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

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Date:   Wed, 15 Dec 2021 13:55:35 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Charan Teja Reddy <quic_charante@...cinc.com>
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 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.