[PATCH 2/2] ceph: quota: fix quota subdir mounts

[Luis Henriques]

The CephFS kernel client does not enforce quotas set in a directory that isn't
visible from the mount point.  For example, given the path '/dir1/dir2', if quotas
are set in 'dir1' and the filesystem is mounted with

  mount -t ceph <server>:<port>:/dir1/ /mnt

then the client won't be able to access 'dir1' inode, even if 'dir2' belongs to
a quota realm that points to it.

This patch fixes this issue by simply doing an MDS LOOKUPINO operation for
unknown inodes.  Any inode reference obtained this way will be added to a list
in ceph_mds_client, and will only be released when the filesystem is umounted.

Link: https://tracker.ceph.com/issues/38482
Reported-by: Hendrik Peyerl <hpeyerl@xxxxxxxxxxxx>
Signed-off-by: Luis Henriques <lhenriques@xxxxxxxx>
---
 fs/ceph/mds_client.c | 14 +++++++
 fs/ceph/mds_client.h |  2 +
 fs/ceph/quota.c      | 91 +++++++++++++++++++++++++++++++++++++++-----
 fs/ceph/super.h      |  2 +
 4 files changed, 99 insertions(+), 10 deletions(-)

diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 163fc74bf221..72c5ce5e4209 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -3656,6 +3656,8 @@ int ceph_mdsc_init(struct ceph_fs_client *fsc)
 	mdsc->max_sessions = 0;
 	mdsc->stopping = 0;
 	atomic64_set(&mdsc->quotarealms_count, 0);
+	INIT_LIST_HEAD(&mdsc->quotarealms_inodes_list);
+	spin_lock_init(&mdsc->quotarealms_inodes_lock);
 	mdsc->last_snap_seq = 0;
 	init_rwsem(&mdsc->snap_rwsem);
 	mdsc->snap_realms = RB_ROOT;
@@ -3726,9 +3728,21 @@ static void wait_requests(struct ceph_mds_client *mdsc)
  */
 void ceph_mdsc_pre_umount(struct ceph_mds_client *mdsc)
 {
+	struct ceph_inode_info *ci;
+
 	dout("pre_umount\n");
 	mdsc->stopping = 1;
 
+	spin_lock(&mdsc->quotarealms_inodes_lock);
+	while(!list_empty(&mdsc->quotarealms_inodes_list)) {
+		ci = list_first_entry(&mdsc->quotarealms_inodes_list,
+				      struct ceph_inode_info,
+				      i_quotarealms_inode_item);
+		list_del(&ci->i_quotarealms_inode_item);
+		iput(&ci->vfs_inode);
+	}
+	spin_unlock(&mdsc->quotarealms_inodes_lock);
+
 	lock_unlock_sessions(mdsc);
 	ceph_flush_dirty_caps(mdsc);
 	wait_requests(mdsc);
diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
index 729da155ebf0..58968fb338ec 100644
--- a/fs/ceph/mds_client.h
+++ b/fs/ceph/mds_client.h
@@ -329,6 +329,8 @@ struct ceph_mds_client {
 	int                     stopping;      /* true if shutting down */
 
 	atomic64_t		quotarealms_count; /* # realms with quota */
+	struct list_head	quotarealms_inodes_list;
+	spinlock_t		quotarealms_inodes_lock;
 
 	/*
 	 * snap_rwsem will cover cap linkage into snaprealms, and
diff --git a/fs/ceph/quota.c b/fs/ceph/quota.c
index 9455d3aef0c3..c57c0b709efe 100644
--- a/fs/ceph/quota.c
+++ b/fs/ceph/quota.c
@@ -22,7 +22,16 @@ void ceph_adjust_quota_realms_count(struct inode *inode, bool inc)
 static inline bool ceph_has_realms_with_quotas(struct inode *inode)
 {
 	struct ceph_mds_client *mdsc = ceph_inode_to_client(inode)->mdsc;
-	return atomic64_read(&mdsc->quotarealms_count) > 0;
+	struct super_block *sb = mdsc->fsc->sb;
+
+	if (atomic64_read(&mdsc->quotarealms_count) > 0)
+		return true;
+	/* if root is the real CephFS root, we don't have quota realms */
+	if (sb->s_root->d_inode &&
+	    (sb->s_root->d_inode->i_ino == CEPH_INO_ROOT))
+		return false;
+	/* otherwise, we can't know for sure */
+	return true;
 }
 
 void ceph_handle_quota(struct ceph_mds_client *mdsc,
@@ -68,6 +77,37 @@ void ceph_handle_quota(struct ceph_mds_client *mdsc,
 	iput(inode);
 }
 
+/*
+ * This function will try to lookup a realm inode.  If the inode is found
+ * (through an MDS LOOKUPINO operation), the realm->inode will be updated and
+ * the inode will also be added to an mdsc list which will be freed only when
+ * the filesystem is umounted.
+ */
+static struct inode *lookup_quotarealm_inode(struct ceph_mds_client *mdsc,
+					     struct super_block *sb,
+					     struct ceph_snap_realm *realm)
+{
+	struct inode *in;
+
+	in = ceph_lookup_inode(sb, realm->ino);
+	if (IS_ERR(in)) {
+		pr_warn("Can't lookup inode %llx (err: %ld)\n",
+			realm->ino, PTR_ERR(in));
+		return in;
+	}
+
+	spin_lock(&mdsc->quotarealms_inodes_lock);
+	list_add(&ceph_inode(in)->i_quotarealms_inode_item,
+		 &mdsc->quotarealms_inodes_list);
+	spin_unlock(&mdsc->quotarealms_inodes_lock);
+
+	spin_lock(&realm->inodes_with_caps_lock);
+	realm->inode = in;
+	spin_unlock(&realm->inodes_with_caps_lock);
+
+	return in;
+}
+
 /*
  * This function walks through the snaprealm for an inode and returns the
  * ceph_snap_realm for the first snaprealm that has quotas set (either max_files
@@ -76,9 +116,15 @@ void ceph_handle_quota(struct ceph_mds_client *mdsc,
  *
  * Note that the caller is responsible for calling ceph_put_snap_realm() on the
  * returned realm.
+ *
+ * Callers of this function need to hold mdsc->snap_rwsem.  If there's the need
+ * to do an inode lookup, this rwsem will be temporarily dropped.  Hence the
+ * 'retry' argument: if rwsem needs to be dropped and 'retry' is 'true' this
+ * function will return -EAGAIN; otherwise, the whole operation will be
+ * restarted.
  */
 static struct ceph_snap_realm *get_quota_realm(struct ceph_mds_client *mdsc,
-					       struct inode *inode)
+					       struct inode *inode, bool retry)
 {
 	struct ceph_inode_info *ci = NULL;
 	struct ceph_snap_realm *realm, *next;
@@ -88,6 +134,7 @@ static struct ceph_snap_realm *get_quota_realm(struct ceph_mds_client *mdsc,
 	if (ceph_snap(inode) != CEPH_NOSNAP)
 		return NULL;
 
+restart:
 	realm = ceph_inode(inode)->i_snap_realm;
 	if (realm)
 		ceph_get_snap_realm(mdsc, realm);
@@ -98,8 +145,17 @@ static struct ceph_snap_realm *get_quota_realm(struct ceph_mds_client *mdsc,
 		spin_lock(&realm->inodes_with_caps_lock);
 		in = realm->inode ? igrab(realm->inode) : NULL;
 		spin_unlock(&realm->inodes_with_caps_lock);
-		if (!in)
-			break;
+		if (!in) {
+			up_read(&mdsc->snap_rwsem);
+			in = lookup_quotarealm_inode(mdsc, inode->i_sb, realm);
+			down_read(&mdsc->snap_rwsem);
+			if (IS_ERR(in))
+				break;
+			ceph_put_snap_realm(mdsc, realm);
+			if (!retry)
+				return ERR_PTR(-EAGAIN);
+			goto restart;
+		}
 
 		ci = ceph_inode(in);
 		has_quota = __ceph_has_any_quota(ci);
@@ -125,9 +181,17 @@ bool ceph_quota_is_same_realm(struct inode *old, struct inode *new)
 	struct ceph_snap_realm *old_realm, *new_realm;
 	bool is_same;
 
+restart:
 	down_read(&mdsc->snap_rwsem);
-	old_realm = get_quota_realm(mdsc, old);
-	new_realm = get_quota_realm(mdsc, new);
+	old_realm = get_quota_realm(mdsc, old, true);
+	/* This needs to be atomic, so we need to hold snap_rwsem */
+	new_realm = get_quota_realm(mdsc, new, false);
+	if (PTR_ERR(new_realm) == -EAGAIN) {
+		up_read(&mdsc->snap_rwsem);
+		if (old_realm)
+			ceph_put_snap_realm(mdsc, old_realm);
+		goto restart;
+	}
 	is_same = (old_realm == new_realm);
 	up_read(&mdsc->snap_rwsem);
 
@@ -166,6 +230,7 @@ static bool check_quota_exceeded(struct inode *inode, enum quota_check_op op,
 		return false;
 
 	down_read(&mdsc->snap_rwsem);
+restart:
 	realm = ceph_inode(inode)->i_snap_realm;
 	if (realm)
 		ceph_get_snap_realm(mdsc, realm);
@@ -176,9 +241,15 @@ static bool check_quota_exceeded(struct inode *inode, enum quota_check_op op,
 		spin_lock(&realm->inodes_with_caps_lock);
 		in = realm->inode ? igrab(realm->inode) : NULL;
 		spin_unlock(&realm->inodes_with_caps_lock);
-		if (!in)
-			break;
-
+		if (!in) {
+			up_read(&mdsc->snap_rwsem);
+			in = lookup_quotarealm_inode(mdsc, inode->i_sb, realm);
+			down_read(&mdsc->snap_rwsem);
+			if (IS_ERR(in))
+				break;
+			ceph_put_snap_realm(mdsc, realm);
+			goto restart;
+		}
 		ci = ceph_inode(in);
 		spin_lock(&ci->i_ceph_lock);
 		if (op == QUOTA_CHECK_MAX_FILES_OP) {
@@ -314,7 +385,7 @@ bool ceph_quota_update_statfs(struct ceph_fs_client *fsc, struct kstatfs *buf)
 	bool is_updated = false;
 
 	down_read(&mdsc->snap_rwsem);
-	realm = get_quota_realm(mdsc, d_inode(fsc->sb->s_root));
+	realm = get_quota_realm(mdsc, d_inode(fsc->sb->s_root), true);
 	up_read(&mdsc->snap_rwsem);
 	if (!realm)
 		return false;
diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index ce51e98b08ec..cc7766aeb73b 100644
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -375,6 +375,8 @@ struct ceph_inode_info {
 	struct list_head i_snap_realm_item;
 	struct list_head i_snap_flush_item;
 
+	struct list_head i_quotarealms_inode_item;
+
 	struct work_struct i_wb_work;  /* writeback work */
 	struct work_struct i_pg_inv_work;  /* page invalidation work */