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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: Alexander Potapenko <glider@google.com>
Tested-by: Sodagudi Prasad <psodagud@codeaurora.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Alexander Potapenko 2017-07-19 20:27:30 +02:00 committed by Linus Torvalds
parent e06fdaf40a
commit beaec533fc
1 changed files with 19 additions and 2 deletions
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21
include/linux/llist.h
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@ -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)