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Message-ID: <20250908125526.GY616306@nvidia.com>
Date: Mon, 8 Sep 2025 09:55:26 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>,
	Matthew Wilcox <willy@...radead.org>, Guo Ren <guoren@...nel.org>,
	Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>,
	"David S . Miller" <davem@...emloft.net>,
	Andreas Larsson <andreas@...sler.com>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Vishal Verma <vishal.l.verma@...el.com>,
	Dave Jiang <dave.jiang@...el.com>, Nicolas Pitre <nico@...xnic.net>,
	Muchun Song <muchun.song@...ux.dev>,
	Oscar Salvador <osalvador@...e.de>,
	David Hildenbrand <david@...hat.com>,
	Konstantin Komarov <almaz.alexandrovich@...agon-software.com>,
	Baoquan He <bhe@...hat.com>, Vivek Goyal <vgoyal@...hat.com>,
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	Reinette Chatre <reinette.chatre@...el.com>,
	Dave Martin <Dave.Martin@....com>,
	James Morse <james.morse@....com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
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	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>, Hugh Dickins <hughd@...gle.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Uladzislau Rezki <urezki@...il.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Andrey Konovalov <andreyknvl@...il.com>,
	Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-csky@...r.kernel.org,
	linux-mips@...r.kernel.org, linux-s390@...r.kernel.org,
	sparclinux@...r.kernel.org, nvdimm@...ts.linux.dev,
	linux-cxl@...r.kernel.org, linux-mm@...ck.org,
	ntfs3@...ts.linux.dev, kexec@...ts.infradead.org,
	kasan-dev@...glegroups.com
Subject: Re: [PATCH 06/16] mm: introduce the f_op->mmap_complete, mmap_abort
 hooks

On Mon, Sep 08, 2025 at 12:10:37PM +0100, Lorenzo Stoakes wrote:
> We have introduced the f_op->mmap_prepare hook to allow for setting up a
> VMA far earlier in the process of mapping memory, reducing problematic
> error handling paths, but this does not provide what all
> drivers/filesystems need.
> 
> In order to supply this, and to be able to move forward with removing
> f_op->mmap altogether, introduce f_op->mmap_complete.
> 
> This hook is called once the VMA is fully mapped and everything is done,
> however with the mmap write lock and VMA write locks held.
> 
> The hook is then provided with a fully initialised VMA which it can do what
> it needs with, though the mmap and VMA write locks must remain held
> throughout.
> 
> It is not intended that the VMA be modified at this point, attempts to do
> so will end in tears.

The commit message should call out if this has fixed the race
condition with unmap mapping range and prepopulation in mmap()..

> @@ -793,6 +793,11 @@ struct vm_area_desc {
>  	/* Write-only fields. */
>  	const struct vm_operations_struct *vm_ops;
>  	void *private_data;
> +	/*
> +	 * A user-defined field, value will be passed to mmap_complete,
> +	 * mmap_abort.
> +	 */
> +	void *mmap_context;

Seem strange, private_data and mmap_context? Something actually needs
both?

Jason

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