linux-kernel - Re: [PATCH] mm/madvise: elevate page refcount while isolating in process

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Message-ID: <297f6c6b-657c-451f-1458-bff96f803c36@quicinc.com>
Date:   Wed, 15 Dec 2021 21:09:57 +0530
From:   Charan Teja Kalla <quic_charante@...cinc.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     <akpm@...ux-foundation.org>, <minchan@...nel.org>,
        <surenb@...gle.com>, <vbabka@...e.cz>, <rientjes@...gle.com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/madvise: elevate page refcount while isolating in
 process_madvise()


On 12/15/2021 7:25 PM, Matthew Wilcox wrote:
> On Wed, Dec 15, 2021 at 05:53:39PM +0530, Charan Teja Reddy wrote:
>> The documentation of isolate_lru_page() says that, "it must be called
>> with an elevated refcount on the page", which is not followed while
>> isolating pages in process_madvise() system call with advise
>> MADV_PAGEOUT. Fix it.
> 
> We hold the mmap_lock over the call to this function, so the reference
> to the page from the page tables cannot go away.  There's no need to
> grab an extra reference here.

Thanks Matthew for clearing such fundamentals.

>