Re: [PATCH 3/3] ovl: provide private lockdep class for dentry->dep_map

[Amir Goldstein]

On Sat, Oct 3, 2026 at 12:42 AM NeilBrown <neilb@xxxxxxxxxxx> wrote:
>
> From: NeilBrown <neil@xxxxxxxxxx>
>
> Now that d_alloc_parallel() locking is tracked by lockdep, ovl needs to
> take care that it doesn't trigger on deliberate recursion into
> subordinate filesystems.  As ovl can stack over itself, the use
> of the per-file_system_type d_lookup_key is not enough.
>
> So provide a .d_init() function to update the map as it already done for
> i_rwsem and ovl_inode.lock.
>
> Reported-and-tested-by: "Borah, Chaitanya Kumar" <chaitanya.kumar.borah@xxxxxxxxx>
> Link: https://lore.kernel.org/all/e3772a51-eabc-4c31-b73d-f3187bf1b3b2@xxxxxxxxx/
> Fixes: 59492f9991dc ("VFS: add lockdep monitoring of DCACHE_PAR_LOOKUP lock.")
> Signed-off-by: NeilBrown <neil@xxxxxxxxxx>

Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx>

> ---
>  fs/overlayfs/inode.c     |  1 -
>  fs/overlayfs/overlayfs.h |  2 ++
>  fs/overlayfs/super.c     | 19 +++++++++++++++++++
>  3 files changed, 21 insertions(+), 1 deletion(-)
>
> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
> index 401cb8c75520..bf40198c8b8a 100644
> --- a/fs/overlayfs/inode.c
> +++ b/fs/overlayfs/inode.c
> @@ -816,7 +816,6 @@ static const struct address_space_operations ovl_aops = {
>   * - OVL_I(inode)->lock                        (ovl_inode_lock[1])
>   * - upper_mnt->mnt_sb->s_writers      (ovl_want_write[0])
>   */
> -#define OVL_MAX_NESTING FILESYSTEM_MAX_STACK_DEPTH
>
>  static inline void ovl_lockdep_annotate_inode_mutex_key(struct inode *inode)
>  {
> diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
> index e0d8c6152e9f..64cbe4c4bd3e 100644
> --- a/fs/overlayfs/overlayfs.h
> +++ b/fs/overlayfs/overlayfs.h
> @@ -16,6 +16,8 @@
>  #undef pr_fmt
>  #define pr_fmt(fmt) "overlayfs: " fmt
>
> +#define OVL_MAX_NESTING FILESYSTEM_MAX_STACK_DEPTH
> +
>  enum ovl_path_type {
>         __OVL_PATH_UPPER        = (1 << 0),
>         __OVL_PATH_MERGE        = (1 << 1),
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index e487597337e8..08147799e47c 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -163,10 +163,28 @@ static int ovl_dentry_weak_revalidate(struct dentry *dentry, unsigned int flags)
>         return ovl_dentry_revalidate_common(dentry, flags, true);
>  }
>
> +#ifdef CONFIG_LOCKDEP
> +static int ovl_dentry_init(struct dentry *dentry)
> +{
> +       static struct lock_class_key ovl_d_lock_key[OVL_MAX_NESTING];
> +       int depth = dentry->d_sb->s_stack_depth - 1;
> +
> +       if (WARN_ON_ONCE(depth < 0 || depth >= OVL_MAX_NESTING))
> +               depth = 0;
> +
> +       lockdep_set_class(dentry, &ovl_d_lock_key[depth]);
> +
> +       return 0;
> +}
> +#else
> +#define ovl_dentry_init NULL
> +#endif
> +
>  static const struct dentry_operations ovl_dentry_operations = {
>         .d_real = ovl_d_real,
>         .d_revalidate = ovl_dentry_revalidate,
>         .d_weak_revalidate = ovl_dentry_weak_revalidate,
> +       .d_init = ovl_dentry_init,
>  };
>
>  #if IS_ENABLED(CONFIG_UNICODE)
> @@ -176,6 +194,7 @@ static const struct dentry_operations ovl_dentry_ci_operations = {
>         .d_weak_revalidate = ovl_dentry_weak_revalidate,
>         .d_hash = generic_ci_d_hash,
>         .d_compare = generic_ci_d_compare,
> +       .d_init = ovl_dentry_init,
>  };
>  #endif
>
> --
> 2.50.0.107.gf914562f5916.dirty
>