linux-kernel - Re: [PATCH v2 1/2] mm, thp: check page mapping when truncating page cache

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Date:   Wed, 22 Sep 2021 12:37:20 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Rongwei Wang <rongwei.wang@...ux.alibaba.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org, cfijalkovich@...gle.com,
        song@...nel.org, william.kucharski@...cle.com, hughd@...gle.com
Subject: Re: [PATCH v2 1/2] mm, thp: check page mapping when truncating page
 cache

On Wed, Sep 22, 2021 at 03:06:44PM +0800, Rongwei Wang wrote:
> Transparent huge page has supported read-only non-shmem files. The file-
> backed THP is collapsed by khugepaged and truncated when written (for
> shared libraries).
> 
> However, there is race in two possible places.
> 
> 1) multiple writers truncate the same page cache concurrently;
> 2) collapse_file rolls back when writer truncates the page cache;

As I've said before, the bug here is that somehow there is a writable fd
to a file with THPs.  That's what we need to track down and fix.

https://lore.kernel.org/linux-mm/YUdL3lFLFHzC80Wt@casper.infradead.org/