From: Madhuparna Bhowmik <madhuparnabhowmik04@xxxxxxxxx> There are instances in the linux kernel where the prev pointer of a list is accessed. Unlike list_next_rcu, a similar macro for accessing the prev pointer was not present. Therefore, directly accessing the prev pointer was causing sparse errors. One such example is the sparse error in fs/nfs/dir.c error: fs/nfs/dir.c:2353:14: error: incompatible types in comparison expression (different address spaces): fs/nfs/dir.c:2353:14: struct list_head [noderef] <asn:4> * fs/nfs/dir.c:2353:14: struct list_head * The error is caused due to the following line: lh = rcu_dereference(nfsi->access_cache_entry_lru.prev); After adding the macro, this error can be fixed as follows: lh = rcu_dereference(list_prev_rcu(&nfsi->access_cache_entry_lru)); Therefore, we think there is a need to add this macro to rculist.h. Suggested-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik04@xxxxxxxxx> --- include/linux/rculist.h | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/include/linux/rculist.h b/include/linux/rculist.h index 4b7ae1bf50b3..49eef8437753 100644 --- a/include/linux/rculist.h +++ b/include/linux/rculist.h @@ -40,6 +40,12 @@ static inline void INIT_LIST_HEAD_RCU(struct list_head *list) */ #define list_next_rcu(list) (*((struct list_head __rcu **)(&(list)->next))) +/* + * return the prev pointer of a list_head in an rcu safe + * way, we must not access it directly + */ +#define list_prev_rcu(list) (*((struct list_head __rcu **)(&(list)->prev))) + /* * Check during list traversal that we are within an RCU reader */ -- 2.17.1
