linux-kernel - Re: [PATCH -mm -V8] mm, swap: fix race between swapoff and some swap operations

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Date:   Wed, 27 Feb 2019 09:13:14 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Daniel Jordan <daniel.m.jordan@...cle.com>
Cc:     Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        Hugh Dickins <hughd@...gle.com>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Minchan Kim <minchan@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        "Tim Chen" <tim.c.chen@...ux.intel.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Jérôme Glisse <jglisse@...hat.com>,
        Michal Hocko <mhocko@...e.com>,
        David Rientjes <rientjes@...gle.com>,
        Rik van Riel <riel@...hat.com>, Jan Kara <jack@...e.cz>,
        Dave Jiang <dave.jiang@...el.com>,
        Aaron Lu <aaron.lu@...el.com>,
        Andrea Parri <andrea.parri@...rulasolutions.com>
Subject: Re: [PATCH -mm -V8] mm, swap: fix race between swapoff and some swap operations

Daniel Jordan <daniel.m.jordan@...cle.com> writes:

> On Tue, Feb 26, 2019 at 02:49:05PM +0800, Huang, Ying wrote:
>> Do you have time to take a look at this patch?
>
> Hi Ying, is this handling all places where swapoff might cause a task to read
> invalid data?  For example, why don't other reads of swap_map (for example
> swp_swapcount, page_swapcount, swap_entry_free) need to be synchronized like
> this?

I have checked these places.  They are safe because there are some locks
(like page lock, page table lock, etc.) held to prevent swapoff.  I
found another place in the kernel that is unsafe: the mincore.  I have a
patch for that and will post it (in fact again) after this one is
merged.

Best Regards,
Huang, Ying