This is a note to let you know that I've just added the patch titled

llist: clang: introduce member_address_is_nonnull()

to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: llist-clang-introduce-member_address_is_nonnull.patch and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From beaec533fc2701a28a4d667f67c9f59c6e4e0d13 Mon Sep 17 00:00:00 2001

From: Alexander Potapenko glider@google.com Date: Wed, 19 Jul 2017 20:27:30 +0200 Subject: llist: clang: introduce member_address_is_nonnull()

From: Alexander Potapenko glider@google.com

commit beaec533fc2701a28a4d667f67c9f59c6e4e0d13 upstream.

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 glider@google.com Tested-by: Sodagudi Prasad psodagud@codeaurora.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- include/linux/llist.h | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-)

--- a/include/linux/llist.h +++ b/include/linux/llist.h @@ -88,6 +88,23 @@ static inline void init_llist_head(struc 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 * @node: the first entry of deleted list entries @@ -121,7 +138,7 @@ static inline void init_llist_head(struc */ #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))

/** @@ -143,7 +160,7 @@ static inline void init_llist_head(struc */ #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)

Patches currently in stable-queue which might be from glider@google.com are

queue-4.4/llist-clang-introduce-member_address_is_nonnull.patch