linux-kernel - Re: [PATCH 1/2] tomoyo: Convert get_user_pages*() to pin_user

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Date:   Sat, 7 Nov 2020 11:17:52 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Souptick Joarder <jrdr.linux@...il.com>, <takedakn@...data.co.jp>,
        <penguin-kernel@...ove.SAKURA.ne.jp>, <jmorris@...ei.org>,
        <serge@...lyn.com>
CC:     <linux-security-module@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Jan Kara <jack@...e.cz>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH 1/2] tomoyo: Convert get_user_pages*() to
 pin_user_pages*()

On 11/7/20 1:04 AM, John Hubbard wrote:
> On 11/7/20 12:24 AM, Souptick Joarder wrote:
>> In 2019, we introduced pin_user_pages*() and now we are converting
>> get_user_pages*() to the new API as appropriate. [1] & [2] could
>> be referred for more information. This is case 5 as per document [1].
> 
> It turns out that Case 5 can be implemented via a better pattern, as long
> as we're just dealing with a page at a time, briefly:
> 
> lock_page()
> write to page's data
> unlock_page()
> 
> ...which neatly synchronizes with writeback and other fs activities.

Ahem, I left out a key step: set_page_dirty()!

lock_page()
write to page's data
set_page_dirty()
unlock_page()


thanks,
-- 
John Hubbard
NVIDIA