From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f199.google.com (mail-wr0-f199.google.com [209.85.128.199]) by kanga.kvack.org (Postfix) with ESMTP id 5171F6B025F for ; Wed, 19 Jul 2017 14:28:34 -0400 (EDT) Received: by mail-wr0-f199.google.com with SMTP id z53so8863995wrz.10 for ; Wed, 19 Jul 2017 11:28:34 -0700 (PDT) Received: from mail-wm0-x230.google.com (mail-wm0-x230.google.com. [2a00:1450:400c:c09::230]) by mx.google.com with ESMTPS id z37si5023149wrb.382.2017.07.19.11.28.32 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 19 Jul 2017 11:28:32 -0700 (PDT) Received: by mail-wm0-x230.google.com with SMTP id k69so6157611wmc.1 for ; Wed, 19 Jul 2017 11:28:32 -0700 (PDT) From: Alexander Potapenko Subject: [PATCH] llist: clang: introduce member_address_is_nonnull() Date: Wed, 19 Jul 2017 20:27:30 +0200 Message-Id: <20170719182730.65794-1-glider@google.com> Sender: owner-linux-mm@kvack.org List-ID: To: dvyukov@google.com, kcc@google.com, akpm@linux-foundation.org, torvalds@linux-foundation.org, mingo@elte.hu Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, md@google.com, ndesaulniers@google.com, ghackmann@google.com, mka@google.com 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: Alexander Potapenko --- include/linux/llist.h | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-) diff --git a/include/linux/llist.h b/include/linux/llist.h index d11738110a7a..a7cdaeddad35 100644 --- a/include/linux/llist.h +++ b/include/linux/llist.h @@ -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) -- 2.14.0.rc0.284.gd933b75aa4-goog -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org