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Commit beaec533 authored by Alexander Potapenko's avatar Alexander Potapenko Committed by Linus Torvalds
Browse files

llist: clang: introduce member_address_is_nonnull() 



Currently llist_for_each_entry() and llist_for_each_entry_safe() iterate
until &pos->member != NULL.  But when building the kernel with Clang,
the compiler assumes &pos->member cannot be NULL if the member's offset
is greater than 0 (which would be equivalent to the object being
non-contiguous in memory).  Therefore the loop condition is always true,
and the loops become infinite.

To work around this, introduce the member_address_is_nonnull() macro,
which casts object pointer to uintptr_t, thus letting the member pointer
to be NULL.

Signed-off-by: default avatarAlexander Potapenko <glider@google.com>
Tested-by: default avatarSodagudi Prasad <psodagud@codeaurora.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e06fdaf4

include/linux/llist.h

+19 −2
Original line number Diff line number Diff line
@@ -92,6 +92,23 @@ static inline void init_llist_head(struct llist_head *list) 
#define llist_entry(ptr, type, member)		\

	container_of(ptr, type, member)



/**

 * member_address_is_nonnull - check whether the member address is not NULL

 * @ptr:	the object pointer (struct type * that contains the llist_node)

 * @member:	the name of the llist_node within the struct.

 *

 * This macro is conceptually the same as

 *	&ptr->member != NULL

 * but it works around the fact that compilers can decide that taking a member

 * address is never a NULL pointer.

 *

 * Real objects that start at a high address and have a member at NULL are

 * unlikely to exist, but such pointers may be returned e.g. by the

 * container_of() macro.

 */

#define member_address_is_nonnull(ptr, member)	\

	((uintptr_t)(ptr) + offsetof(typeof(*(ptr)), member) != 0)



/**

 * llist_for_each - iterate over some deleted entries of a lock-less list

 * @pos:	the &struct llist_node to use as a loop cursor
@@ -145,7 +162,7 @@ static inline void init_llist_head(struct llist_head *list) 
 */

#define llist_for_each_entry(pos, node, member)				\

	for ((pos) = llist_entry((node), typeof(*(pos)), member);	\

	     &(pos)->member != NULL;					\

	     member_address_is_nonnull(pos, member);			\

	     (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))



/**
@@ -167,7 +184,7 @@ static inline void init_llist_head(struct llist_head *list) 
 */

#define llist_for_each_entry_safe(pos, n, node, member)			       \

	for (pos = llist_entry((node), typeof(*pos), member);		       \

	     &pos->member != NULL &&					       \

	     member_address_is_nonnull(pos, member) &&			       \

	        (n = llist_entry(pos->member.next, typeof(*n), member), true); \

	     pos = n)