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Howlett" , Vlastimil Babka , David Hildenbrand , Mike Rapoport , Maxime Ripard , Thomas Zimmermann , David Airlie , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Arnd Bergmann , Muchun Song , Oscar Salvador , "Matthew Wilcox (Oracle)" , Jan Kara , Marc Zyngier , Oliver Upton , Catalin Marinas , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , "David S. Miller" , Andreas Larsson , Alexander Viro , Christian Brauner , Matthew Brost , Chengming Zhou , Michal Hocko , Miklos Szeredi , Xu Xin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v3 01/40] mm/vma: fix mmap_prepare file handling, remove file_doesnt_need_get Message-ID: References: <20260917-b4-mmap-prepare-vma-flag-sanify-v3-0-4583d8a23bca@kernel.org> <20260917-b4-mmap-prepare-vma-flag-sanify-v3-1-4583d8a23bca@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam06 X-Stat-Signature: bij8kfnna98r4zot5wjjwdaskshawhhm X-Rspam-User: X-Rspamd-Queue-Id: 81EB6140008 X-HE-Tag: 1790328658-980568 X-HE-Meta: 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 JZ/ZkX6E 4AC6IX4flnnmAthOv1pJkBsrO3Er7KxdZNreP8TRQsWqYxfpD7CJHCp21rJCzvDuMzp6+DqR3+55HA7Icp7AEN5OoSnHuVAc8AVDE5pgRlpsuhHeDbW1jj8rdvadcnOzLwvj28GNChljh9zvMspkf0Qi5EczmipQoPzlUYhLuRh7P8Ccc4QxeHlLxDl2eqyfGJlDzJMrRynOUsC7jwvp06OVrSnlQqa7SobhqWE6MkIiDOiDzMBlKqhAZSgJqhybel8It4d6VsaXRrx4+I0BvC9gBSnJ+ap5T2PB6y8qstfmvE2g= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Sep 24, 2026 at 12:28:39PM -0400, Gregory Price wrote: > On Thu, Sep 17, 2026 at 05:22:10PM +0100, Lorenzo Stoakes (ARM) wrote: > > +static void put_map(struct mmap_state *map) > > +{ > ... > > + if (map->vm_file && !map_same_file(map)) > > + fput(map->vm_file); > ... > > diff --git a/mm/vma.h b/mm/vma.h > > index e97bd2dfa786..f15faa83f3d6 100644 > > --- a/mm/vma.h > > +++ b/mm/vma.h > > @@ -394,8 +394,10 @@ static inline void compat_set_vma_from_desc(struct vm_area_struct *vma, > > > > + if (desc->vm_file != vma->vm_file) { > > + fput(vma->vm_file); > > > Sashiko pointed out that this could be null if the vma is "anonymized". Sashiko is wrong :) I wish I could mark responses like that so it didn't regenerate them on each respin. (I always run sashiko output received for each series through a frontier LLM anyway + fix stuff that is real, see the changelog for series for those things that were valid) You can't reach this code without a vma->vm_file. > > Previously we'd discussed that anonymizing a file folio is more of a > wart than a feature, and IIRC you intended to remove that (i think?) > when you removed zero-file mapping "anonymization" so some of this VMA > stuff could be detangled. The anonymising as existed before clears vma->vm_ops not vma->vm_file. The new _actual_ anonymisation for MAP_PRIVATE-/dev/zero clears vma->vm_file but only on the raw mmap_prepare non-compat path, stacked MAP_PRIVATE-/dev/zero is not supported as a means of getting anonymous memory (and would be a really strange thing to do anyway). (In general stacked file systems only operate on regular files anyway). > > If this is an intermediate state, do we still need to manage this NULL > scenario, and when we drop the anonymization mechanism we add a WARN() > that says someone is being naughty? Nope not at all. No code path can get here with NULL vm_file and it's already the case that a driver setting the wrong thing NULL could trigger a NULL pointer deref anyway. Nothing in-tree does anything like this and out of tree drivers can trigger stuff if they want but it's not for us to worry about (they already can do that locally :P) :) > > ~Gregory -- Cheers, Lorenzo