linux-kernel - Re: [PATCH 2/3] fs/proc/task_mmu: factor out proc_maps_private fields used by PROCMAP

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Message-ID: <CAJuCfpEhC77ZD7Zvg+9nqb=DAj2kufnLGpD72gXFbQ5Bbp-ayQ@mail.gmail.com>
Date: Fri, 1 Aug 2025 08:33:24 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: akpm@...ux-foundation.org, Liam.Howlett@...cle.com, 
	lorenzo.stoakes@...cle.com, david@...hat.com, peterx@...hat.com, 
	jannh@...gle.com, hannes@...xchg.org, mhocko@...nel.org, paulmck@...nel.org, 
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	willy@...radead.org, osalvador@...e.de, andrii@...nel.org, 
	ryan.roberts@....com, christophe.leroy@...roup.eu, tjmercier@...gle.com, 
	kaleshsingh@...gle.com, aha310510@...il.com, linux-kernel@...r.kernel.org, 
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, 
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 2/3] fs/proc/task_mmu: factor out proc_maps_private fields
 used by PROCMAP_QUERY

On Fri, Aug 1, 2025 at 3:55 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>
> On 8/1/25 00:00, Suren Baghdasaryan wrote:
> > Refactor struct proc_maps_private so that the fields used by PROCMAP_QUERY
> > ioctl are moved into a separate structure. In the next patch this allows
> > ioctl to reuse some of the functions used for reading /proc/pid/maps
> > without using file->private_data. This prevents concurrent modification
> > of file->private_data members by ioctl and /proc/pid/maps readers.
> >
> > The change is pure code refactoring and has no functional changes.
>
> I think you'll need to adjust task_nommu.c as well, minimally I see it also
> has m_start() acceding priv->mm directly so it won't compile now?

Ugh, yes, you are right. I'll need to adjust NOMMU code as well. And
kernel test bot seems to be complaining already :)

>
> Also not sure about the naming, struct is named "proc_maps_query_data" and
> priv field named "query" but the read() implementation uses it too, via
> priv->query, although it does no PROCMAP_QUERY.
>
> Seems to me it's actually something like a mm+vma locking context? Which can
> be either stored in proc_maps_private for read() operations, or local
> on-stack for ioctl().

Yes, I struggled with the naming of this structure. Any help with this
is highly appreciated.