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 7263f82..852ff86 100644
--- a/fs/ceph/dir.c
+++ b/fs/ceph/dir.c
@@ -506,7 +506,7 @@
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 66a8939..fee028b 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -621,6 +621,12 @@
*/
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 @@
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 @@
} 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) {
