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

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Message-ID: <pt5ni6ofhzbiiemnmrueg3w2hicfmi5qvqctz4ixasl2qrgjo7@dr5qcp52txuf>
Date: Wed, 14 May 2025 09:50:55 +0100
From: Pedro Falcato <pfalcato@...e.de>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, 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>, 
	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 Wed, May 14, 2025 at 10:42:53AM +0200, Vlastimil Babka wrote:
> 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>

Reviewed-by: Pedro Falcato <pfalcato@...e.de>

-- 
Pedro