[pnfs] [PATCH 1/1] nfs41: Use bottom half spinlock in callback list processing

[Ricardo Labiaga]

From: Ricardo Labiaga <Ricardo.Labiaga at netapp.com>

Switch from reader/writers lock to spinlock for manipulation of the
backchannel preallocated lists.  Only the exclusive access writers lock
was being used so there's no need for readers/writers functionality.

Use bottom half spinlocks as well. Other spinlocks in xprt.c and xprtsock.c
during transport I/O are already bottom half.

Signed-off-by: Ricardo Labiaga <Ricardo.Labiaga at netapp.com>
---
 include/linux/sunrpc/xprt.h   |    2 +-
 net/sunrpc/backchannel_rqst.c |   16 ++++++++--------
 net/sunrpc/xprt.c             |    2 +-
 3 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h
index 763daf6..55b617d 100644
--- a/include/linux/sunrpc/xprt.h
+++ b/include/linux/sunrpc/xprt.h
@@ -180,7 +180,7 @@ struct rpc_xprt {
 	struct svc_serv		*serv;		/* The RPC service which will */
 						/* process the callback */
 	unsigned int		bc_alloc_count;	/* Total number of preallocs */
-	rwlock_t		bc_pa_lock;	/* Protects the preallocated */
+	spinlock_t		bc_pa_lock;	/* Protects the preallocated */
 						/* items */
 	struct list_head	bc_pa_list;	/* List of preallocated */
 						/* backchannel rpc_rqst's */
diff --git a/net/sunrpc/backchannel_rqst.c b/net/sunrpc/backchannel_rqst.c
index 09f90f9..660a666 100644
--- a/net/sunrpc/backchannel_rqst.c
+++ b/net/sunrpc/backchannel_rqst.c
@@ -146,10 +146,10 @@ int xprt_setup_backchannel(struct rpc_xprt *xprt, unsigned int min_reqs)
 	/*
 	 * Add the temporary list to the backchannel preallocation list
 	 */
-	write_lock(&xprt->bc_pa_lock);
+	spin_lock_bh(&xprt->bc_pa_lock);
 	list_splice(&tmp_list, &xprt->bc_pa_list);
 	xprt_inc_alloc_count(xprt, min_reqs);
-	write_unlock(&xprt->bc_pa_lock);
+	spin_unlock_bh(&xprt->bc_pa_lock);
 
 	dprintk("RPC:       setup backchannel transport done\n");
 	return 0;
@@ -182,7 +182,7 @@ void xprt_destroy_backchannel(struct rpc_xprt *xprt, unsigned int max_reqs)
 	dprintk("RPC:        destroy backchannel transport\n");
 
 	BUG_ON(max_reqs == 0);
-	write_lock(&xprt->bc_pa_lock);
+	spin_lock_bh(&xprt->bc_pa_lock);
 	xprt_dec_alloc_count(xprt, max_reqs);
 	list_for_each_entry_safe(req, tmp, &xprt->bc_pa_list,
 					  rq_bc_pa_list) {
@@ -191,7 +191,7 @@ void xprt_destroy_backchannel(struct rpc_xprt *xprt, unsigned int max_reqs)
 		if (--max_reqs == 0)
 			break;
 	}
-	write_unlock(&xprt->bc_pa_lock);
+	spin_unlock_bh(&xprt->bc_pa_lock);
 
 	dprintk("RPC:        backchannel list empty= %s\n",
 		list_empty(&xprt->bc_pa_list) ? "true" : "false");
@@ -211,7 +211,7 @@ struct rpc_rqst *xprt_alloc_bc_request(struct rpc_xprt *xprt)
 	struct rpc_rqst *req;
 
 	dprintk("RPC:       allocate a backchannel request\n");
-	write_lock(&xprt->bc_pa_lock);
+	spin_lock_bh(&xprt->bc_pa_lock);
 	if (!list_empty(&xprt->bc_pa_list)) {
 		req = list_first_entry(&xprt->bc_pa_list, struct rpc_rqst,
 				rq_bc_pa_list);
@@ -219,7 +219,7 @@ struct rpc_rqst *xprt_alloc_bc_request(struct rpc_xprt *xprt)
 	} else {
 		req = NULL;
 	}
-	write_unlock(&xprt->bc_pa_lock);
+	spin_unlock_bh(&xprt->bc_pa_lock);
 
 	if (req != NULL) {
 		set_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state);
@@ -261,9 +261,9 @@ void xprt_free_bc_request(struct rpc_rqst *req)
 	 * Return it to the list of preallocations so that it
 	 * may be reused by a new callback request.
 	 */
-	write_lock(&xprt->bc_pa_lock);
+	spin_lock_bh(&xprt->bc_pa_lock);
 	list_add(&req->rq_bc_pa_list, &xprt->bc_pa_list);
-	write_unlock(&xprt->bc_pa_lock);
+	spin_unlock_bh(&xprt->bc_pa_lock);
 }
 EXPORT_SYMBOL(xprt_free_bc_request);
 
diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index 416ce42..44c2d23 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -1052,7 +1052,7 @@ found:
 	kref_init(&xprt->kref);
 	spin_lock_init(&xprt->transport_lock);
 	spin_lock_init(&xprt->reserve_lock);
-	rwlock_init(&xprt->bc_pa_lock);
+	spin_lock_init(&xprt->bc_pa_lock);
 
 	INIT_LIST_HEAD(&xprt->free);
 	INIT_LIST_HEAD(&xprt->recv);
-- 
1.5.3.3