ceph: document unlocked d_parent accesses

For the most part we don't care about racing with rename when directing
MDS requests; either the old or new parent is fine.  Document that, and
do some minor cleanup.

Reviewed-by: Yehuda Sadeh <yehuda@hq.newdream.net>
Signed-off-by: Sage Weil <sage@newdream.net>

diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
index 7263f825d426daac2861e123c297bdac8d951c26..852ff8600ac9875a5acf896247fb92485d6a8848 100644 (file)
--- a/fs/ceph/dir.c
+++ b/fs/ceph/dir.c
@@ -506,7 +506,7 @@ int ceph_handle_snapdir(struct ceph_mds_request *req,
                        struct dentry *dentry, int err)
 {
        struct ceph_fs_client *fsc = ceph_sb_to_client(dentry->d_sb);
-       struct inode *parent = dentry->d_parent->d_inode;
+       struct inode *parent = dentry->d_parent->d_inode; /* we hold i_mutex */
 
        /* .snap dir? */
        if (err == -ENOENT &&

diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 66a8939cc518bdd219ef6ae7df3b555f53b5604c..fee028b5332e0d802b26fdc94dab21057b41028a 100644 (file)
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -621,6 +621,12 @@ static void __unregister_request(struct ceph_mds_client *mdsc,
  */
 struct dentry *get_nonsnap_parent(struct dentry *dentry)
 {
+       /*
+        * we don't need to worry about protecting the d_parent access
+        * here because we never renaming inside the snapped namespace
+        * except to resplice to another snapdir, and either the old or new
+        * result is a valid result.
+        */
        while (!IS_ROOT(dentry) && ceph_snap(dentry->d_inode) != CEPH_NOSNAP)
                dentry = dentry->d_parent;
        return dentry;
@@ -656,7 +662,9 @@ static int __choose_mds(struct ceph_mds_client *mdsc,
        if (req->r_inode) {
                inode = req->r_inode;
        } else if (req->r_dentry) {
-               struct inode *dir = req->r_dentry->d_parent->d_inode;
+               /* ignore race with rename; old or new d_parent is okay */
+               struct dentry *parent = req->r_dentry->d_parent;
+               struct inode *dir = parent->d_inode;
 
                if (dir->i_sb != mdsc->fsc->sb) {
                        /* not this fs! */
@@ -664,8 +672,7 @@ static int __choose_mds(struct ceph_mds_client *mdsc,
                } else if (ceph_snap(dir) != CEPH_NOSNAP) {
                        /* direct snapped/virtual snapdir requests
                         * based on parent dir inode */
-                       struct dentry *dn =
-                               get_nonsnap_parent(req->r_dentry->d_parent);
+                       struct dentry *dn = get_nonsnap_parent(parent);
                        inode = dn->d_inode;
                        dout("__choose_mds using nonsnap parent %p\n", inode);
                } else if (req->r_dentry->d_inode) {