Re: [syzbot ci] Re: Create and use APIs to centralise locking for directory ops.

NeilBrown
2025-11-12T22:50:48Z

On Thu, 06 Nov 2025, syzbot ci wrote:
> syzbot ci has tested the following series
>
> [v5] Create and use APIs to centralise locking for directory ops.
> https://lore.kernel.org/all/20251106005333.956321-1-neilb@ownmail.net
> * [PATCH v5 01/14] debugfs: rename end_creating() to debugfs_end_creating()
> * [PATCH v5 02/14] VFS: introduce start_dirop() and end_dirop()
> * [PATCH v5 03/14] VFS: tidy up do_unlinkat()
> * [PATCH v5 04/14] VFS/nfsd/cachefiles/ovl: add start_creating() and end_creating()
> * [PATCH v5 05/14] VFS/nfsd/cachefiles/ovl: introduce start_removing() and end_removing()
> * [PATCH v5 06/14] VFS: introduce start_creating_noperm() and start_removing_noperm()
> * [PATCH v5 07/14] VFS: introduce start_removing_dentry()
> * [PATCH v5 08/14] VFS: add start_creating_killable() and start_removing_killable()
> * [PATCH v5 09/14] VFS/nfsd/ovl: introduce start_renaming() and end_renaming()
> * [PATCH v5 10/14] VFS/ovl/smb: introduce start_renaming_dentry()
> * [PATCH v5 11/14] Add start_renaming_two_dentries()
> * [PATCH v5 12/14] ecryptfs: use new start_creating/start_removing APIs
> * [PATCH v5 13/14] VFS: change vfs_mkdir() to unlock on failure.
> * [PATCH v5 14/14] VFS: introduce end_creating_keep()
>
> and found the following issues:
> * WARNING: lock held when returning to user space in start_creating
> * possible deadlock in mnt_want_write
>
> Full report is available here:
> https://ci.syzbot.org/series/4f406e4d-6aba-457a-b9c1-21f4407176a0
>
> ***
>
> WARNING: lock held when returning to user space in start_creating

I think this was due to a bug in
VFS: change vfs_mkdir() to unlock on failure.
in ovl_create_real()

That patch removed a end_creating() call that was after
ovl_create_real() returned failure, but didn't add end_creating() in
ovl_create_real() on failure. So it could exit with the lock still
held.

This patch should fix it, particularly the second hunk.

Thanks,
NeilBrown

diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index a4a0dc261310..739f974dc258 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -187,7 +187,7 @@ struct dentry *ovl_create_real(struct ovl_fs *ofs, struct dentry *parent,
if (!err && ofs->casefold != ovl_dentry_casefolded(newdentry)) {
pr_warn_ratelimited("wrong inherited casefold (%pd2)\n",
newdentry);
- dput(newdentry);
+ end_creating(newdentry);
err = -EINVAL;
}
break;
@@ -237,8 +237,7 @@ struct dentry *ovl_create_real(struct ovl_fs *ofs, struct dentry *parent,
}
out:
if (err) {
- if (!IS_ERR(newdentry))
- dput(newdentry);
+ end_creating(newdentry);
return ERR_PTR(err);
}
return newdentry;