[PATCH v2 1/2] NFS: finish_automount() requires us to hold 2 refs to the mount record

[PATCH v2 1/2] NFS: finish_automount() requires us to hold 2 refs to the mount record

[trondmy]

From: Trond Myklebust <trond.myklebust@hammerspace.com>

We must not return from nfs_d_automount() without holding 2 references
to the mount record. Doing so, will trigger the BUG() in finish_automount().
Also ensure that we don't try to reschedule the automount timer with
a negative or zero timeout value.

Fixes: 22a1ae9a93fb ("NFS: If nfs_mountpoint_expiry_timeout < 0, do not expire submounts")
Cc: stable@vger.kernel.org # v5.5+
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
---
 fs/nfs/namespace.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c
index da67820462f2..fe19ae280262 100644
--- a/fs/nfs/namespace.c
+++ b/fs/nfs/namespace.c
@@ -145,6 +145,7 @@ struct vfsmount *nfs_d_automount(struct path *path)
 	struct vfsmount *mnt = ERR_PTR(-ENOMEM);
 	struct nfs_server *server = NFS_SERVER(d_inode(path->dentry));
 	struct nfs_client *client = server->nfs_client;
+	int timeout = READ_ONCE(nfs_mountpoint_expiry_timeout);
 	int ret;
 
 	if (IS_ROOT(path->dentry))
@@ -190,12 +191,12 @@ struct vfsmount *nfs_d_automount(struct path *path)
 	if (IS_ERR(mnt))
 		goto out_fc;
 
-	if (nfs_mountpoint_expiry_timeout < 0)
+	mntget(mnt); /* prevent immediate expiration */
+	if (timeout <= 0)
 		goto out_fc;
 
-	mntget(mnt); /* prevent immediate expiration */
 	mnt_set_expiry(mnt, &nfs_automount_list);
-	schedule_delayed_work(&nfs_automount_task, nfs_mountpoint_expiry_timeout);
+	schedule_delayed_work(&nfs_automount_task, timeout);
 
 out_fc:
 	put_fs_context(fc);
@@ -233,10 +234,11 @@ const struct inode_operations nfs_referral_inode_operations = {
 static void nfs_expire_automounts(struct work_struct *work)
 {
 	struct list_head *list = &nfs_automount_list;
+	int timeout = READ_ONCE(nfs_mountpoint_expiry_timeout);
 
 	mark_mounts_for_expiry(list);
-	if (!list_empty(list))
-		schedule_delayed_work(&nfs_automount_task, nfs_mountpoint_expiry_timeout);
+	if (!list_empty(list) && timeout > 0)
+		schedule_delayed_work(&nfs_automount_task, timeout);
 }
 
 void nfs_release_automount_timer(void)
-- 
2.25.1

[PATCH v2 2/2] NFS: Add a module parameter to set nfs_mountpoint_expiry_timeout

[trondmy]

From: Trond Myklebust <trond.myklebust@hammerspace.com>

Setting nfs_mountpoint_expiry_timeout() to a negative value stops
mountpoint expiration, while setting it to a positive value restarts
the scheduler.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
---
 fs/nfs/namespace.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c
index fe19ae280262..6b063227e34e 100644
--- a/fs/nfs/namespace.c
+++ b/fs/nfs/namespace.c
@@ -311,3 +311,53 @@ int nfs_submount(struct fs_context *fc, struct nfs_server *server)
 	return nfs_do_submount(fc);
 }
 EXPORT_SYMBOL_GPL(nfs_submount);
+
+static int param_set_nfs_timeout(const char *val, const struct kernel_param *kp)
+{
+	long num;
+	int ret;
+
+	if (!val)
+		return -EINVAL;
+	ret = kstrtol(val, 0, &num);
+	if (ret)
+		return -EINVAL;
+	if (num > 0) {
+		if (num >= INT_MAX / HZ)
+			num = INT_MAX;
+		else
+			num *= HZ;
+		*((int *)kp->arg) = num;
+		if (!list_empty(&nfs_automount_list))
+			mod_delayed_work(system_wq, &nfs_automount_task, num);
+	} else {
+		*((int *)kp->arg) = -1*HZ;
+		cancel_delayed_work(&nfs_automount_task);
+	}
+	return 0;
+}
+
+static int param_get_nfs_timeout(char *buffer, const struct kernel_param *kp)
+{
+	long num = *((int *)kp->arg);
+
+	if (num > 0) {
+		if (num >= INT_MAX - (HZ - 1))
+			num = INT_MAX / HZ;
+		else
+			num = (num + (HZ - 1)) / HZ;
+	} else
+		num = -1;
+	return scnprintf(buffer, PAGE_SIZE, "%li\n", num);
+}
+
+static const struct kernel_param_ops param_ops_nfs_timeout = {
+	.set = param_set_nfs_timeout,
+	.get = param_get_nfs_timeout,
+};
+#define param_check_nfs_timeout(name, p) __param_check(name, p, int);
+
+module_param(nfs_mountpoint_expiry_timeout, nfs_timeout, 0644);
+MODULE_PARM_DESC(nfs_mountpoint_expiry_timeout,
+		"Set the NFS automounted mountpoint timeout value (seconds)."
+		"Values <= 0 turn expiration off.");
-- 
2.25.1