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Date:   Wed, 10 Aug 2022 09:03:37 -0700 (PDT)
From:   Hugh Dickins <hughd@google.com>
To:     "Matthew Wilcox (Oracle)" <willy@infradead.org>
cc:     Hugh Dickins <hughd@google.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Zdenek Kabelac <zkabelac@redhat.com>
Subject: Re: [PATCH] shmem: Update folio if shmem_replace_page() updates the
 page
In-Reply-To: <20220730042518.1264767-1-willy@infradead.org>
Message-ID: <9ec4de13-3f7-ba55-924-75d825ec12ed@google.com>
References: <20220730042518.1264767-1-willy@infradead.org>
MIME-Version: 1.0
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Precedence: bulk

On Sat, 30 Jul 2022, Matthew Wilcox (Oracle) wrote:

> If we allocate a new page, we need to make sure that our folio matches
> that new page.  This will be solved by changing shmem_replace_page()
> to shmem_replace_folio(), but this is the minimal fix.
> 
> Fixes: da08e9b79323 ("mm/shmem: convert shmem_swapin_page() to shmem_swapin_folio()")
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Acked-by: Hugh Dickins <hughd@google.com>

I hit this myself just once, at about the very time you sent the fix.
But, thinking that shmem_replace_page() was special for gma500, couldn't
understand how I (or most people) would ever get there.  Turns out that
nowadays tmpfs symlinks longer than 128 can come this way on 32-bit (I
had been testing kmap_local stuff for other reasons).

And today I see that Zdenek hit it on 5.19-rc back in June:
https://lore.kernel.org/lkml/584ae788-05e3-5824-8c85-cbb833677850@redhat.com/
so this patch is definitely one for -stable.

Hugh

> ---
>  mm/shmem.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/shmem.c b/mm/shmem.c
> index a6f565308133..bcc0a3c7b5bf 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1771,6 +1771,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
>  
>  	if (shmem_should_replace_folio(folio, gfp)) {
>  		error = shmem_replace_page(&page, gfp, info, index);
> +		folio = page_folio(page);
>  		if (error)
>  			goto failed;
>  	}
> -- 
> 2.35.1