fs/9p: Prevent parallel rename when doing fid_lookup

During fid lookup we need to make sure that the dentry->d_parent doesn't
change so that we can safely walk the parent dentries. To ensure that
we need to prevent cross directory rename during fid_lookup. Add a
per superblock rename_sem rw_semaphore to prevent parallel fid lookup and
rename.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

5 files changed, 91 insertions, 39 deletions

diff --git a/fs/9p/fid.c b/fs/9p/fid.c
index 5d6cfcbf73e7..358563689064 100644
--- a/fs/9p/fid.c
+++ b/fs/9p/fid.c
@@ -97,6 +97,34 @@ static struct p9_fid *v9fs_fid_find(struct dentry *dentry, u32 uid, int any)
         return ret;
 }
 
+/*
+ * We need to hold v9ses->rename_sem as long as we hold references
+ * to returned path array. Array element contain pointers to
+ * dentry names.
+ */
+static int build_path_from_dentry(struct v9fs_session_info *v9ses,
+                                  struct dentry *dentry, char ***names)
+{
+        int n = 0, i;
+        char **wnames;
+        struct dentry *ds;
+
+        for (ds = dentry; !IS_ROOT(ds); ds = ds->d_parent)
+                n++;
+
+        wnames = kmalloc(sizeof(char *) * n, GFP_KERNEL);
+        if (!wnames)
+                goto err_out;
+
+        for (ds = dentry, i = (n-1); i >= 0; i--, ds = ds->d_parent)
+                wnames[i] = (char  *)ds->d_name.name;
+
+        *names = wnames;
+        return n;
+err_out:
+        return -ENOMEM;
+}
+
 /**
  * v9fs_fid_lookup - lookup for a fid, try to walk if not found
  * @dentry: dentry to look for fid in
@@ -112,7 +140,7 @@ struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
         int i, n, l, clone, any, access;
         u32 uid;
         struct p9_fid *fid, *old_fid = NULL;
-        struct dentry *d, *ds;
+        struct dentry *ds;
         struct v9fs_session_info *v9ses;
         char **wnames, *uname;
 
@@ -139,50 +167,62 @@ struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
         fid = v9fs_fid_find(dentry, uid, any);
         if (fid)
                 return fid;
-
+        /*
+         * we don't have a matching fid. To do a TWALK we need
+         * parent fid. We need to prevent rename when we want to
+         * look at the parent.
+         */
+        down_read(&v9ses->rename_sem);
         ds = dentry->d_parent;
         fid = v9fs_fid_find(ds, uid, any);
-        if (!fid) { /* walk from the root */
-                n = 0;
-                for (ds = dentry; !IS_ROOT(ds); ds = ds->d_parent)
-                        n++;
-
-                fid = v9fs_fid_find(ds, uid, any);
-                if (!fid) { /* the user is not attached to the fs yet */
-                        if (access == V9FS_ACCESS_SINGLE)
-                                return ERR_PTR(-EPERM);
-
-                        if (v9fs_proto_dotu(v9ses) ||
-                                v9fs_proto_dotl(v9ses))
-                                uname = NULL;
-                        else
-                                uname = v9ses->uname;
+        if (fid) {
+                /* Found the parent fid do a lookup with that */
+                fid = p9_client_walk(fid, 1, (char **)&dentry->d_name.name, 1);
+                goto fid_out;
+        }
+        up_read(&v9ses->rename_sem);
 
-                        fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
-                                v9ses->aname);
+        /* start from the root and try to do a lookup */
+        fid = v9fs_fid_find(dentry->d_sb->s_root, uid, any);
+        if (!fid) {
+                /* the user is not attached to the fs yet */
+                if (access == V9FS_ACCESS_SINGLE)
+                        return ERR_PTR(-EPERM);
 
-                        if (IS_ERR(fid))
-                                return fid;
+                if (v9fs_proto_dotu(v9ses) || v9fs_proto_dotl(v9ses))
+                                uname = NULL;
+                else
+                        uname = v9ses->uname;
 
-                        v9fs_fid_add(ds, fid);
-                }
-        } else /* walk from the parent */
-                n = 1;
+                fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
+                                       v9ses->aname);
+                if (IS_ERR(fid))
+                        return fid;
 
-        if (ds == dentry)
+                v9fs_fid_add(dentry->d_sb->s_root, fid);
+        }
+        /* If we are root ourself just return that */
+        if (dentry->d_sb->s_root == dentry)
                 return fid;
-
-        wnames = kmalloc(sizeof(char *) * n, GFP_KERNEL);
-        if (!wnames)
-                return ERR_PTR(-ENOMEM);
-
-        for (d = dentry, i = (n-1); i >= 0; i--, d = d->d_parent)
-                wnames[i] = (char *) d->d_name.name;
-
+        /*
+         * Do a multipath walk with attached root.
+         * When walking parent we need to make sure we
+         * don't have a parallel rename happening
+         */
+        down_read(&v9ses->rename_sem);
+        n  = build_path_from_dentry(v9ses, dentry, &wnames);
+        if (n < 0) {
+                fid = ERR_PTR(n);
+                goto err_out;
+        }
         clone = 1;
         i = 0;
         while (i < n) {
                 l = min(n - i, P9_MAXWELEM);
+                /*
+                 * We need to hold rename lock when doing a multipath
+                 * walk to ensure none of the patch component change
+                 */
                 fid = p9_client_walk(fid, l, &wnames[i], clone);
                 if (IS_ERR(fid)) {
                         if (old_fid) {
@@ -194,15 +234,17 @@ struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
                                 p9_client_clunk(old_fid);
                         }
                         kfree(wnames);
-                        return fid;
+                        goto err_out;
                 }
                 old_fid = fid;
                 i += l;
                 clone = 0;
         }
-
         kfree(wnames);
+fid_out:
         v9fs_fid_add(dentry, fid);
+err_out:
+        up_read(&v9ses->rename_sem);
         return fid;
 }
 
diff --git a/fs/9p/v9fs.c b/fs/9p/v9fs.c
index 3c492011221c..38dc0e067599 100644
--- a/fs/9p/v9fs.c
+++ b/fs/9p/v9fs.c
@@ -237,6 +237,7 @@ struct p9_fid *v9fs_session_init(struct v9fs_session_info *v9ses,
                 __putname(v9ses->uname);
                 return ERR_PTR(-ENOMEM);
         }
+        init_rwsem(&v9ses->rename_sem);
 
         rc = bdi_setup_and_register(&v9ses->bdi, "9p", BDI_CAP_MAP_COPY);
         if (rc) {
diff --git a/fs/9p/v9fs.h b/fs/9p/v9fs.h
index bec4d0bcb458..4c963c9fc41f 100644
--- a/fs/9p/v9fs.h
+++ b/fs/9p/v9fs.h
@@ -104,6 +104,7 @@ struct v9fs_session_info {
         struct p9_client *clnt; /* 9p client */
         struct list_head slist; /* list of sessions registered with v9fs */
         struct backing_dev_info bdi;
+        struct rw_semaphore rename_sem;
 };
 
 struct p9_fid *v9fs_session_init(struct v9fs_session_info *, const char *,
diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
index 39352ef954dc..75c261fdc7b4 100644
--- a/fs/9p/vfs_inode.c
+++ b/fs/9p/vfs_inode.c
@@ -948,6 +948,7 @@ static struct dentry *v9fs_vfs_lookup(struct inode *dir, struct dentry *dentry,
 
         sb = dir->i_sb;
         v9ses = v9fs_inode2v9ses(dir);
+        /* We can walk d_parent because we hold the dir->i_mutex */
         dfid = v9fs_fid_lookup(dentry->d_parent);
         if (IS_ERR(dfid))
                 return ERR_CAST(dfid);
@@ -1055,27 +1056,33 @@ v9fs_vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
                 goto clunk_olddir;
         }
 
+        down_write(&v9ses->rename_sem);
         if (v9fs_proto_dotl(v9ses)) {
                 retval = p9_client_rename(oldfid, newdirfid,
                                         (char *) new_dentry->d_name.name);
                 if (retval != -ENOSYS)
                         goto clunk_newdir;
         }
+        if (old_dentry->d_parent != new_dentry->d_parent) {
+                /*
+                 * 9P .u can only handle file rename in the same directory
+                 */
 
-        /* 9P can only handle file rename in the same directory */
-        if (memcmp(&olddirfid->qid, &newdirfid->qid, sizeof(newdirfid->qid))) {
                 P9_DPRINTK(P9_DEBUG_ERROR,
                                 "old dir and new dir are different\n");
                 retval = -EXDEV;
                 goto clunk_newdir;
         }
-
         v9fs_blank_wstat(&wstat);
         wstat.muid = v9ses->uname;
         wstat.name = (char *) new_dentry->d_name.name;
         retval = p9_client_wstat(oldfid, &wstat);
 
 clunk_newdir:
+        if (!retval)
+                /* successful rename */
+                d_move(old_dentry, new_dentry);
+        up_write(&v9ses->rename_sem);
         p9_client_clunk(newdirfid);
 
 clunk_olddir:
diff --git a/fs/9p/vfs_super.c b/fs/9p/vfs_super.c
index 0a2e2030c844..4b9ede0b41b7 100644
--- a/fs/9p/vfs_super.c
+++ b/fs/9p/vfs_super.c
@@ -287,4 +287,5 @@ struct file_system_type v9fs_fs_type = {
         .get_sb = v9fs_get_sb,
         .kill_sb = v9fs_kill_super,
         .owner = THIS_MODULE,
+        .fs_flags = FS_RENAME_DOES_D_MOVE,
 };