Re: [PATCH] debugfs: don't warn about uninitialized debugfs for an error parent

[Yohei Kojima]

On Thu, Sep 03, 2026 at 04:51:35PM +0500, Mikhail Gavrilov wrote:
> Since commit c3a280ff728a
> ("debugfs: warn if file creation failed due to uninitialized debugfs")
> every boot with CONFIG_REF_TRACKER=y and CONFIG_DEBUG_FS=y prints two
> errors before the root filesystem is mounted:
> 
>   debugfs: Unable to create file 'net_refcnt@(____ptrval____)',
>     debugfs is not initialized yet
>   debugfs: Unable to create file 'net_notrefcnt@(____ptrval____)',
>     debugfs is not initialized yet

Ugh... I should've noticed this...

> Move the IS_ERR(parent) check above the debugfs_initialized() test.  A
> caller passing an error parent is propagating an earlier failure, which is
> the pattern debugfs documents and which the warning is not aimed at.  A
> caller passing a valid or NULL parent too early - the case the warning was
> added for - still gets it.
> 
> One behaviour change: an early caller with an error parent now gets
> PTR_ERR(parent) back instead of -ENOENT.  All callers of these interfaces
> are documented to ignore the return value.

The new behavior looks better than the old one as it used to ignore
parent's errno and just returned ERR_PTR(-ENOENT).

> 
> Fixes: c3a280ff728a ("debugfs: warn if file creation failed due to uninitialized debugfs")
> Link: https://lore.kernel.org/all/6d1dc775f7d5e754d734907514534054f682bac5.1781171918.git.yk@xxxxxxxxx/
> Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@xxxxxxxxx>

I tested this patch on x86_64 (Intel Core i7-14700K), Gentoo, v7.3-rc1
(940de590b839), CONFIG_REF_TRACKER=y, CONFIG_DEBUG_FS=y, with KASAN and
lockdep enabled.

  $ diff -u before_patch after_patch 
  --- before_patch        2026-09-03 23:46:02.856774818 +0900
  +++ after_patch 2026-09-03 23:46:09.990259686 +0900
  @@ -1,8 +1,6 @@
   Yama: becoming mindful.
   SELinux:  Initializing.
  -debugfs: Unable to create file 'net_refcnt@(____ptrval____)', debugfs is not initialized yet
   stackdepot: allocating hash table of 131072 entries via kvcalloc
   stackdepot: allocating space for 8192 stack pools via kvcalloc
  -debugfs: Unable to create file 'net_notrefcnt@(____ptrval____)', debugfs is not initialized yet
   Mount-cache hash table entries: 65536 (order: 7, 524288 bytes, linear)
   Mountpoint-cache hash table entries: 65536 (order: 7, 524288 bytes, linear)

Tested-by: Yohei Kojima <yk@xxxxxxxxx>

Thank you for reporting and fixing this during rc!

Yohei