[PATCH] nfsd: move init of percpu reply_cache_stats counters back to nfsd_init_net

[Jeff Layton]

f5f9d4a314da moved the initialization of the reply cache into the nfsd
startup, but it didn't account for the stats counters which can be
accessed before nfsd is ever started, causing a NULL pointer
dereference.

This is easy to trigger on some arches (like aarch64), but on x86_64,
calling this_cpu_ptr(NULL) evidently returns a pointer to the
fixed_percpu_data, which I guess this looks just enough like a newly
initialized percpu var to allow nfsd_reply_cache_stats_show to access it
without Oopsing.

Move the initialization of the per-net+per-cpu reply-cache counters back
into nfsd_init_net, while leaving the rest of the reply cache
allocations to be done at nfsd startup time.

Kudos to Eirik who did most of the legwork to track this down.

Cc: stable@xxxxxxxxxxxxxxx # v6.3+
Fixes: f5f9d4a314da ("nfsd: move reply cache initialization into nfsd startup")
Reported-and-Tested-by: Eirik Fuller <efuller@xxxxxxxxxx>
Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
---
 fs/nfsd/cache.h    |  2 ++
 fs/nfsd/nfscache.c | 13 +++----------
 fs/nfsd/nfsctl.c   |  8 ++++++++
 3 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/fs/nfsd/cache.h b/fs/nfsd/cache.h
index f21259ead64b..a4b12d6c41d3 100644
--- a/fs/nfsd/cache.h
+++ b/fs/nfsd/cache.h
@@ -80,6 +80,8 @@ enum {
 
 int	nfsd_drc_slab_create(void);
 void	nfsd_drc_slab_free(void);
+int	nfsd_reply_cache_stats_init(struct nfsd_net *nn);
+void	nfsd_reply_cache_stats_destroy(struct nfsd_net *nn);
 int	nfsd_reply_cache_init(struct nfsd_net *);
 void	nfsd_reply_cache_shutdown(struct nfsd_net *);
 int	nfsd_cache_lookup(struct svc_rqst *);
diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c
index 041faa13b852..b696dc629c0b 100644
--- a/fs/nfsd/nfscache.c
+++ b/fs/nfsd/nfscache.c
@@ -148,12 +148,12 @@ void nfsd_drc_slab_free(void)
 	kmem_cache_destroy(drc_slab);
 }
 
-static int nfsd_reply_cache_stats_init(struct nfsd_net *nn)
+int nfsd_reply_cache_stats_init(struct nfsd_net *nn)
 {
 	return nfsd_percpu_counters_init(nn->counter, NFSD_NET_COUNTERS_NUM);
 }
 
-static void nfsd_reply_cache_stats_destroy(struct nfsd_net *nn)
+void nfsd_reply_cache_stats_destroy(struct nfsd_net *nn)
 {
 	nfsd_percpu_counters_destroy(nn->counter, NFSD_NET_COUNTERS_NUM);
 }
@@ -169,17 +169,13 @@ int nfsd_reply_cache_init(struct nfsd_net *nn)
 	hashsize = nfsd_hashsize(nn->max_drc_entries);
 	nn->maskbits = ilog2(hashsize);
 
-	status = nfsd_reply_cache_stats_init(nn);
-	if (status)
-		goto out_nomem;
-
 	nn->nfsd_reply_cache_shrinker.scan_objects = nfsd_reply_cache_scan;
 	nn->nfsd_reply_cache_shrinker.count_objects = nfsd_reply_cache_count;
 	nn->nfsd_reply_cache_shrinker.seeks = 1;
 	status = register_shrinker(&nn->nfsd_reply_cache_shrinker,
 				   "nfsd-reply:%s", nn->nfsd_name);
 	if (status)
-		goto out_stats_destroy;
+		return status;
 
 	nn->drc_hashtbl = kvzalloc(array_size(hashsize,
 				sizeof(*nn->drc_hashtbl)), GFP_KERNEL);
@@ -195,9 +191,6 @@ int nfsd_reply_cache_init(struct nfsd_net *nn)
 	return 0;
 out_shrinker:
 	unregister_shrinker(&nn->nfsd_reply_cache_shrinker);
-out_stats_destroy:
-	nfsd_reply_cache_stats_destroy(nn);
-out_nomem:
 	printk(KERN_ERR "nfsd: failed to allocate reply cache\n");
 	return -ENOMEM;
 }
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 1489e0b703b4..7c837afcf615 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1505,6 +1505,9 @@ static __net_init int nfsd_init_net(struct net *net)
 	retval = nfsd_idmap_init(net);
 	if (retval)
 		goto out_idmap_error;
+	retval = nfsd_reply_cache_stats_init(nn);
+	if (retval)
+		goto out_repcache_error;
 	nn->nfsd_versions = NULL;
 	nn->nfsd4_minorversions = NULL;
 	nfsd4_init_leases_net(nn);
@@ -1513,6 +1516,8 @@ static __net_init int nfsd_init_net(struct net *net)
 
 	return 0;
 
+out_repcache_error:
+	nfsd_idmap_shutdown(net);
 out_idmap_error:
 	nfsd_export_shutdown(net);
 out_export_error:
@@ -1521,6 +1526,9 @@ static __net_init int nfsd_init_net(struct net *net)
 
 static __net_exit void nfsd_exit_net(struct net *net)
 {
+	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+
+	nfsd_reply_cache_stats_destroy(nn);
 	nfsd_idmap_shutdown(net);
 	nfsd_export_shutdown(net);
 	nfsd_netns_free_versions(net_generic(net, nfsd_net_id));
-- 
2.40.1