sunrpc: fix potential races in pool_stats collection

In a later patch, we'll be removing some spinlocking around the socket
and thread queueing code in order to fix some contention problems. At
that point, the stats counters will no longer be protected by the
sp_lock.

Change the counters to atomic_long_t fields, except for the
"sockets_queued" counter which will still be manipulated under a
spinlock.

Signed-off-by: Jeff Layton <jlayton@primarydata.com>
Tested-by: Chris Worley <chris.worley@primarydata.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

include/linux/sunrpc/svc.h

@@ -26,10 +26,10 @@ typedef int		(*svc_thread_fn)(void *);
 
 /* statistics for svc_pool structures */
 struct svc_pool_stats {
-	unsigned long	packets;
+	atomic_long_t	packets;
 	unsigned long	sockets_queued;
-	unsigned long	threads_woken;
-	unsigned long	threads_timedout;
+	atomic_long_t	threads_woken;
+	atomic_long_t	threads_timedout;
 };
 
 /*

net/sunrpc/svc_xprt.c

@@ -362,7 +362,7 @@ static void svc_xprt_do_enqueue(struct svc_xprt *xprt)
 	pool = svc_pool_for_cpu(xprt->xpt_server, cpu);
 	spin_lock_bh(&pool->sp_lock);
 
-	pool->sp_stats.packets++;
+	atomic_long_inc(&pool->sp_stats.packets);
 
 	if (!list_empty(&pool->sp_threads)) {
 		rqstp = list_entry(pool->sp_threads.next,
@@ -383,7 +383,7 @@ static void svc_xprt_do_enqueue(struct svc_xprt *xprt)
 		svc_xprt_get(xprt);
 		wake_up_process(rqstp->rq_task);
 		rqstp->rq_xprt = xprt;
-		pool->sp_stats.threads_woken++;
+		atomic_long_inc(&pool->sp_stats.threads_woken);
 	} else {
 		dprintk("svc: transport %p put into queue\n", xprt);
 		list_add_tail(&xprt->xpt_ready, &pool->sp_sockets);
@@ -669,7 +669,7 @@ static struct svc_xprt *svc_get_next_xprt(struct svc_rqst *rqstp, long timeout)
 
 		spin_lock_bh(&pool->sp_lock);
 		if (!time_left)
-			pool->sp_stats.threads_timedout++;
+			atomic_long_inc(&pool->sp_stats.threads_timedout);
 
 		xprt = rqstp->rq_xprt;
 		if (!xprt) {
@@ -1306,10 +1306,10 @@ static int svc_pool_stats_show(struct seq_file *m, void *p)
 
 	seq_printf(m, "%u %lu %lu %lu %lu\n",
 		pool->sp_id,
-		pool->sp_stats.packets,
+		(unsigned long)atomic_long_read(&pool->sp_stats.packets),
 		pool->sp_stats.sockets_queued,
-		pool->sp_stats.threads_woken,
-		pool->sp_stats.threads_timedout);
+		(unsigned long)atomic_long_read(&pool->sp_stats.threads_woken),
+		(unsigned long)atomic_long_read(&pool->sp_stats.threads_timedout));
 
 	return 0;
 }