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Message-ID: <YVT+KWFA8hfSKU+m@casper.infradead.org>
Date: Thu, 30 Sep 2021 01:00:41 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Song Liu <song@...nel.org>
Cc: Rongwei Wang <rongwei.wang@...ux.alibaba.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Linux MM <linux-mm@...ck.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
William Kucharski <william.kucharski@...cle.com>,
Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH v2 1/2] mm, thp: check page mapping when truncating page
cache
On Wed, Sep 29, 2021 at 04:41:48PM -0700, Song Liu wrote:
> The issue is NOT caused by concurrent khugepaged:collapse_file() and
> truncate_pagecache(inode, 0). With some printks, we can see a clear
> time gap (>2 second ) between collapse_file() finishes, and
> truncate_pagecache() (which crashes soon). Therefore, my earlier
> suggestion that adds deny_write_access() to collapse_file() does NOT
> work.
>
> The crash is actually caused by concurrent truncate_pagecache(inode, 0).
> If I change the number of write thread in stress_madvise_dso.c to one,
> (IOW, one thread_read and one thread_write), I cannot reproduce the
> crash anymore.
>
> I think this means we cannot fix this issue in collapse_file(), because it
> finishes long before the crash.
Ah! So are we missing one or more of these locks:
inode_lock(inode);
filemap_invalidate_lock(mapping);
in the open path?
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