Re: [PATCH 6.1.y 1/1] fs: relax assertions on failure to encode file handles

["Manthey, Norbert" <nmanthey@amazon.de>]

On Mon, 2025-09-01 at 22:00 +0200, Greg Kroah-Hartman wrote:
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> On Mon, Sep 01, 2025 at 09:54:03PM +0200, Greg Kroah-Hartman wrote:
> > On Mon, Sep 01, 2025 at 03:35:59PM +0000, Norbert Manthey wrote:
> > > From: Amir Goldstein <amir73il@gmail.com>
> > > 
> > > commit 974e3fe0ac61de85015bbe5a4990cf4127b304b2 upstream.
> > > 
> > > Encoding file handles is usually performed by a filesystem >encode_fh()
> > > method that may fail for various reasons.
> > > 
> > > The legacy users of exportfs_encode_fh(), namely, nfsd and
> > > name_to_handle_at(2) syscall are ready to cope with the possibility
> > > of failure to encode a file handle.
> > > 
> > > There are a few other users of exportfs_encode_{fh,fid}() that
> > > currently have a WARN_ON() assertion when ->encode_fh() fails.
> > > Relax those assertions because they are wrong.
> > > 
> > > The second linked bug report states commit 16aac5ad1fa9 ("ovl: support
> > > encoding non-decodable file handles") in v6.6 as the regressing commit,
> > > but this is not accurate.
> > > 
> > > The aforementioned commit only increases the chances of the assertion
> > > and allows triggering the assertion with the reproducer using overlayfs,
> > > inotify and drop_caches.
> > > 
> > > Triggering this assertion was always possible with other filesystems and
> > > other reasons of ->encode_fh() failures and more particularly, it was
> > > also possible with the exact same reproducer using overlayfs that is
> > > mounted with options index=on,nfs_export=on also on kernels < v6.6.
> > > Therefore, I am not listing the aforementioned commit as a Fixes commit.
> > > 
> > > Backport hint: this patch will have a trivial conflict applying to
> > > v6.6.y, and other trivial conflicts applying to stable kernels < v6.6.
> > > 
> > > Reported-by: syzbot+ec07f6f5ce62b858579f@syzkaller.appspotmail.com
> > > Tested-by: syzbot+ec07f6f5ce62b858579f@syzkaller.appspotmail.com
> > > Closes: https://lore.kernel.org/linux-unionfs/671fd40c.050a0220.4735a.024f.GAE@google.com/
> > > Reported-by: Dmitry Safonov <dima@arista.com>
> > > Closes: https://lore.kernel.org/linux-
> > > fsdevel/CAGrbwDTLt6drB9eaUagnQVgdPBmhLfqqxAf3F+Juqy_o6oP8uw@mail.gmail.com/
> > > Cc: stable@vger.kernel.org
> > > Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> > > Link: https://lore.kernel.org/r/20241219115301.465396-1-amir73il@gmail.com
> > > Signed-off-by: Christian Brauner <brauner@kernel.org>
> > > Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> > > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > 
> > I never signed off on the original commit, so why was this added?

This cherry-pick is not for the upstream commit, but for the backport on the 6.6 tree. The
respective commit hash is given in the backport line. Is this additional information you would like
to have in the commit message?

> > 
> > > 
> > > (fuzzy picked from commit f47c834a9131ae64bee3c462f4e610c67b0a000f)
> > > Applied with LLM-adjusted hunks for 1 functions from us.amazon.nova
> > > - Changed the function call from `exportfs_encode_fid` to `exportfs_encode_inode_fh` to match
> > > the destination code.
> 
> Wait, that was just fuzz matching, the real body didn't even change.
> 
> > > - Removed the warning message as per the patch.
> 
> I do not understand this change, what exactly was this?

I need to rewrite (here: drop) this manually. The LLM was also describing the content of the
original patch, not only the diff it created. 

> 
> > Please put this in the proper place, and in the proper format, if you
> > want to add "notes" to the backport.

IIUC, the changes applied to the patch so that it applies should come above my SOB, no? What's the
format requirement (except the 80-100 char limit)?

I am aware of the discussions about AI generated code. I wanted to explicitly mention the AI use, if
it was used as backporting helper. Do you suggest to still move this into the notes section of the
commit and sent patch, instead of having this in the commit itself?

> > 
> > But really, it took a LLM to determine an abi change?  That feels like
> > total overkill as you then had to actually manually check it as well.
> > But hey, it's your cpu cycles to burn, not mine...

I prefer reviewing the code instead of writing/massaging all of it, and on success have the change
tested/validated automatically before I reviewing.

> 
> 
> Again, total overkill, 1 minute doing a simple git merge resolution
> would have done the same thing, right?

For this example, yes, I agree. There are more complex commits where this works as well.

> 
> confused as to why this took a whole new tool?  We have good merge
> resolution tools for git these days, what's wrong with using one of the
> many ones out there?

There is nothing wrong using any other tool. The git-llm-pick tool allows to automatically backport
more commits and supports user specified validation for the changes. The LLM is only the last
attempt. A human needs to review the output either way, and eventually do the
backport interactively.

Best,
Norbert

> 
> thanks,
> 
> greg k-h





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