NFSD: Fix frame size warning in svc_export_parse()

fs/nfsd/export.c: In function 'svc_export_parse':
fs/nfsd/export.c:737:1: warning: the frame size of 1040 bytes is larger than 1024 bytes [-Wframe-larger-than=]
    737 | }

On my systems, svc_export_parse() has a stack frame of over 800
bytes, not 1040, but nonetheless, it could do with some reduction.

When a struct svc_export is on the stack, it's a temporary structure
used as an argument, and not visible as an actual exported FS. No
need to reserve space for export_stats in such cases.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202310012359.YEw5IrK6-lkp@intel.com/
Cc: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/export.c

@@ -339,12 +339,16 @@ static int export_stats_init(struct export_stats *stats)
 
 static void export_stats_reset(struct export_stats *stats)
 {
-	nfsd_percpu_counters_reset(stats->counter, EXP_STATS_COUNTERS_NUM);
+	if (stats)
+		nfsd_percpu_counters_reset(stats->counter,
+					   EXP_STATS_COUNTERS_NUM);
 }
 
 static void export_stats_destroy(struct export_stats *stats)
 {
-	nfsd_percpu_counters_destroy(stats->counter, EXP_STATS_COUNTERS_NUM);
+	if (stats)
+		nfsd_percpu_counters_destroy(stats->counter,
+					     EXP_STATS_COUNTERS_NUM);
 }
 
 static void svc_export_put(struct kref *ref)
@@ -353,7 +357,8 @@ static void svc_export_put(struct kref *ref)
 	path_put(&exp->ex_path);
 	auth_domain_put(exp->ex_client);
 	nfsd4_fslocs_free(&exp->ex_fslocs);
-	export_stats_destroy(&exp->ex_stats);
+	export_stats_destroy(exp->ex_stats);
+	kfree(exp->ex_stats);
 	kfree(exp->ex_uuid);
 	kfree_rcu(exp, ex_rcu);
 }
@@ -767,13 +772,15 @@ static int svc_export_show(struct seq_file *m,
 	seq_putc(m, '\t');
 	seq_escape(m, exp->ex_client->name, " \t\n\\");
 	if (export_stats) {
-		seq_printf(m, "\t%lld\n", exp->ex_stats.start_time);
+		struct percpu_counter *counter = exp->ex_stats->counter;
+
+		seq_printf(m, "\t%lld\n", exp->ex_stats->start_time);
 		seq_printf(m, "\tfh_stale: %lld\n",
-			   percpu_counter_sum_positive(&exp->ex_stats.counter[EXP_STATS_FH_STALE]));
+			   percpu_counter_sum_positive(&counter[EXP_STATS_FH_STALE]));
 		seq_printf(m, "\tio_read: %lld\n",
-			   percpu_counter_sum_positive(&exp->ex_stats.counter[EXP_STATS_IO_READ]));
+			   percpu_counter_sum_positive(&counter[EXP_STATS_IO_READ]));
 		seq_printf(m, "\tio_write: %lld\n",
-			   percpu_counter_sum_positive(&exp->ex_stats.counter[EXP_STATS_IO_WRITE]));
+			   percpu_counter_sum_positive(&counter[EXP_STATS_IO_WRITE]));
 		seq_putc(m, '\n');
 		return 0;
 	}
@@ -819,7 +826,7 @@ static void svc_export_init(struct cache_head *cnew, struct cache_head *citem)
 	new->ex_layout_types = 0;
 	new->ex_uuid = NULL;
 	new->cd = item->cd;
-	export_stats_reset(&new->ex_stats);
+	export_stats_reset(new->ex_stats);
 }
 
 static void export_update(struct cache_head *cnew, struct cache_head *citem)
@@ -856,7 +863,14 @@ static struct cache_head *svc_export_alloc(void)
 	if (!i)
 		return NULL;
 
-	if (export_stats_init(&i->ex_stats)) {
+	i->ex_stats = kmalloc(sizeof(*(i->ex_stats)), GFP_KERNEL);
+	if (!i->ex_stats) {
+		kfree(i);
+		return NULL;
+	}
+
+	if (export_stats_init(i->ex_stats)) {
+		kfree(i->ex_stats);
 		kfree(i);
 		return NULL;
 	}

fs/nfsd/export.h

@@ -64,10 +64,10 @@ struct svc_export {
 	struct cache_head	h;
 	struct auth_domain *	ex_client;
 	int			ex_flags;
+	int			ex_fsid;
 	struct path		ex_path;
 	kuid_t			ex_anon_uid;
 	kgid_t			ex_anon_gid;
-	int			ex_fsid;
 	unsigned char *		ex_uuid; /* 16 byte fsid */
 	struct nfsd4_fs_locations ex_fslocs;
 	uint32_t		ex_nflavors;
@@ -76,8 +76,8 @@ struct svc_export {
 	struct nfsd4_deviceid_map *ex_devid_map;
 	struct cache_detail	*cd;
 	struct rcu_head		ex_rcu;
-	struct export_stats	ex_stats;
 	unsigned long		ex_xprtsec_modes;
+	struct export_stats	*ex_stats;
 };
 
 /* an "export key" (expkey) maps a filehandlefragement to an

fs/nfsd/stats.h

@@ -61,22 +61,22 @@ static inline void nfsd_stats_rc_nocache_inc(void)
 static inline void nfsd_stats_fh_stale_inc(struct svc_export *exp)
 {
 	percpu_counter_inc(&nfsdstats.counter[NFSD_STATS_FH_STALE]);
-	if (exp)
-		percpu_counter_inc(&exp->ex_stats.counter[EXP_STATS_FH_STALE]);
+	if (exp && exp->ex_stats)
+		percpu_counter_inc(&exp->ex_stats->counter[EXP_STATS_FH_STALE]);
 }
 
 static inline void nfsd_stats_io_read_add(struct svc_export *exp, s64 amount)
 {
 	percpu_counter_add(&nfsdstats.counter[NFSD_STATS_IO_READ], amount);
-	if (exp)
-		percpu_counter_add(&exp->ex_stats.counter[EXP_STATS_IO_READ], amount);
+	if (exp && exp->ex_stats)
+		percpu_counter_add(&exp->ex_stats->counter[EXP_STATS_IO_READ], amount);
 }
 
 static inline void nfsd_stats_io_write_add(struct svc_export *exp, s64 amount)
 {
 	percpu_counter_add(&nfsdstats.counter[NFSD_STATS_IO_WRITE], amount);
-	if (exp)
-		percpu_counter_add(&exp->ex_stats.counter[EXP_STATS_IO_WRITE], amount);
+	if (exp && exp->ex_stats)
+		percpu_counter_add(&exp->ex_stats->counter[EXP_STATS_IO_WRITE], amount);
 }
 
 static inline void nfsd_stats_payload_misses_inc(struct nfsd_net *nn)