lib min_heap: improve type safety in min_heap macros by using container_of

Patch series "lib min_heap: Improve min_heap safety, testing, and
documentation".

Improve the min heap implementation by enhancing type safety with
container_of, reducing the attack vector by replacing test function calls
with inline variants, and adding a brief API introduction in min_heap.h.
It also includes author information in
Documentation/core-api/min_heap.rst.


This patch (of 4):

The current implementation of min_heap macros uses explicit casting to
min_heap_char *, which prevents the compiler from detecting incorrect
pointer types. This can lead to errors if non-min_heap pointers are
passed inadvertently.

To enhance safety, replace all explicit casts to min_heap_char * with the
use of container_of(&(_heap)->nr, min_heap_char, nr). This approach
ensures that the _heap parameter is indeed a min_heap_char-compatible
structure, allowing the compiler to catch improper usages.

Link: https://lkml.kernel.org/r/[e-mail]
Link: https://lore.kernel.org/lkml/CAMuHMdVO5DPuD9HYWBFqKDHphx7+0BEhreUxtVC40A=[e-mail]
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Kuan-Wei Chiu <[e-mail]>
Suggested-by: Geert Uytterhoeven <[e-mail]>
Cc: Ching-Chun (Jim) Huang <[e-mail]>
Cc: Jonathan Corbet <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/linux/min_heap.h

···
 }
 
 #define min_heap_init_inline(_heap, _data, _size)	\
-	__min_heap_init_inline((min_heap_char *)_heap, _data, _size)
+	__min_heap_init_inline(container_of(&(_heap)->nr, min_heap_char, nr), _data, _size)
 
 /* Get the minimum element from the heap. */
 static __always_inline
···
 }
 
 #define min_heap_peek_inline(_heap)	\
-	(__minheap_cast(_heap) __min_heap_peek_inline((min_heap_char *)_heap))
+	(__minheap_cast(_heap)	\
+	 __min_heap_peek_inline(container_of(&(_heap)->nr, min_heap_char, nr)))
 
 /* Check if the heap is full. */
 static __always_inline
···
 }
 
 #define min_heap_full_inline(_heap)	\
-	__min_heap_full_inline((min_heap_char *)_heap)
+	__min_heap_full_inline(container_of(&(_heap)->nr, min_heap_char, nr))
 
 /* Sift the element at pos down the heap. */
 static __always_inline
···
 }
 
 #define min_heap_sift_down_inline(_heap, _pos, _func, _args)	\
-	__min_heap_sift_down_inline((min_heap_char *)_heap, _pos, __minheap_obj_size(_heap),	\
-				    _func, _args)
+	__min_heap_sift_down_inline(container_of(&(_heap)->nr, min_heap_char, nr), _pos,	\
+				    __minheap_obj_size(_heap), _func, _args)
 
 /* Sift up ith element from the heap, O(log2(nr)). */
 static __always_inline
···
 }
 
 #define min_heap_sift_up_inline(_heap, _idx, _func, _args)	\
-	__min_heap_sift_up_inline((min_heap_char *)_heap, __minheap_obj_size(_heap), _idx,	\
-				  _func, _args)
+	__min_heap_sift_up_inline(container_of(&(_heap)->nr, min_heap_char, nr),	\
+				  __minheap_obj_size(_heap), _idx, _func, _args)
 
 /* Floyd's approach to heapification that is O(nr). */
 static __always_inline
···
 }
 
 #define min_heapify_all_inline(_heap, _func, _args)	\
-	__min_heapify_all_inline((min_heap_char *)_heap, __minheap_obj_size(_heap), _func, _args)
+	__min_heapify_all_inline(container_of(&(_heap)->nr, min_heap_char, nr),	\
+				 __minheap_obj_size(_heap), _func, _args)
 
 /* Remove minimum element from the heap, O(log2(nr)). */
 static __always_inline
···
 }
 
 #define min_heap_pop_inline(_heap, _func, _args)	\
-	__min_heap_pop_inline((min_heap_char *)_heap, __minheap_obj_size(_heap), _func, _args)
+	__min_heap_pop_inline(container_of(&(_heap)->nr, min_heap_char, nr),	\
+			      __minheap_obj_size(_heap), _func, _args)
 
 /*
  * Remove the minimum element and then push the given element. The
···
 }
 
 #define min_heap_pop_push_inline(_heap, _element, _func, _args)	\
-	__min_heap_pop_push_inline((min_heap_char *)_heap, _element, __minheap_obj_size(_heap),	\
-				   _func, _args)
+	__min_heap_pop_push_inline(container_of(&(_heap)->nr, min_heap_char, nr), _element,	\
+				   __minheap_obj_size(_heap), _func, _args)
 
 /* Push an element on to the heap, O(log2(nr)). */
 static __always_inline
···
 }
 
 #define min_heap_push_inline(_heap, _element, _func, _args)	\
-	__min_heap_push_inline((min_heap_char *)_heap, _element, __minheap_obj_size(_heap),	\
-			       _func, _args)
+	__min_heap_push_inline(container_of(&(_heap)->nr, min_heap_char, nr), _element,	\
+					    __minheap_obj_size(_heap), _func, _args)
 
 /* Remove ith element from the heap, O(log2(nr)). */
 static __always_inline
···
 }
 
 #define min_heap_del_inline(_heap, _idx, _func, _args)	\
-	__min_heap_del_inline((min_heap_char *)_heap, __minheap_obj_size(_heap), _idx,	\
-			      _func, _args)
+	__min_heap_del_inline(container_of(&(_heap)->nr, min_heap_char, nr),	\
+			      __minheap_obj_size(_heap), _idx, _func, _args)
 
 void __min_heap_init(min_heap_char *heap, void *data, int size);
 void *__min_heap_peek(struct min_heap_char *heap);
···
 		    const struct min_heap_callbacks *func, void *args);
 
 #define min_heap_init(_heap, _data, _size)	\
-	__min_heap_init((min_heap_char *)_heap, _data, _size)
+	__min_heap_init(container_of(&(_heap)->nr, min_heap_char, nr), _data, _size)
 #define min_heap_peek(_heap)	\
-	(__minheap_cast(_heap) __min_heap_peek((min_heap_char *)_heap))
+	(__minheap_cast(_heap) __min_heap_peek(container_of(&(_heap)->nr, min_heap_char, nr)))
 #define min_heap_full(_heap)	\
-	__min_heap_full((min_heap_char *)_heap)
+	__min_heap_full(container_of(&(_heap)->nr, min_heap_char, nr))
 #define min_heap_sift_down(_heap, _pos, _func, _args)	\
-	__min_heap_sift_down((min_heap_char *)_heap, _pos, __minheap_obj_size(_heap), _func, _args)
+	__min_heap_sift_down(container_of(&(_heap)->nr, min_heap_char, nr), _pos,	\
+			     __minheap_obj_size(_heap), _func, _args)
 #define min_heap_sift_up(_heap, _idx, _func, _args)	\
-	__min_heap_sift_up((min_heap_char *)_heap, __minheap_obj_size(_heap), _idx, _func, _args)
+	__min_heap_sift_up(container_of(&(_heap)->nr, min_heap_char, nr),	\
+			   __minheap_obj_size(_heap), _idx, _func, _args)
 #define min_heapify_all(_heap, _func, _args)	\
-	__min_heapify_all((min_heap_char *)_heap, __minheap_obj_size(_heap), _func, _args)
+	__min_heapify_all(container_of(&(_heap)->nr, min_heap_char, nr),	\
+			  __minheap_obj_size(_heap), _func, _args)
 #define min_heap_pop(_heap, _func, _args)	\
-	__min_heap_pop((min_heap_char *)_heap, __minheap_obj_size(_heap), _func, _args)
+	__min_heap_pop(container_of(&(_heap)->nr, min_heap_char, nr),	\
+		       __minheap_obj_size(_heap), _func, _args)
 #define min_heap_pop_push(_heap, _element, _func, _args)	\
-	__min_heap_pop_push((min_heap_char *)_heap, _element, __minheap_obj_size(_heap),	\
-			    _func, _args)
+	__min_heap_pop_push(container_of(&(_heap)->nr, min_heap_char, nr), _element,	\
+			    __minheap_obj_size(_heap), _func, _args)
 #define min_heap_push(_heap, _element, _func, _args)	\
-	__min_heap_push((min_heap_char *)_heap, _element, __minheap_obj_size(_heap), _func, _args)
+	__min_heap_push(container_of(&(_heap)->nr, min_heap_char, nr), _element,	\
+			__minheap_obj_size(_heap), _func, _args)
 #define min_heap_del(_heap, _idx, _func, _args)	\
-	__min_heap_del((min_heap_char *)_heap, __minheap_obj_size(_heap), _idx, _func, _args)
+	__min_heap_del(container_of(&(_heap)->nr, min_heap_char, nr),	\
+		       __minheap_obj_size(_heap), _idx, _func, _args)
 
 #endif /* _LINUX_MIN_HEAP_H */