_name##_ext, true); \
+ EXTEND_CLASS(_name, _ext, \
+ ({ class_##_name##_t _t = { .lock = l }, *_T = &_t;\
+ if (_T->lock && !(_condlock)) _T->lock = NULL; \
+ _t; }), \
+ typeof_member(class_##_name##_t, lock) l) \
+ static inline void * class_##_name##_ext##_lock_ptr(class_##_name##_t *_T) \
+ { return class_##_name##_lock_ptr(_T); }
+
+
+#endif /* _LINUX_CLEANUP_H */
Copyright © 1996 – 2023 Jason A. Donenfeld. All Rights Reverse Engineered.