nfsd: allow for up to 32 callback session slots

nfsd currently only uses a single slot in the callback channel, which is
proving to be a bottleneck in some cases. Widen the callback channel to
a max of 32 slots (subject to the client's target_maxreqs value).

Change the cb_holds_slot boolean to an integer that tracks the current
slot number (with -1 meaning "unassigned").  Move the callback slot
tracking info into the session. Add a new u32 that acts as a bitmap to
track which slots are in use, and a u32 to track the latest callback
target_slotid that the client reports. To protect the new fields, add
a new per-session spinlock (the se_lock). Fix nfsd41_cb_get_slot to always
search for the lowest slotid (using ffs()).

Finally, convert the session->se_cb_seq_nr field into an array of
ints and add the necessary handling to ensure that the seqids get
reset when the slot table grows after shrinking.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

1 files changed, 9 insertions, 6 deletions

diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index 8092894e8f3c..e16bb3717fb9 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -71,8 +71,8 @@ struct nfsd4_callback {
 	struct work_struct cb_work;
 	int cb_seq_status;
 	int cb_status;
+	int cb_held_slot;
 	bool cb_need_restart;
-	bool cb_holds_slot;
 };
 
 struct nfsd4_callback_ops {
@@ -304,6 +304,9 @@ struct nfsd4_conn {
 	unsigned char cn_flags;
 };
 
+/* Maximum number of slots that nfsd will use in the backchannel */
+#define NFSD_BC_SLOT_TABLE_SIZE		(sizeof(u32) * 8)
+
 /*
  * Representation of a v4.1+ session. These are refcounted in a similar fashion
  * to the nfs4_client. References are only taken when the server is actively
@@ -311,6 +314,10 @@ struct nfsd4_conn {
  */
 struct nfsd4_session {
 	atomic_t		se_ref;
+	spinlock_t		se_lock;
+	u32			se_cb_slot_avail; /* bitmap of available slots */
+	u32			se_cb_highest_slot;	/* highest slot client wants */
+	u32			se_cb_prog;
 	bool			se_dead;
 	struct list_head	se_hash;	/* hash by sessionid */
 	struct list_head	se_perclnt;
@@ -319,8 +326,7 @@ struct nfsd4_session {
 	struct nfsd4_channel_attrs se_fchannel;
 	struct nfsd4_cb_sec	se_cb_sec;
 	struct list_head	se_conns;
-	u32			se_cb_prog;
-	u32			se_cb_seq_nr;
+	u32			se_cb_seq_nr[NFSD_BC_SLOT_TABLE_SIZE];
 	struct nfsd4_slot	*se_slots[];	/* forward channel slots */
 };
 
@@ -454,9 +460,6 @@ struct nfs4_client {
 	 */
 	struct dentry		*cl_nfsd_info_dentry;
 
-	/* for nfs41 callbacks */
-	/* We currently support a single back channel with a single slot */
-	unsigned long		cl_cb_slot_busy;
 	struct rpc_wait_queue	cl_cb_waitq;	/* backchannel callers may */
 						/* wait here for slots */
 	struct net		*net;