From: Przemek Kitszel przemyslaw.kitszel@intel.com
[ Upstream commit fcc22ac5baf06dd17193de44b60dbceea6461983 ]
Change scoped_guard() and scoped_cond_guard() macros to make reasoning about them easier for static analysis tools (smatch, compiler diagnostics), especially to enable them to tell if the given usage of scoped_guard() is with a conditional lock class (interruptible-locks, try-locks) or not (like simple mutex_lock()).
Add compile-time error if scoped_cond_guard() is used for non-conditional lock class.
Beyond easier tooling and a little shrink reported by bloat-o-meter this patch enables developer to write code like:
int foo(struct my_drv *adapter) { scoped_guard(spinlock, &adapter->some_spinlock) return adapter->spinlock_protected_var; }
Current scoped_guard() implementation does not support that, due to compiler complaining: error: control reaches end of non-void function [-Werror=return-type]
Technical stuff about the change: scoped_guard() macro uses common idiom of using "for" statement to declare a scoped variable. Unfortunately, current logic is too hard for compiler diagnostics to be sure that there is exactly one loop step; fix that.
To make any loop so trivial that there is no above warning, it must not depend on any non-const variable to tell if there are more steps. There is no obvious solution for that in C, but one could use the compound statement expression with "goto" jumping past the "loop", effectively leaving only the subscope part of the loop semantics.
More impl details: one more level of macro indirection is now needed to avoid duplicating label names; I didn't spot any other place that is using the "for (...; goto label) if (0) label: break;" idiom, so it's not packed for reuse beyond scoped_guard() family, what makes actual macros code cleaner.
There was also a need to introduce const true/false variable per lock class, it is used to aid compiler diagnostics reasoning about "exactly 1 step" loops (note that converting that to function would undo the whole benefit).
Big thanks to Andy Shevchenko for help on this patch, both internal and public, ranging from whitespace/formatting, through commit message clarifications, general improvements, ending with presenting alternative approaches - all despite not even liking the idea.
Big thanks to Dmitry Torokhov for the idea of compile-time check for scoped_cond_guard() (to use it only with conditional locsk), and general improvements for the patch.
Big thanks to David Lechner for idea to cover also scoped_cond_guard().
Signed-off-by: Przemek Kitszel przemyslaw.kitszel@intel.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Dmitry Torokhov dmitry.torokhov@gmail.com Link: https://lkml.kernel.org/r/20241018113823.171256-1-przemyslaw.kitszel@intel.c... Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/cleanup.h | 48 ++++++++++++++++++++++++++++++++++------- 1 file changed, 40 insertions(+), 8 deletions(-)
diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h index d9e613803df15..ce7c9524c9f18 100644 --- a/include/linux/cleanup.h +++ b/include/linux/cleanup.h @@ -149,14 +149,20 @@ static inline class_##_name##_t class_##_name##ext##_constructor(_init_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(_name, _type, _lock, _unlock) \ + __DEFINE_CLASS_IS_CONDITIONAL(_name, false); \ DEFINE_CLASS(_name, _type, if (_T) { _unlock; }, ({ _lock; _T; }), _type _T); \ static inline void * class_##_name##_lock_ptr(class_##_name##_t *_T) \ { return *_T; }
#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) \ @@ -167,17 +173,40 @@ static inline class_##_name##_t class_##_name##ext##_constructor(_init_args) \ 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...) \ - for (CLASS(_name, scope)(args), \ - *done = NULL; __guard_ptr(_name)(&scope) && !done; done = (void *)1) +#define scoped_guard(_name, args...) \ + __scoped_guard(_name, __UNIQUE_ID(label), args)
-#define scoped_cond_guard(_name, _fail, args...) \ - for (CLASS(_name, scope)(args), \ - *done = NULL; !done; done = (void *)1) \ - if (!__guard_ptr(_name)(&scope)) _fail; \ - else +#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 @@ -233,14 +262,17 @@ static inline class_##_name##_t class_##_name##_constructor(void) \ }
#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; \