[PATCH 2/4] rhashtable: allow rht_bucket_var to return NULL.

NeilBrown
2019-04-01T23:08:31Z

Rather than returning a pointer to a static nulls, rht_bucket_var()
now returns NULL if the bucket doesn't exist.
This will make the next patch, which stores a bitlock in the
bucket pointer, somewhat cleaner.

This change involves introducing __rht_bucket_nested() which is
like rht_bucket_nested(), but doesn't provide the static nulls,
and changing rht_bucket_nested() to call this and possible
provide a static nulls - as is still needed for the non-var case.

Signed-off-by: NeilBrown <neilb@suse.com>
---
include/linux/rhashtable.h | 11 +++++++++--
lib/rhashtable.c | 29 ++++++++++++++++++++---------
2 files changed, 29 insertions(+), 11 deletions(-)

diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 86dfa417848d..0c9175aeab8a 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -265,6 +265,8 @@ void rhashtable_destroy(struct rhashtable *ht);

struct rhash_head __rcu **rht_bucket_nested(const struct bucket_table *tbl,
unsigned int hash);
+struct rhash_head __rcu **__rht_bucket_nested(const struct bucket_table *tbl,
+ unsigned int hash);
struct rhash_head __rcu **rht_bucket_nested_insert(struct rhashtable *ht,
struct bucket_table *tbl,
unsigned int hash);
@@ -294,7 +296,7 @@ static inline struct rhash_head __rcu *const *rht_bucket(
static inline struct rhash_head __rcu **rht_bucket_var(
struct bucket_table *tbl, unsigned int hash)
{
- return unlikely(tbl->nest) ? rht_bucket_nested(tbl, hash) :
+ return unlikely(tbl->nest) ? __rht_bucket_nested(tbl, hash) :
&tbl->buckets[hash];
}

@@ -890,6 +892,8 @@ static inline int __rhashtable_remove_fast_one(
spin_lock_bh(lock);

pprev = rht_bucket_var(tbl, hash);
+ if (!pprev)
+ goto out;
rht_for_each_from(he, *pprev, tbl, hash) {
struct rhlist_head *list;

@@ -934,6 +938,7 @@ static inline int __rhashtable_remove_fast_one(
break;
}

+out:
spin_unlock_bh(lock);

if (err > 0) {
@@ -1042,6 +1047,8 @@ static inline int __rhashtable_replace_fast(
spin_lock_bh(lock);

pprev = rht_bucket_var(tbl, hash);
+ if (!pprev)
+ goto out;
rht_for_each_from(he, *pprev, tbl, hash) {
if (he != obj_old) {
pprev = &he->next;
@@ -1053,7 +1060,7 @@ static inline int __rhashtable_replace_fast(
err = 0;
break;
}
-
+out:
spin_unlock_bh(lock);

return err;
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 6c4f5c8e9baa..b28fdd560ea9 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -237,8 +237,10 @@ static int rhashtable_rehash_one(struct rhashtable *ht, unsigned int old_hash)
goto out;

err = -ENOENT;
+ if (!pprev)
+ goto out;

- rht_for_each(entry, old_tbl, old_hash) {
+ rht_for_each_from(entry, *pprev, old_tbl, old_hash) {
err = 0;
next = rht_dereference_bucket(entry->next, old_tbl, old_hash);

@@ -496,6 +498,8 @@ static void *rhashtable_lookup_one(struct rhashtable *ht,

elasticity = RHT_ELASTICITY;
pprev = rht_bucket_var(tbl, hash);
+ if (!pprev)
+ return ERR_PTR(-ENOENT);
rht_for_each_from(head, *pprev, tbl, hash) {
struct rhlist_head *list;
struct rhlist_head *plist;
@@ -1161,11 +1165,10 @@ void rhashtable_destroy(struct rhashtable *ht)
}
EXPORT_SYMBOL_GPL(rhashtable_destroy);

-struct rhash_head __rcu **rht_bucket_nested(const struct bucket_table *tbl,
- unsigned int hash)
+struct rhash_head __rcu **__rht_bucket_nested(const struct bucket_table *tbl,
+ unsigned int hash)
{
const unsigned int shift = PAGE_SHIFT - ilog2(sizeof(void *));
- static struct rhash_head __rcu *rhnull;
unsigned int index = hash & ((1 << tbl->nest) - 1);
unsigned int size = tbl->size >> tbl->nest;
unsigned int subhash = hash;
@@ -1183,15 +1186,23 @@ struct rhash_head __rcu **rht_bucket_nested(const struct bucket_table *tbl,
subhash >>= shift;
}

- if (!ntbl) {
- if (!rhnull)
- INIT_RHT_NULLS_HEAD(rhnull);
- return &rhnull;
- }
+ if (!ntbl)
+ return NULL;

return &ntbl[subhash].bucket;

}
+EXPORT_SYMBOL_GPL(__rht_bucket_nested);
+
+struct rhash_head __rcu **rht_bucket_nested(const struct bucket_table *tbl,
+ unsigned int hash)
+{
+ static struct rhash_head __rcu *rhnull;
+
+ if (!rhnull)
+ INIT_RHT_NULLS_HEAD(rhnull);
+ return __rht_bucket_nested(tbl, hash) ?: &rhnull;
+}
EXPORT_SYMBOL_GPL(rht_bucket_nested);

struct rhash_head __rcu **rht_bucket_nested_insert(struct rhashtable *ht,