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From:   "Huang\, Ying" <ying.huang@intel.com>
To:     Daniel Jordan <daniel.m.jordan@oracle.com>
Cc:     Andrea Arcangeli <aarcange@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
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Subject: Re: [PATCH -mm -V8] mm, swap: fix race between swapoff and some swap operations
References: <20190218070142.5105-1-ying.huang@intel.com>
        <87mumjt57i.fsf@yhuang-dev.intel.com>
        <20190226230729.bz2ukzlub3rbdoqp@ca-dmjordan1.us.oracle.com>
Date:   Wed, 27 Feb 2019 09:13:14 +0800
In-Reply-To: <20190226230729.bz2ukzlub3rbdoqp@ca-dmjordan1.us.oracle.com>
        (Daniel Jordan's message of "Tue, 26 Feb 2019 18:07:29 -0500")
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Daniel Jordan <daniel.m.jordan@oracle.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