linux-kernel - Re: [PATCH v3 1/2] mm: protect free_pgtables with mmap_lock write lock in exit

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Date:   Tue, 7 Dec 2021 22:07:16 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     akpm@...ux-foundation.org, mhocko@...nel.org, mhocko@...e.com,
        rientjes@...gle.com, hannes@...xchg.org, guro@...com,
        riel@...riel.com, minchan@...nel.org, kirill@...temov.name,
        aarcange@...hat.com, christian@...uner.io, hch@...radead.org,
        oleg@...hat.com, david@...hat.com, jannh@...gle.com,
        shakeelb@...gle.com, luto@...nel.org, christian.brauner@...ntu.com,
        fweimer@...hat.com, jengelh@...i.de, timmurray@...gle.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@...roid.com
Subject: Re: [PATCH v3 1/2] mm: protect free_pgtables with mmap_lock write
 lock in exit_mmap

On Tue, Dec 07, 2021 at 01:50:30PM -0800, Suren Baghdasaryan wrote:
> - Added a comment for vm_operations_struct::close, documenting restriction for
> taking mmap_lock in the callback, per Michal Hocko and Matthew Wilcox

This should be a separate patch because it stands alone, but ...

>  struct vm_operations_struct {
>  	void (*open)(struct vm_area_struct * area);
> +    /*
> +     * Called with mmap_lock lock held for write from __split_vma and
> +     * remove_vma, therefore should never take that lock.
> +     */

Your whitespace indentation is weird.  And it'd be nice to make this a
kernel-doc comment (I know none of the others are, but that should be
fixed too).  And naming the functions that call it is wrong too.

	/**
	 * @close: Called when the VMA is being removed from the MM.
	 * Context: Caller holds mmap_lock.
	 */