nfsd: Revert "nfsd: release svc_expkey/svc_export with rcu_work"

This reverts commit f8c989a.

Before this commit, svc_export_put or expkey_put will call path_put with
sync mode. After this commit, path_put will be called with async mode.
And this can lead the unexpected results show as follow.

mkfs.xfs -f /dev/sda
echo "/ *(rw,no_root_squash,fsid=0)" > /etc/exports
echo "/mnt *(rw,no_root_squash,fsid=1)" >> /etc/exports
exportfs -ra
service nfs-server start
mount -t nfs -o vers=4.0 127.0.0.1:/mnt /mnt1
mount /dev/sda /mnt/sda
touch /mnt1/sda/file
exportfs -r
umount /mnt/sda # failed unexcepted

The touch will finally call nfsd_cross_mnt, add refcount to mount, and
then add cache_head. Before this commit, exportfs -r will call
cache_flush to cleanup all cache_head, and path_put in
svc_export_put/expkey_put will be finished with sync mode. So, the
latter umount will always success. However, after this commit, path_put
will be called with async mode, the latter umount may failed, and if
we add some delay, umount will success too. Personally I think this bug
and should be fixed. We first revert before bugfix patch, and then fix
the original bug with a different way.

Fixes: f8c989a ("nfsd: release svc_expkey/svc_export with rcu_work")
Signed-off-by: Yang Erkun <yangerkun@huawei.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/export.c

@@ -40,24 +40,15 @@
 #define	EXPKEY_HASHMAX		(1 << EXPKEY_HASHBITS)
 #define	EXPKEY_HASHMASK		(EXPKEY_HASHMAX -1)
 
-static void expkey_put_work(struct work_struct *work)
+static void expkey_put(struct kref *ref)
 {
-	struct svc_expkey *key =
-		container_of(to_rcu_work(work), struct svc_expkey, ek_rcu_work);
+	struct svc_expkey *key = container_of(ref, struct svc_expkey, h.ref);
 
 	if (test_bit(CACHE_VALID, &key->h.flags) &&
 	    !test_bit(CACHE_NEGATIVE, &key->h.flags))
 		path_put(&key->ek_path);
 	auth_domain_put(key->ek_client);
-	kfree(key);
-}
-
-static void expkey_put(struct kref *ref)
-{
-	struct svc_expkey *key = container_of(ref, struct svc_expkey, h.ref);
-
-	INIT_RCU_WORK(&key->ek_rcu_work, expkey_put_work);
-	queue_rcu_work(system_wq, &key->ek_rcu_work);
+	kfree_rcu(key, ek_rcu);
 }
 
 static int expkey_upcall(struct cache_detail *cd, struct cache_head *h)
@@ -364,26 +355,16 @@ static void export_stats_destroy(struct export_stats *stats)
 					    EXP_STATS_COUNTERS_NUM);
 }
 
-static void svc_export_put_work(struct work_struct *work)
+static void svc_export_put(struct kref *ref)
 {
-	struct svc_export *exp =
-		container_of(to_rcu_work(work), struct svc_export, ex_rcu_work);
-
+	struct svc_export *exp = container_of(ref, struct svc_export, h.ref);
 	path_put(&exp->ex_path);
 	auth_domain_put(exp->ex_client);
 	nfsd4_fslocs_free(&exp->ex_fslocs);
 	export_stats_destroy(exp->ex_stats);
 	kfree(exp->ex_stats);
 	kfree(exp->ex_uuid);
-	kfree(exp);
-}
-
-static void svc_export_put(struct kref *ref)
-{
-	struct svc_export *exp = container_of(ref, struct svc_export, h.ref);
-
-	INIT_RCU_WORK(&exp->ex_rcu_work, svc_export_put_work);
-	queue_rcu_work(system_wq, &exp->ex_rcu_work);
+	kfree_rcu(exp, ex_rcu);
 }
 
 static int svc_export_upcall(struct cache_detail *cd, struct cache_head *h)

fs/nfsd/export.h

@@ -75,7 +75,7 @@ struct svc_export {
 	u32			ex_layout_types;
 	struct nfsd4_deviceid_map *ex_devid_map;
 	struct cache_detail	*cd;
-	struct rcu_work		ex_rcu_work;
+	struct rcu_head		ex_rcu;
 	unsigned long		ex_xprtsec_modes;
 	struct export_stats	*ex_stats;
 };
@@ -92,7 +92,7 @@ struct svc_expkey {
 	u32			ek_fsid[6];
 
 	struct path		ek_path;
-	struct rcu_work		ek_rcu_work;
+	struct rcu_head		ek_rcu;
 };
 
 #define EX_ISSYNC(exp)		(!((exp)->ex_flags & NFSEXP_ASYNC))