compiler-context-analysys: Add __cond_releases()

Useful for things like unlock fastpaths, which on success release the
lock.

Suggested-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Marco Elver <elver@google.com>
Link: https://patch.msgid.link/20260121111213.634625032@infradead.org

diff --git a/include/linux/compiler-context-analysis.h b/include/linux/compiler-context-analysis.h
index 00c074a2ccb0957696cbb71fe89d22ce7472dfb7..a9317571e6aff3a8d09adeaa9d74e0826d0ca074 100644 (file)
--- a/include/linux/compiler-context-analysis.h
+++ b/include/linux/compiler-context-analysis.h
@@ -320,6 +320,38 @@ static inline void _context_unsafe_alias(void **p) { }
  */
 #define __releases(...)                __releases_ctx_lock(__VA_ARGS__)
 
+/*
+ * Clang's analysis does not care precisely about the value, only that it is
+ * either zero or non-zero. So the __cond_acquires() interface might be
+ * misleading if we say that @ret is the value returned if acquired. Instead,
+ * provide symbolic variants which we translate.
+ */
+#define __cond_acquires_impl_not_true(x, ...)     __try_acquires##__VA_ARGS__##_ctx_lock(0, x)
+#define __cond_acquires_impl_not_false(x, ...)    __try_acquires##__VA_ARGS__##_ctx_lock(1, x)
+#define __cond_acquires_impl_not_nonzero(x, ...)  __try_acquires##__VA_ARGS__##_ctx_lock(0, x)
+#define __cond_acquires_impl_not_0(x, ...)        __try_acquires##__VA_ARGS__##_ctx_lock(1, x)
+#define __cond_acquires_impl_not_nonnull(x, ...)  __try_acquires##__VA_ARGS__##_ctx_lock(0, x)
+#define __cond_acquires_impl_not_NULL(x, ...)     __try_acquires##__VA_ARGS__##_ctx_lock(1, x)
+
+/**
+ * __cond_releases() - function attribute, function conditionally
+ *                     releases a context lock exclusively
+ * @ret: abstract value returned by function if context lock releases
+ * @x: context lock instance pointer
+ *
+ * Function attribute declaring that the function conditionally releases the
+ * given context lock instance @x exclusively. The associated context(s) must
+ * be active on entry. The function return value @ret denotes when the context
+ * lock is released.
+ *
+ * @ret may be one of: true, false, nonzero, 0, nonnull, NULL.
+ *
+ * NOTE: clang does not have a native attribute for this; instead implement
+ *       it as an unconditional release and a conditional acquire for the
+ *       inverted condition -- which is semantically equivalent.
+ */
+#define __cond_releases(ret, x) __releases(x) __cond_acquires_impl_not_##ret(x)
+
 /**
  * __acquire() - function to acquire context lock exclusively
  * @x: context lock instance pointer