staging: lustre: convert lov_pool to use rhashtable

The pools hashtable can be implemented using
the rhashtable implementation in lib.
This has the benefit that lookups are lock-free.

We need to use kfree_rcu() to free a pool so
that a lookup racing with a deletion will not access
freed memory.

rhashtable has no combined lookup-and-delete interface,
but as the lookup is lockless and the chains are short,
this brings little cost.  Even if a lookup finds a pool,
we must be prepared for the delete to fail to find it,
as we might race with another thread doing a delete.

We use atomic_inc_not_zero() after finding a pool in the
hash table and if that fails, we must have raced with a
deletion, so we treat the lookup as a failure.

Use hashlen_string() rather than a hand-crafted hash
function.
Note that the pool_name, and the search key, are
guaranteed to be nul terminated.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/staging/lustre/lustre/include/obd.h b/drivers/staging/lustre/lustre/include/obd.h
index 48cf7ab..7e1de03 100644
--- a/drivers/staging/lustre/lustre/include/obd.h
+++ b/drivers/staging/lustre/lustre/include/obd.h
@@ -46,6 +46,8 @@
 #include <lustre_intent.h>
 #include <cl_object.h>
 
+#include <linux/rhashtable.h>
+
 #define MAX_OBD_DEVICES 8192
 
 struct osc_async_rc {
@@ -383,7 +385,7 @@ struct lov_obd {
 	__u32		   lov_tgt_size;   /* size of tgts array */
 	int		     lov_connects;
 	int		     lov_pool_count;
-	struct cfs_hash	     *lov_pools_hash_body; /* used for key access */
+	struct rhashtable	lov_pools_hash_body; /* used for key access */
 	struct list_head	lov_pool_list; /* used for sequential access */
 	struct dentry		*lov_pool_debugfs_entry;
 	enum lustre_sec_part    lov_sp_me;