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

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Message-ID: <9b5d232e-7579-42a9-bcbe-a4674bf76fe4@suse.cz>
Date: Wed, 14 May 2025 10:42:53 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: David Hildenbrand <david@...hat.com>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>, 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 5/14/25 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>

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

> ---
> 
> 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 :)
> 
> Thanks, Lorenzo
> 
>  include/linux/fs.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index e2721a1ff13d..09c8495dacdb 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2248,7 +2248,7 @@ static inline bool file_has_valid_mmap_hooks(struct file *file)
>  	/* Hooks are mutually exclusive. */
>  	if (WARN_ON_ONCE(has_mmap && has_mmap_prepare))
>  		return false;
> -	if (WARN_ON_ONCE(!has_mmap && !has_mmap_prepare))
> +	if (!has_mmap && !has_mmap_prepare)
>  		return false;
> 
>  	return true;
> --
> 2.49.0