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authorJens Axboe <axboe@kernel.dk>2023-09-28 07:47:07 -0600
committerJens Axboe <axboe@kernel.dk>2023-09-28 07:47:07 -0600
commit52e856c38761bae0cea09b25cfbb4d46cd930d45 (patch)
treee94c5b41e4ea4c8f95b993c6d875e2e7db78bbf8 /include/linux/cleanup.h
parent73c7e7a91f041f4c2e3c0db1e727163b331c60c9 (diff)
parentcfa92b6d52071aaa8f27d21affdcb14e7448fbc1 (diff)
Merge branch 'locking/core' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into io_uring-futex
Pull in locking/core from the tip tree, to get the futex2 dependencies from Peter Zijlstra. * 'locking/core' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (24 commits) locking/ww_mutex/test: Make sure we bail out instead of livelock locking/ww_mutex/test: Fix potential workqueue corruption locking/ww_mutex/test: Use prng instead of rng to avoid hangs at bootup futex: Add sys_futex_requeue() futex: Add flags2 argument to futex_requeue() futex: Propagate flags into get_futex_key() futex: Add sys_futex_wait() futex: FLAGS_STRICT futex: Add sys_futex_wake() futex: Validate futex value against futex size futex: Flag conversion futex: Extend the FUTEX2 flags futex: Clarify FUTEX2 flags asm-generic: ticket-lock: Optimize arch_spin_value_unlocked() futex/pi: Fix recursive rt_mutex waiter state locking/rtmutex: Add a lockdep assert to catch potential nested blocking locking/rtmutex: Use rt_mutex specific scheduler helpers sched: Provide rt_mutex specific scheduler helpers sched: Extract __schedule_loop() locking/rtmutex: Avoid unconditional slowpath for DEBUG_RT_MUTEXES ...
Diffstat (limited to 'include/linux/cleanup.h')
-rw-r--r--include/linux/cleanup.h39
1 files changed, 36 insertions, 3 deletions
diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h
index 53f1a7a932b0..9f1a9c455b68 100644
--- a/include/linux/cleanup.h
+++ b/include/linux/cleanup.h
@@ -7,8 +7,9 @@
/*
* 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.
+ * 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.
@@ -17,6 +18,9 @@
* 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().
*
@@ -24,6 +28,8 @@
*
* DEFINE_FREE(kfree, void *, if (_T) kfree(_T))
*
+ * void *alloc_obj(...)
+ * {
* struct obj *p __free(kfree) = kmalloc(...);
* if (!p)
* return NULL;
@@ -32,6 +38,24 @@
* 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) \
@@ -39,8 +63,17 @@
#define __free(_name) __cleanup(__free_##_name)
+#define __get_and_null_ptr(p) \
+ ({ __auto_type __ptr = &(p); \
+ __auto_type __val = *__ptr; \
+ *__ptr = NULL; __val; })
+
+static inline __must_check
+const volatile void * __must_check_fn(const volatile void *val)
+{ return val; }
+
#define no_free_ptr(p) \
- ({ __auto_type __ptr = (p); (p) = NULL; __ptr; })
+ ((typeof(p)) __must_check_fn(__get_and_null_ptr(p)))
#define return_ptr(p) return no_free_ptr(p)