[PATCH v2 1/2] ceph: mark the superblock active after mounting

[Xiubo Li via B4 Relay]

From: Xiubo Li <xiubo.li@xxxxxxxxx>

ceph_get_tree() calls sget_fc() directly and so never goes through
vfs_get_super(), which is what sets SB_ACTIVE after fill_super for
filesystems that use it.  Before commit 82995cc6c5ae ("libceph, rbd,
ceph: convert to use the new mount API") the flag used to be set by
get_sb_nodev(), which did this for ceph, but the conversion dropped it.

SB_ACTIVE is required for iput_final() to retain an inode on the
inode LRU instead of evicting it once its last reference goes away.
This has gone unnoticed because ceph sets inode_just_drop() for
->drop_inode, which always asks for eviction, so the retain branch in
iput_final() was never reachable.  The next patch makes ->drop_inode()
able to retain inodes, and that needs the flag to actually work.

Set it once the mount is up, like nfs_get_tree() does.

Fixes: 82995cc6c5ae ("libceph, rbd, ceph: convert to use the new mount API")
Signed-off-by: Xiubo Li <xiubo.li@xxxxxxxxx>
---
 fs/ceph/super.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/ceph/super.c b/fs/ceph/super.c
index 518ee63d55fb..6573285d704a 100644
--- a/fs/ceph/super.c
+++ b/fs/ceph/super.c
@@ -1381,6 +1381,15 @@ static int ceph_get_tree(struct fs_context *fc)
 	doutc(fsc->client, "root %p inode %p ino %llx.%llx\n", res,
 		    d_inode(res), ceph_vinop(d_inode(res)));
 	fc->root = fsc->sb->s_root;
+
+	/*
+	 * The mount is up.  sget_fc() leaves SB_ACTIVE unset, and, unlike
+	 * filesystems that go through vfs_get_super(), nothing else sets
+	 * it here, so iput_final() would always evict an inode whose
+	 * ->drop_inode() asks to retain it.  Set it like nfs_get_tree()
+	 * does.
+	 */
+	sb->s_flags |= SB_ACTIVE;
 	return 0;
 
 out_splat:

-- 
2.53.0