Re: 6.19 tmpfs __d_lookup() lockup

[Al Viro <viro@zeniv.linux.org.uk>]

On Thu, Dec 11, 2025 at 09:57:15PM -0800, Hugh Dickins wrote:

> No, sad to say, CONFIG_UNICODE is not set.
> 
> (I see why you're asking, I did notice from the diff that the
> case-folding stuff in shmem.c used to do something different but
> now the same in several places; but the case-folding people will
> have to look out for themselves, it's beyond me.)
> 
> (And yes, I was being stupid in my previous response: once I looked
> at how simple d_in_lookup() is, I understood your "hitting"; but at
> least I gave the right answer, no, that warning does not show up.)

A few more things to check:

1) do we, by any chance, ever see dentry_free() called with
dentry->d_flags & DCACHE_PERSISTENT?

2) does d_make_persistent() ever call __d_rehash() when called with
dentry->d_sb->s_magic == TMPFS_MAGIC?

3) is shmem_whiteout() ever called?  If that's the case, could you try
to remove that d_rehash() call in it and see what happens?  Because
that's another place where shmem is playing odd games...