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

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Message-ID: <357de3b3-6f70-49c4-87d4-f6e38e7bec11@redhat.com>
Date: Wed, 14 May 2025 10:49:57 +0200
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: "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()

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