ovl: defer upper dir lock to tempfile link

On copy up of regular file using an O_TMPFILE, lock upper dir only
before linking the tempfile in place.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

2 files changed, 38 insertions, 30 deletions

diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index 5e8fd99557e1..28711af7f9db 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -316,6 +316,35 @@ static int ovl_set_origin(struct dentry *dentry, struct dentry *lower,
         return err;
 }
 
+static int ovl_install_temp(struct dentry *workdir, struct dentry *upperdir,
+                            struct dentry *dentry,
+                            struct dentry *temp, struct kstat *pstat,
+                            bool tmpfile, struct dentry **newdentry)
+{
+        int err;
+        struct dentry *upper;
+        struct inode *udir = d_inode(upperdir);
+
+        upper = lookup_one_len(dentry->d_name.name, upperdir,
+                               dentry->d_name.len);
+        if (IS_ERR(upper))
+                return PTR_ERR(upper);
+
+        if (tmpfile)
+                err = ovl_do_link(temp, udir, upper, true);
+        else
+                err = ovl_do_rename(d_inode(workdir), temp, udir, upper, 0);
+
+        /* Restore timestamps on parent (best effort) */
+        if (!err) {
+                ovl_set_timestamps(upperdir, pstat);
+                *newdentry = dget(tmpfile ? upper : temp);
+        }
+        dput(upper);
+
+        return err;
+}
+
 static int ovl_copy_up_locked(struct dentry *workdir, struct dentry *upperdir,
                               struct dentry *dentry, struct path *lowerpath,
                               struct kstat *stat, const char *link,
@@ -324,7 +353,6 @@ static int ovl_copy_up_locked(struct dentry *workdir, struct dentry *upperdir,
         struct inode *wdir = workdir->d_inode;
         struct inode *udir = upperdir->d_inode;
         struct dentry *newdentry = NULL;
-        struct dentry *upper = NULL;
         struct dentry *temp = NULL;
         int err;
         const struct cred *old_creds = NULL;
@@ -371,16 +399,7 @@ static int ovl_copy_up_locked(struct dentry *workdir, struct dentry *upperdir,
                 BUG_ON(upperpath.dentry != NULL);
                 upperpath.dentry = temp;
 
-                if (tmpfile) {
-                        inode_unlock(udir);
-                        err = ovl_copy_up_data(lowerpath, &upperpath,
-                                               stat->size);
-                        inode_lock_nested(udir, I_MUTEX_PARENT);
-                } else {
-                        err = ovl_copy_up_data(lowerpath, &upperpath,
-                                               stat->size);
-                }
-
+                err = ovl_copy_up_data(lowerpath, &upperpath, stat->size);
                 if (err)
                         goto out_cleanup;
         }
@@ -408,29 +427,21 @@ static int ovl_copy_up_locked(struct dentry *workdir, struct dentry *upperdir,
                         goto out_cleanup;
         }
 
-        upper = lookup_one_len(dentry->d_name.name, upperdir,
-                               dentry->d_name.len);
-        if (IS_ERR(upper)) {
-                err = PTR_ERR(upper);
-                upper = NULL;
-                goto out_cleanup;
+        if (tmpfile) {
+                inode_lock_nested(udir, I_MUTEX_PARENT);
+                err = ovl_install_temp(workdir, upperdir, dentry, temp, pstat,
+                                       tmpfile, &newdentry);
+                inode_unlock(udir);
+        } else {
+                err = ovl_install_temp(workdir, upperdir, dentry, temp, pstat,
+                                       tmpfile, &newdentry);
         }
-
-        if (tmpfile)
-                err = ovl_do_link(temp, udir, upper, true);
-        else
-                err = ovl_do_rename(wdir, temp, udir, upper, 0);
         if (err)
                 goto out_cleanup;
 
-        newdentry = dget(tmpfile ? upper : temp);
         ovl_inode_update(d_inode(dentry), newdentry);
-
-        /* Restore timestamps on parent (best effort) */
-        ovl_set_timestamps(upperdir, pstat);
 out:
         dput(temp);
-        dput(upper);
         return err;
 
 out_cleanup:
@@ -496,10 +507,8 @@ static int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
                         goto out_done;
                 }
 
-                inode_lock_nested(upperdir->d_inode, I_MUTEX_PARENT);
                 err = ovl_copy_up_locked(workdir, upperdir, dentry, lowerpath,
                                          stat, link, &pstat, true);
-                inode_unlock(upperdir->d_inode);
                 ovl_copy_up_end(dentry);
                 goto out_done;
         }
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 22ed51f80e58..c80b4bf1e64f 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -236,7 +236,6 @@ void ovl_inode_update(struct inode *inode, struct dentry *upperdentry)
 {
         struct inode *upperinode = d_inode(upperdentry);
 
-        WARN_ON(!inode_is_locked(upperdentry->d_parent->d_inode));
         WARN_ON(OVL_I(inode)->__upperdentry);
 
         /*