ceph: don't use d_add in ceph_handle_snapdir

It's possible ceph_get_snapdir could end up finding a (disconnected)
inode that already exists in the cache. Change the prototype for
ceph_handle_snapdir to return a dentry pointer and have it use
d_splice_alias so we don't end up with an aliased dentry in the cache.

Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
index 3e57565..5624fae 100644 (file)
--- a/fs/ceph/dir.c
+++ b/fs/ceph/dir.c
@@ -667,8 +667,8 @@ out:
 /*
  * Handle lookups for the hidden .snap directory.
  */
-int ceph_handle_snapdir(struct ceph_mds_request *req,
-                       struct dentry *dentry, int err)
+struct dentry *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 = d_inode(dentry->d_parent); /* we hold i_mutex */
@@ -676,16 +676,17 @@ int ceph_handle_snapdir(struct ceph_mds_request *req,
        /* .snap dir? */
        if (err == -ENOENT &&
            ceph_snap(parent) == CEPH_NOSNAP &&
-           strcmp(dentry->d_name.name,
-                  fsc->mount_options->snapdir_name) == 0) {
+           strcmp(dentry->d_name.name, fsc->mount_options->snapdir_name) == 0) {
+               struct dentry *res;
                struct inode *inode = ceph_get_snapdir(parent);
-               dout("ENOENT on snapdir %p '%pd', linking to snapdir %p\n",
-                    dentry, dentry, inode);
-               BUG_ON(!d_unhashed(dentry));
-               d_add(dentry, inode);
-               err = 0;
+
+               res = d_splice_alias(inode, dentry);
+               dout("ENOENT on snapdir %p '%pd', linking to snapdir %p. Spliced dentry %p\n",
+                    dentry, dentry, inode, res);
+               if (res)
+                       dentry = res;
        }
-       return err;
+       return dentry;
 }
 
 /*
@@ -741,6 +742,7 @@ static struct dentry *ceph_lookup(struct inode *dir, struct dentry *dentry,
        struct ceph_fs_client *fsc = ceph_sb_to_client(dir->i_sb);
        struct ceph_mds_client *mdsc = ceph_sb_to_mdsc(dir->i_sb);
        struct ceph_mds_request *req;
+       struct dentry *res;
        int op;
        int mask;
        int err;
@@ -791,7 +793,13 @@ static struct dentry *ceph_lookup(struct inode *dir, struct dentry *dentry,
        req->r_parent = dir;
        set_bit(CEPH_MDS_R_PARENT_LOCKED, &req->r_req_flags);
        err = ceph_mdsc_do_request(mdsc, NULL, req);
-       err = ceph_handle_snapdir(req, dentry, err);
+       res = ceph_handle_snapdir(req, dentry, err);
+       if (IS_ERR(res)) {
+               err = PTR_ERR(res);
+       } else {
+               dentry = res;
+               err = 0;
+       }
        dentry = ceph_finish_lookup(req, dentry, err);
        ceph_mdsc_put_request(req);  /* will dput(dentry) */
        dout("lookup result=%p\n", dentry);

diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index 209535d..a6ef1d1 100644 (file)
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -739,9 +739,12 @@ retry:
        err = ceph_mdsc_do_request(mdsc,
                                   (flags & (O_CREAT|O_TRUNC)) ? dir : NULL,
                                   req);
-       err = ceph_handle_snapdir(req, dentry, err);
-       if (err)
+       dentry = ceph_handle_snapdir(req, dentry, err);
+       if (IS_ERR(dentry)) {
+               err = PTR_ERR(dentry);
                goto out_req;
+       }
+       err = 0;
 
        if ((flags & O_CREAT) && !req->r_reply_info.head->is_dentry)
                err = ceph_handle_notrace_create(dir, dentry);

diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index 188565d..07a3fb5 100644 (file)
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -1193,7 +1193,7 @@ extern const struct dentry_operations ceph_dentry_ops;
 
 extern loff_t ceph_make_fpos(unsigned high, unsigned off, bool hash_order);
 extern int ceph_handle_notrace_create(struct inode *dir, struct dentry *dentry);
-extern int ceph_handle_snapdir(struct ceph_mds_request *req,
+extern struct dentry *ceph_handle_snapdir(struct ceph_mds_request *req,
                               struct dentry *dentry, int err);
 extern struct dentry *ceph_finish_lookup(struct ceph_mds_request *req,
                                         struct dentry *dentry, int err);