[PATCH 16/17] rhashtable: Convert to split_lock

[Matthew Wilcox (Oracle)]

NeilBrown noticed the same problem with bit spinlocks that I did,
but chose to solve it locally in the rhashtable implementation rather
than lift it all the way to the bit spin lock implementation.  Convert
rhashtables to use split_locks.

Signed-off-by: Matthew Wilcox (Oracle) <wi...@infradead.org>
Cc: NeilBrown <ne...@suse.de>
---
 include/linux/rhashtable.h | 20 +++++++-------------
 lib/rhashtable.c           |  5 +----
 2 files changed, 8 insertions(+), 17 deletions(-)

diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 68dab3e08aad..4df164fe6222 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -65,12 +65,11 @@ struct rhash_lock_head {};
  * struct bucket_table - Table of hash buckets
  * @size: Number of hash buckets
  * @nest: Number of bits of first-level nested table.
- * @rehash: Current bucket being rehashed
  * @hash_rnd: Random seed to fold into hash
  * @walkers: List of active walkers
  * @rcu: RCU structure for freeing the table
  * @future_tbl: Table under construction during rehashing
- * @ntbl: Nested table used when out of memory.
+ * @sl: Conceptual spinlock representing every per-bucket lock.
  * @buckets: size * hash buckets
  */
 struct bucket_table {
@@ -82,7 +81,7 @@ struct bucket_table {
 
        struct bucket_table __rcu *future_tbl;
 
-       struct lockdep_map      dep_map;
+       struct split_lock       sl;
 
        struct rhash_lock_head __rcu *buckets[] ____cacheline_aligned_in_smp;
 };
@@ -327,8 +326,7 @@ static inline void rht_lock(struct bucket_table *tbl,
                            struct rhash_lock_head __rcu **bkt)
 {
        local_bh_disable();
-       bit_spin_lock(0, (unsigned long *)bkt);
-       lock_map_acquire(&tbl->dep_map);
+       bit_spin_lock(0, (unsigned long *)bkt, &tbl->sl);
 }
 
 static inline void rht_lock_nested(struct bucket_table *tbl,
@@ -336,15 +334,13 @@ static inline void rht_lock_nested(struct bucket_table 
*tbl,
                                   unsigned int subclass)
 {
        local_bh_disable();
-       bit_spin_lock(0, (unsigned long *)bucket);
-       lock_acquire_exclusive(&tbl->dep_map, subclass, 0, NULL, _THIS_IP_);
+       bit_spin_lock_nested(0, (unsigned long *)bucket, &tbl->sl, subclass);
 }
 
 static inline void rht_unlock(struct bucket_table *tbl,
                              struct rhash_lock_head __rcu **bkt)
 {
-       lock_map_release(&tbl->dep_map);
-       bit_spin_unlock(0, (unsigned long *)bkt);
+       bit_spin_unlock(0, (unsigned long *)bkt, &tbl->sl);
        local_bh_enable();
 }
 
@@ -397,10 +393,8 @@ static inline void rht_assign_unlock(struct bucket_table 
*tbl,
 {
        if (rht_is_a_nulls(obj))
                obj = NULL;
-       lock_map_release(&tbl->dep_map);
-       rcu_assign_pointer(*bkt, (void *)obj);
-       preempt_enable();
-       __release(bitlock);
+       bit_spin_unlock_assign((unsigned long *)bkt, (unsigned long)obj,
+                               &tbl->sl);
        local_bh_enable();
 }
 
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index c949c1e3b87c..bfdb0bf87f99 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -179,7 +179,6 @@ static struct bucket_table *bucket_table_alloc(struct 
rhashtable *ht,
        struct bucket_table *tbl = NULL;
        size_t size;
        int i;
-       static struct lock_class_key __key;
 
        tbl = kvzalloc(struct_size(tbl, buckets, nbuckets), gfp);
 
@@ -193,10 +192,8 @@ static struct bucket_table *bucket_table_alloc(struct 
rhashtable *ht,
        if (tbl == NULL)
                return NULL;
 
-       lockdep_init_map(&tbl->dep_map, "rhashtable_bucket", &__key, 0);
-
+       split_lock_init(&tbl->sl);
        tbl->size = size;
-
        rcu_head_init(&tbl->rcu);
        INIT_LIST_HEAD(&tbl->walkers);
 
-- 
2.30.2