1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _LINUX_CLEANUP_H
3#define _LINUX_CLEANUP_H
4
5#include <linux/compiler.h>
6#include <linux/err.h>
7#include <linux/args.h>
8
9/**
10 * DOC: scope-based cleanup helpers
11 *
12 * The "goto error" pattern is notorious for introducing subtle resource
13 * leaks. It is tedious and error prone to add new resource acquisition
14 * constraints into code paths that already have several unwind
15 * conditions. The "cleanup" helpers enable the compiler to help with
16 * this tedium and can aid in maintaining LIFO (last in first out)
17 * unwind ordering to avoid unintentional leaks.
18 *
19 * As drivers make up the majority of the kernel code base, here is an
20 * example of using these helpers to clean up PCI drivers. The target of
21 * the cleanups are occasions where a goto is used to unwind a device
22 * reference (pci_dev_put()), or unlock the device (pci_dev_unlock())
23 * before returning.
24 *
25 * The DEFINE_FREE() macro can arrange for PCI device references to be
26 * dropped when the associated variable goes out of scope::
27 *
28 * DEFINE_FREE(pci_dev_put, struct pci_dev *, if (_T) pci_dev_put(_T))
29 * ...
30 * struct pci_dev *dev __free(pci_dev_put) =
31 * pci_get_slot(parent, PCI_DEVFN(0, 0));
32 *
33 * The above will automatically call pci_dev_put() if @dev is non-NULL
34 * when @dev goes out of scope (automatic variable scope). If a function
35 * wants to invoke pci_dev_put() on error, but return @dev (i.e. without
36 * freeing it) on success, it can do::
37 *
38 * return no_free_ptr(dev);
39 *
40 * ...or::
41 *
42 * return_ptr(dev);
43 *
44 * The DEFINE_GUARD() macro can arrange for the PCI device lock to be
45 * dropped when the scope where guard() is invoked ends::
46 *
47 * DEFINE_GUARD(pci_dev, struct pci_dev *, pci_dev_lock(_T), pci_dev_unlock(_T))
48 * ...
49 * guard(pci_dev)(dev);
50 *
51 * The lifetime of the lock obtained by the guard() helper follows the
52 * scope of automatic variable declaration. Take the following example::
53 *
54 * func(...)
55 * {
56 * if (...) {
57 * ...
58 * guard(pci_dev)(dev); // pci_dev_lock() invoked here
59 * ...
60 * } // <- implied pci_dev_unlock() triggered here
61 * }
62 *
63 * Observe the lock is held for the remainder of the "if ()" block not
64 * the remainder of "func()".
65 *
66 * The ACQUIRE() macro can be used in all places that guard() can be
67 * used and additionally support conditional locks::
68 *
69 * DEFINE_GUARD_COND(pci_dev, _try, pci_dev_trylock(_T))
70 * ...
71 * ACQUIRE(pci_dev_try, lock)(dev);
72 * rc = ACQUIRE_ERR(pci_dev_try, &lock);
73 * if (rc)
74 * return rc;
75 * // @lock is held
76 *
77 * Now, when a function uses both __free() and guard()/ACQUIRE(), or
78 * multiple instances of __free(), the LIFO order of variable definition
79 * order matters. GCC documentation says:
80 *
81 * "When multiple variables in the same scope have cleanup attributes,
82 * at exit from the scope their associated cleanup functions are run in
83 * reverse order of definition (last defined, first cleanup)."
84 *
85 * When the unwind order matters it requires that variables be defined
86 * mid-function scope rather than at the top of the file. Take the
87 * following example and notice the bug highlighted by "!!"::
88 *
89 * LIST_HEAD(list);
90 * DEFINE_MUTEX(lock);
91 *
92 * struct object {
93 * struct list_head node;
94 * };
95 *
96 * static struct object *alloc_add(void)
97 * {
98 * struct object *obj;
99 *
100 * lockdep_assert_held(&lock);
101 * obj = kzalloc(sizeof(*obj), GFP_KERNEL);
102 * if (obj) {
103 * LIST_HEAD_INIT(&obj->node);
104 * list_add(obj->node, &list):
105 * }
106 * return obj;
107 * }
108 *
109 * static void remove_free(struct object *obj)
110 * {
111 * lockdep_assert_held(&lock);
112 * list_del(&obj->node);
113 * kfree(obj);
114 * }
115 *
116 * DEFINE_FREE(remove_free, struct object *, if (_T) remove_free(_T))
117 * static int init(void)
118 * {
119 * struct object *obj __free(remove_free) = NULL;
120 * int err;
121 *
122 * guard(mutex)(&lock);
123 * obj = alloc_add();
124 *
125 * if (!obj)
126 * return -ENOMEM;
127 *
128 * err = other_init(obj);
129 * if (err)
130 * return err; // remove_free() called without the lock!!
131 *
132 * no_free_ptr(obj);
133 * return 0;
134 * }
135 *
136 * That bug is fixed by changing init() to call guard() and define +
137 * initialize @obj in this order::
138 *
139 * guard(mutex)(&lock);
140 * struct object *obj __free(remove_free) = alloc_add();
141 *
142 * Given that the "__free(...) = NULL" pattern for variables defined at
143 * the top of the function poses this potential interdependency problem
144 * the recommendation is to always define and assign variables in one
145 * statement and not group variable definitions at the top of the
146 * function when __free() is used.
147 *
148 * Lastly, given that the benefit of cleanup helpers is removal of
149 * "goto", and that the "goto" statement can jump between scopes, the
150 * expectation is that usage of "goto" and cleanup helpers is never
151 * mixed in the same function. I.e. for a given routine, convert all
152 * resources that need a "goto" cleanup to scope-based cleanup, or
153 * convert none of them.
154 */
155
156/*
157 * DEFINE_FREE(name, type, free):
158 * simple helper macro that defines the required wrapper for a __free()
159 * based cleanup function. @free is an expression using '_T' to access the
160 * variable. @free should typically include a NULL test before calling a
161 * function, see the example below.
162 *
163 * __free(name):
164 * variable attribute to add a scoped based cleanup to the variable.
165 *
166 * no_free_ptr(var):
167 * like a non-atomic xchg(var, NULL), such that the cleanup function will
168 * be inhibited -- provided it sanely deals with a NULL value.
169 *
170 * NOTE: this has __must_check semantics so that it is harder to accidentally
171 * leak the resource.
172 *
173 * return_ptr(p):
174 * returns p while inhibiting the __free().
175 *
176 * Ex.
177 *
178 * DEFINE_FREE(kfree, void *, if (_T) kfree(_T))
179 *
180 * void *alloc_obj(...)
181 * {
182 * struct obj *p __free(kfree) = kmalloc(...);
183 * if (!p)
184 * return NULL;
185 *
186 * if (!init_obj(p))
187 * return NULL;
188 *
189 * return_ptr(p);
190 * }
191 *
192 * NOTE: the DEFINE_FREE()'s @free expression includes a NULL test even though
193 * kfree() is fine to be called with a NULL value. This is on purpose. This way
194 * the compiler sees the end of our alloc_obj() function as:
195 *
196 * tmp = p;
197 * p = NULL;
198 * if (p)
199 * kfree(p);
200 * return tmp;
201 *
202 * And through the magic of value-propagation and dead-code-elimination, it
203 * eliminates the actual cleanup call and compiles into:
204 *
205 * return p;
206 *
207 * Without the NULL test it turns into a mess and the compiler can't help us.
208 */
209
210#define DEFINE_FREE(_name, _type, _free) \
211 static inline void __free_##_name(void *p) { _type _T = *(_type *)p; _free; }
212
213#define __free(_name) __cleanup(__free_##_name)
214
215#define __get_and_null(p, nullvalue) \
216 ({ \
217 __auto_type __ptr = &(p); \
218 __auto_type __val = *__ptr; \
219 *__ptr = nullvalue; \
220 __val; \
221 })
222
223static inline __must_check
224const volatile void * __must_check_fn(const volatile void *val)
225{ return val; }
226
227#define no_free_ptr(p) \
228 ((typeof(p)) __must_check_fn((__force const volatile void *)__get_and_null(p, NULL)))
229
230#define return_ptr(p) return no_free_ptr(p)
231
232/*
233 * Only for situations where an allocation is handed in to another function
234 * and consumed by that function on success.
235 *
236 * struct foo *f __free(kfree) = kzalloc(sizeof(*f), GFP_KERNEL);
237 *
238 * setup(f);
239 * if (some_condition)
240 * return -EINVAL;
241 * ....
242 * ret = bar(f);
243 * if (!ret)
244 * retain_and_null_ptr(f);
245 * return ret;
246 *
247 * After retain_and_null_ptr(f) the variable f is NULL and cannot be
248 * dereferenced anymore.
249 */
250#define retain_and_null_ptr(p) ((void)__get_and_null(p, NULL))
251
252/*
253 * DEFINE_CLASS(name, type, exit, init, init_args...):
254 * helper to define the destructor and constructor for a type.
255 * @exit is an expression using '_T' -- similar to FREE above.
256 * @init is an expression in @init_args resulting in @type
257 *
258 * EXTEND_CLASS(name, ext, init, init_args...):
259 * extends class @name to @name@ext with the new constructor
260 *
261 * CLASS(name, var)(args...):
262 * declare the variable @var as an instance of the named class
263 *
264 * Ex.
265 *
266 * DEFINE_CLASS(fdget, struct fd, fdput(_T), fdget(fd), int fd)
267 *
268 * CLASS(fdget, f)(fd);
269 * if (fd_empty(f))
270 * return -EBADF;
271 *
272 * // use 'f' without concern
273 */
274
275#define DEFINE_CLASS(_name, _type, _exit, _init, _init_args...) \
276typedef _type class_##_name##_t; \
277static inline void class_##_name##_destructor(_type *p) \
278{ _type _T = *p; _exit; } \
279static inline _type class_##_name##_constructor(_init_args) \
280{ _type t = _init; return t; }
281
282#define EXTEND_CLASS(_name, ext, _init, _init_args...) \
283typedef class_##_name##_t class_##_name##ext##_t; \
284static inline void class_##_name##ext##_destructor(class_##_name##_t *p)\
285{ class_##_name##_destructor(p); } \
286static inline class_##_name##_t class_##_name##ext##_constructor(_init_args) \
287{ class_##_name##_t t = _init; return t; }
288
289#define CLASS(_name, var) \
290 class_##_name##_t var __cleanup(class_##_name##_destructor) = \
291 class_##_name##_constructor
292
293#define scoped_class(_name, var, args) \
294 for (CLASS(_name, var)(args); \
295 __guard_ptr(_name)(&var) || !__is_cond_ptr(_name); \
296 ({ goto _label; })) \
297 if (0) { \
298_label: \
299 break; \
300 } else
301
302/*
303 * DEFINE_GUARD(name, type, lock, unlock):
304 * trivial wrapper around DEFINE_CLASS() above specifically
305 * for locks.
306 *
307 * DEFINE_GUARD_COND(name, ext, condlock)
308 * wrapper around EXTEND_CLASS above to add conditional lock
309 * variants to a base class, eg. mutex_trylock() or
310 * mutex_lock_interruptible().
311 *
312 * guard(name):
313 * an anonymous instance of the (guard) class, not recommended for
314 * conditional locks.
315 *
316 * scoped_guard (name, args...) { }:
317 * similar to CLASS(name, scope)(args), except the variable (with the
318 * explicit name 'scope') is declard in a for-loop such that its scope is
319 * bound to the next (compound) statement.
320 *
321 * for conditional locks the loop body is skipped when the lock is not
322 * acquired.
323 *
324 * scoped_cond_guard (name, fail, args...) { }:
325 * similar to scoped_guard(), except it does fail when the lock
326 * acquire fails.
327 *
328 * Only for conditional locks.
329 *
330 * ACQUIRE(name, var):
331 * a named instance of the (guard) class, suitable for conditional
332 * locks when paired with ACQUIRE_ERR().
333 *
334 * ACQUIRE_ERR(name, &var):
335 * a helper that is effectively a PTR_ERR() conversion of the guard
336 * pointer. Returns 0 when the lock was acquired and a negative
337 * error code otherwise.
338 */
339
340#define __DEFINE_CLASS_IS_CONDITIONAL(_name, _is_cond) \
341static __maybe_unused const bool class_##_name##_is_conditional = _is_cond
342
343#define __GUARD_IS_ERR(_ptr) \
344 ({ \
345 unsigned long _rc = (__force unsigned long)(_ptr); \
346 unlikely((_rc - 1) >= -MAX_ERRNO - 1); \
347 })
348
349#define __DEFINE_GUARD_LOCK_PTR(_name, _exp) \
350 static inline void *class_##_name##_lock_ptr(class_##_name##_t *_T) \
351 { \
352 void *_ptr = (void *)(__force unsigned long)*(_exp); \
353 if (IS_ERR(_ptr)) { \
354 _ptr = NULL; \
355 } \
356 return _ptr; \
357 } \
358 static inline int class_##_name##_lock_err(class_##_name##_t *_T) \
359 { \
360 long _rc = (__force unsigned long)*(_exp); \
361 if (!_rc) { \
362 _rc = -EBUSY; \
363 } \
364 if (!IS_ERR_VALUE(_rc)) { \
365 _rc = 0; \
366 } \
367 return _rc; \
368 }
369
370#define DEFINE_CLASS_IS_GUARD(_name) \
371 __DEFINE_CLASS_IS_CONDITIONAL(_name, false); \
372 __DEFINE_GUARD_LOCK_PTR(_name, _T)
373
374#define DEFINE_CLASS_IS_COND_GUARD(_name) \
375 __DEFINE_CLASS_IS_CONDITIONAL(_name, true); \
376 __DEFINE_GUARD_LOCK_PTR(_name, _T)
377
378#define DEFINE_GUARD(_name, _type, _lock, _unlock) \
379 DEFINE_CLASS(_name, _type, if (!__GUARD_IS_ERR(_T)) { _unlock; }, ({ _lock; _T; }), _type _T); \
380 DEFINE_CLASS_IS_GUARD(_name)
381
382#define DEFINE_GUARD_COND_4(_name, _ext, _lock, _cond) \
383 __DEFINE_CLASS_IS_CONDITIONAL(_name##_ext, true); \
384 EXTEND_CLASS(_name, _ext, \
385 ({ void *_t = _T; int _RET = (_lock); if (_T && !(_cond)) _t = ERR_PTR(_RET); _t; }), \
386 class_##_name##_t _T) \
387 static inline void * class_##_name##_ext##_lock_ptr(class_##_name##_t *_T) \
388 { return class_##_name##_lock_ptr(_T); } \
389 static inline int class_##_name##_ext##_lock_err(class_##_name##_t *_T) \
390 { return class_##_name##_lock_err(_T); }
391
392/*
393 * Default binary condition; success on 'true'.
394 */
395#define DEFINE_GUARD_COND_3(_name, _ext, _lock) \
396 DEFINE_GUARD_COND_4(_name, _ext, _lock, _RET)
397
398#define DEFINE_GUARD_COND(X...) CONCATENATE(DEFINE_GUARD_COND_, COUNT_ARGS(X))(X)
399
400#define guard(_name) \
401 CLASS(_name, __UNIQUE_ID(guard))
402
403#define __guard_ptr(_name) class_##_name##_lock_ptr
404#define __guard_err(_name) class_##_name##_lock_err
405#define __is_cond_ptr(_name) class_##_name##_is_conditional
406
407#define ACQUIRE(_name, _var) CLASS(_name, _var)
408#define ACQUIRE_ERR(_name, _var) __guard_err(_name)(_var)
409
410/*
411 * Helper macro for scoped_guard().
412 *
413 * Note that the "!__is_cond_ptr(_name)" part of the condition ensures that
414 * compiler would be sure that for the unconditional locks the body of the
415 * loop (caller-provided code glued to the else clause) could not be skipped.
416 * It is needed because the other part - "__guard_ptr(_name)(&scope)" - is too
417 * hard to deduce (even if could be proven true for unconditional locks).
418 */
419#define __scoped_guard(_name, _label, args...) \
420 for (CLASS(_name, scope)(args); \
421 __guard_ptr(_name)(&scope) || !__is_cond_ptr(_name); \
422 ({ goto _label; })) \
423 if (0) { \
424_label: \
425 break; \
426 } else
427
428#define scoped_guard(_name, args...) \
429 __scoped_guard(_name, __UNIQUE_ID(label), args)
430
431#define __scoped_cond_guard(_name, _fail, _label, args...) \
432 for (CLASS(_name, scope)(args); true; ({ goto _label; })) \
433 if (!__guard_ptr(_name)(&scope)) { \
434 BUILD_BUG_ON(!__is_cond_ptr(_name)); \
435 _fail; \
436_label: \
437 break; \
438 } else
439
440#define scoped_cond_guard(_name, _fail, args...) \
441 __scoped_cond_guard(_name, _fail, __UNIQUE_ID(label), args)
442
443/*
444 * Additional helper macros for generating lock guards with types, either for
445 * locks that don't have a native type (eg. RCU, preempt) or those that need a
446 * 'fat' pointer (eg. spin_lock_irqsave).
447 *
448 * DEFINE_LOCK_GUARD_0(name, lock, unlock, ...)
449 * DEFINE_LOCK_GUARD_1(name, type, lock, unlock, ...)
450 * DEFINE_LOCK_GUARD_1_COND(name, ext, condlock)
451 *
452 * will result in the following type:
453 *
454 * typedef struct {
455 * type *lock; // 'type := void' for the _0 variant
456 * __VA_ARGS__;
457 * } class_##name##_t;
458 *
459 * As above, both _lock and _unlock are statements, except this time '_T' will
460 * be a pointer to the above struct.
461 */
462
463#define __DEFINE_UNLOCK_GUARD(_name, _type, _unlock, ...) \
464typedef struct { \
465 _type *lock; \
466 __VA_ARGS__; \
467} class_##_name##_t; \
468 \
469static inline void class_##_name##_destructor(class_##_name##_t *_T) \
470{ \
471 if (!__GUARD_IS_ERR(_T->lock)) { _unlock; } \
472} \
473 \
474__DEFINE_GUARD_LOCK_PTR(_name, &_T->lock)
475
476#define __DEFINE_LOCK_GUARD_1(_name, _type, _lock) \
477static inline class_##_name##_t class_##_name##_constructor(_type *l) \
478{ \
479 class_##_name##_t _t = { .lock = l }, *_T = &_t; \
480 _lock; \
481 return _t; \
482}
483
484#define __DEFINE_LOCK_GUARD_0(_name, _lock) \
485static inline class_##_name##_t class_##_name##_constructor(void) \
486{ \
487 class_##_name##_t _t = { .lock = (void*)1 }, \
488 *_T __maybe_unused = &_t; \
489 _lock; \
490 return _t; \
491}
492
493#define DEFINE_LOCK_GUARD_1(_name, _type, _lock, _unlock, ...) \
494__DEFINE_CLASS_IS_CONDITIONAL(_name, false); \
495__DEFINE_UNLOCK_GUARD(_name, _type, _unlock, __VA_ARGS__) \
496__DEFINE_LOCK_GUARD_1(_name, _type, _lock)
497
498#define DEFINE_LOCK_GUARD_0(_name, _lock, _unlock, ...) \
499__DEFINE_CLASS_IS_CONDITIONAL(_name, false); \
500__DEFINE_UNLOCK_GUARD(_name, void, _unlock, __VA_ARGS__) \
501__DEFINE_LOCK_GUARD_0(_name, _lock)
502
503#define DEFINE_LOCK_GUARD_1_COND_4(_name, _ext, _lock, _cond) \
504 __DEFINE_CLASS_IS_CONDITIONAL(_name##_ext, true); \
505 EXTEND_CLASS(_name, _ext, \
506 ({ class_##_name##_t _t = { .lock = l }, *_T = &_t;\
507 int _RET = (_lock); \
508 if (_T->lock && !(_cond)) _T->lock = ERR_PTR(_RET);\
509 _t; }), \
510 typeof_member(class_##_name##_t, lock) l) \
511 static inline void * class_##_name##_ext##_lock_ptr(class_##_name##_t *_T) \
512 { return class_##_name##_lock_ptr(_T); } \
513 static inline int class_##_name##_ext##_lock_err(class_##_name##_t *_T) \
514 { return class_##_name##_lock_err(_T); }
515
516#define DEFINE_LOCK_GUARD_1_COND_3(_name, _ext, _lock) \
517 DEFINE_LOCK_GUARD_1_COND_4(_name, _ext, _lock, _RET)
518
519#define DEFINE_LOCK_GUARD_1_COND(X...) CONCATENATE(DEFINE_LOCK_GUARD_1_COND_, COUNT_ARGS(X))(X)
520
521#endif /* _LINUX_CLEANUP_H */
522