afs: Overhaul permit caching

Overhaul permit caching in AFS by making it per-vnode and sharing permit
lists where possible.

When most of the fileserver operations are called, they return a status
structure indicating the (revised) details of the vnode or vnodes involved
in the operation.  This includes the access mark derived from the ACL
(named CallerAccess in the protocol definition file).  This is cacheable
and if the ACL changes, the server will tell us that it is breaking the
callback promise, at which point we can discard the currently cached
permits.

With this patch, the afs_permits structure has, at the end, an array of
{ key, CallerAccess } elements, sorted by key pointer.  This is then cached
in a hash table so that it can be shared between vnodes with the same
access permits.

Permit lists can only be shared if they contain the exact same set of
key->CallerAccess mappings.

Note that that table is global rather than being per-net_ns.  If the keys
in a permit list cross net_ns boundaries, there is no problem sharing the
cached permits, since the permits are just integer masks.

Since permit lists pin keys, the permit cache also makes it easier for a
future patch to find all occurrences of a key and remove them by means of
setting the afs_permits::invalidated flag and then clearing the appropriate
key pointer.  In such an event, memory barriers will need adding.

Lastly, the permit caching is skipped if the server has sent either a
vnode-specific or an entire-server callback since the start of the
operation.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 15 insertions, 12 deletions

diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index e3c9943..7c31866 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -389,8 +389,7 @@ struct afs_vnode {
 #ifdef CONFIG_AFS_FSCACHE
 	struct fscache_cookie	*cache;		/* caching cookie */
 #endif
-	struct afs_permits	*permits;	/* cache of permits so far obtained */
-	struct mutex		permits_lock;	/* lock for altering permits list */
+	struct afs_permits	*permit_cache;	/* cache of permits so far obtained */
 	struct mutex		validate_lock;	/* lock for validating this vnode */
 	wait_queue_head_t	update_waitq;	/* status fetch waitqueue */
 	int			update_cnt;	/* number of outstanding ops that will update the
@@ -411,8 +410,6 @@ struct afs_vnode {
 #define AFS_VNODE_AUTOCELL	10		/* set if Vnode is an auto mount point */
 #define AFS_VNODE_PSEUDODIR	11		/* set if Vnode is a pseudo directory */
 
-	long			acl_order;	/* ACL check count (callback break count) */
-
 	struct list_head	writebacks;	/* alterations in pagecache that need writing */
 	struct list_head	pending_locks;	/* locks waiting to be granted */
 	struct list_head	granted_locks;	/* locks granted on this file */
@@ -435,16 +432,21 @@ struct afs_vnode {
  */
 struct afs_permit {
 	struct key		*key;		/* RxRPC ticket holding a security context */
-	afs_access_t		access_mask;	/* access mask for this key */
+	afs_access_t		access;		/* CallerAccess value for this key */
 };
 
 /*
- * cache of security records from attempts to access a vnode
+ * Immutable cache of CallerAccess records from attempts to access vnodes.
+ * These may be shared between multiple vnodes.
  */
 struct afs_permits {
-	struct rcu_head		rcu;		/* disposal procedure */
-	int			count;		/* number of records */
-	struct afs_permit	permits[0];	/* the permits so far examined */
+	struct rcu_head		rcu;
+	struct hlist_node	hash_node;	/* Link in hash */
+	unsigned long		h;		/* Hash value for this permit list */
+	refcount_t		usage;
+	unsigned short		nr_permits;	/* Number of records */
+	bool			invalidated;	/* Invalidated due to key change */
+	struct afs_permit	permits[];	/* List of permits sorted by key pointer */
 };
 
 /*
@@ -682,11 +684,13 @@ static inline int afs_transfer_reply(struct afs_call *call)
 /*
  * security.c
  */
+extern void afs_put_permits(struct afs_permits *);
 extern void afs_clear_permits(struct afs_vnode *);
-extern void afs_cache_permit(struct afs_vnode *, struct key *, long);
+extern void afs_cache_permit(struct afs_vnode *, struct key *, unsigned int);
 extern void afs_zap_permits(struct rcu_head *);
 extern struct key *afs_request_key(struct afs_cell *);
 extern int afs_permission(struct inode *, int);
+extern void __exit afs_clean_up_permit_cache(void);
 
 /*
  * server.c
@@ -757,8 +761,7 @@ static inline struct inode *AFS_VNODE_TO_I(struct afs_vnode *vnode)
 
 extern void afs_vnode_finalise_status_update(struct afs_vnode *,
 					     struct afs_server *);
-extern int afs_vnode_fetch_status(struct afs_vnode *, struct afs_vnode *,
-				  struct key *, bool);
+extern int afs_vnode_fetch_status(struct afs_vnode *, struct key *, bool);
 extern int afs_vnode_fetch_data(struct afs_vnode *, struct key *,
 				struct afs_read *);
 extern int afs_vnode_create(struct afs_vnode *, struct key *, const char *,