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: <7821b672-eae7-4730-afe4-b72b80ac6ea2@suse.cz>
Date: Fri, 1 Aug 2025 12:54:59 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org
Cc: 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, shuah@...nel.org, adobriyan@...il.com,
 brauner@...nel.org, josef@...icpanda.com, yebin10@...wei.com,
 linux@...ssschuh.net, 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 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?

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().