linux-kernel - Re: [PATCH] mm: remove WARN_ON_ONCE() in file_has_valid_mmap

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Message-ID: <e0e5abd4-3303-458b-8f55-1e3157d25cd1@lucifer.local>
Date: Wed, 14 May 2025 11:23:24 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: David Hildenbrand <david@...hat.com>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
        Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH] mm: remove WARN_ON_ONCE() in file_has_valid_mmap_hooks()

Andrew:

(to save you having to dive into rest of thread)

Could you add the Fixes line suggested by David below?

Thanks! :)

On Wed, May 14, 2025 at 10:49:57AM +0200, David Hildenbrand wrote:
> On 14.05.25 10:40, Lorenzo Stoakes wrote:
> > Having encountered a trinity report in linux-next (Linked in the 'Closes'
> > tag) it appears that there are legitimate situations where a file-backed
> > mapping can be acquired but no file->f_op->mmap or file->f_op->mmap_prepare
> > is set, at which point do_mmap() should simply error out with -ENODEV.
> >
> > Since previously we did not warn in this scenario and it appears we rely
> > upon this, restore this situation, while retaining a WARN_ON_ONCE() for the
> > case where both are set, which is absolutely incorrect and must be
> > addressed and thus always requires a warning.
> >
> > If further work is required to chase down precisely what is causing this,
> > then we can later restore this, but it makes no sense to hold up this
> > series to do so, as this is existing and apparently expected behaviour.
> >
> > Reported-by: kernel test robot <oliver.sang@...el.com>
> > Closes: https://lore.kernel.org/oe-lkp/202505141434.96ce5e5d-lkp@intel.com
> > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> > ---
> >
> > Andrew -
> >
> > Since this series is in mm-stable we should take this fix there asap (and
> > certainly get it to -next to fix any further error reports). I didn't know
> > whether it was best for it to be a fix-patch or not, so have sent
> > separately so you can best determine what to do with it :)
>
> A couple more days in mm-unstable probably wouldn't have hurt here,
> especially given that I recall reviewing + seeing review yesterday?
>
> Fixes: c84bf6dd2b83 ("mm: introduce new .mmap_prepare() file callback")
>
> Acked-by: David Hildenbrand <david@...hat.com>
>
> --
> Cheers,
>
> David / dhildenb
>