nfsd41: sessionid hashing

Simple sessionid hashing using its monotonically increasing sequence number.

Locking considerations:
sessionid_hashtbl access is controlled by the sessionid_lock spin lock.
It must be taken for insert, delete, and lookup.
nfsd4_sequence looks up the session id and if the session is found,
it calls nfsd4_get_session (still under the sessionid_lock).
nfsd4_destroy_session calls nfsd4_put_session after unhashing
it, so when the session's kref reaches zero it's going to get freed.

Signed-off-by: Benny Halevy <bhalevy@panasas.com>
[we don't use a prime for sessionid hash table size]
[use sessionid_lock spin lock]
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

2 files changed, 61 insertions, 1 deletions

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index f23385b13065..fc20e1f38d75 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -382,11 +382,62 @@ static void release_openowner(struct nfs4_stateowner *sop)
         nfs4_put_stateowner(sop);
 }
 
+static DEFINE_SPINLOCK(sessionid_lock);
+#define SESSION_HASH_SIZE       512
+static struct list_head sessionid_hashtbl[SESSION_HASH_SIZE];
+
+static inline int
+hash_sessionid(struct nfs4_sessionid *sessionid)
+{
+        struct nfsd4_sessionid *sid = (struct nfsd4_sessionid *)sessionid;
+
+        return sid->sequence % SESSION_HASH_SIZE;
+}
+
+static inline void
+dump_sessionid(const char *fn, struct nfs4_sessionid *sessionid)
+{
+        u32 *ptr = (u32 *)(&sessionid->data[0]);
+        dprintk("%s: %u:%u:%u:%u\n", fn, ptr[0], ptr[1], ptr[2], ptr[3]);
+}
+
+/* caller must hold sessionid_lock */
+static struct nfsd4_session *
+find_in_sessionid_hashtbl(struct nfs4_sessionid *sessionid)
+{
+        struct nfsd4_session *elem;
+        int idx;
+
+        dump_sessionid(__func__, sessionid);
+        idx = hash_sessionid(sessionid);
+        dprintk("%s: idx is %d\n", __func__, idx);
+        /* Search in the appropriate list */
+        list_for_each_entry(elem, &sessionid_hashtbl[idx], se_hash) {
+                dump_sessionid("list traversal", &elem->se_sessionid);
+                if (!memcmp(elem->se_sessionid.data, sessionid->data,
+                            NFS4_MAX_SESSIONID_LEN)) {
+                        return elem;
+                }
+        }
+
+        dprintk("%s: session not found\n", __func__);
+        return NULL;
+}
+
+/* caller must hold sessionid_lock */
 static void
-release_session(struct nfsd4_session *ses)
+unhash_session(struct nfsd4_session *ses)
 {
         list_del(&ses->se_hash);
         list_del(&ses->se_perclnt);
+}
+
+static void
+release_session(struct nfsd4_session *ses)
+{
+        spin_lock(&sessionid_lock);
+        unhash_session(ses);
+        spin_unlock(&sessionid_lock);
         nfsd4_put_session(ses);
 }
 
@@ -3205,6 +3256,8 @@ nfs4_state_init(void)
                 INIT_LIST_HEAD(&unconf_str_hashtbl[i]);
                 INIT_LIST_HEAD(&unconf_id_hashtbl[i]);
         }
+        for (i = 0; i < SESSION_HASH_SIZE; i++)
+                INIT_LIST_HEAD(&sessionid_hashtbl[i]);
         for (i = 0; i < FILE_HASH_SIZE; i++) {
                 INIT_LIST_HEAD(&file_hashtbl[i]);
         }
diff --git a/include/linux/nfsd/state.h b/include/linux/nfsd/state.h
index 7faefc7c9d9a..5b3a6660f3af 100644
--- a/include/linux/nfsd/state.h
+++ b/include/linux/nfsd/state.h
@@ -132,6 +132,13 @@ nfsd4_get_session(struct nfsd4_session *ses)
         kref_get(&ses->se_ref);
 }
 
+/* formatted contents of nfs4_sessionid */
+struct nfsd4_sessionid {
+        clientid_t      clientid;
+        u32             sequence;
+        u32             reserved;
+};
+
 #define HEXDIR_LEN     33 /* hex version of 16 byte md5 of cl_name plus '\0' */
 
 /*