From: Andrew Morton <akpm@linux-foundation.org>
To: Rongwei Wang <rongwei.wang@linux.alibaba.com>
Cc: Matthew Wilcox <willy@infradead.org>,
Linux MM <linux-mm@kvack.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
song@kernel.org, william.kucharski@oracle.com,
Hugh Dickins <hughd@google.com>
Subject: Re: [PATCH v2 1/2] mm, thp: check page mapping when truncating page cache
Date: Thu, 23 Sep 2021 19:43:43 -0700 [thread overview]
Message-ID: <20210923194343.ca0f29e1c4d361170343a6f2@linux-foundation.org> (raw)
In-Reply-To: <BC145393-93AC-4DF4-9CF4-2FB1C736B70C@linux.alibaba.com>
On Thu, 23 Sep 2021 01:04:54 +0800 Rongwei Wang <rongwei.wang@linux.alibaba.com> wrote:
>
>
> > On Sep 22, 2021, at 7:37 PM, Matthew Wilcox <willy@infradead.org> wrote:
> >
> > 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.
> Hi, Matthew
> I am not sure get your means. We know “mm, thp: relax the VM_DENYWRITE constraint on file-backed THPs"
> Introduced file-backed THPs for DSO. It is possible {very rarely} for DSO to be opened in writeable way.
>
> ...
>
> > https://lore.kernel.org/linux-mm/YUdL3lFLFHzC80Wt@casper.infradead.org/
> All in all, what you mean is that we should solve this race at the source?
Matthew is being pretty clear here: we shouldn't be permitting
userspace to get a writeable fd for a thp-backed file.
Why are we permitting the DSO to be opened writeably? If there's a
legitimate case for doing this then presumably "mm, thp: relax the
VM_DENYWRITE constraint on file-backed THPs: should be fixed or
reverted.
If there is no legitimate use case for returning a writeable fd for a
thp-backed file then we should fail such an attempt at open(). This
approach has back-compatibility issues which need to be thought about.
Perhaps we should permit the open-writeably attempt to appear to
succeed, but to really return a read-only fd?
next prev parent reply other threads:[~2021-09-24 2:43 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-06 12:11 [PATCH 0/2] mm, thp: fix file-backed THP race in collapse_file Rongwei Wang
2021-09-06 12:11 ` [PATCH 1/2] mm, thp: check page mapping when truncating page cache Rongwei Wang
2021-09-07 2:49 ` Yu Xu
2021-09-07 18:08 ` Yang Shi
[not found] ` <38AF4DC8-5E6F-4568-B2E3-0434BD847BC9@linux.alibaba.com>
2021-09-08 21:48 ` Yang Shi
2021-09-13 14:49 ` [mm, thp] 20753096b6: BUG:unable_to_handle_page_fault_for_address kernel test robot
2021-09-06 12:12 ` [PATCH 2/2] mm, thp: bail out early in collapse_file for writeback page Rongwei Wang
2021-09-07 16:56 ` Yang Shi
[not found] ` <44BE85B4-692C-41E8-B5A0-C1E0B0272ACD@linux.alibaba.com>
2021-09-08 21:51 ` Yang Shi
2021-09-22 7:06 ` [PATCH v2 0/2] mm, thp: fix file-backed THP race in collapse_file and truncate pagecache Rongwei Wang
2021-09-22 7:06 ` [PATCH v2 1/2] mm, thp: check page mapping when truncating page cache Rongwei Wang
2021-09-22 11:37 ` Matthew Wilcox
2021-09-22 17:04 ` Rongwei Wang
2021-09-24 2:43 ` Andrew Morton [this message]
2021-09-24 3:08 ` Yang Shi
2021-09-24 3:35 ` Rongwei Wang
2021-09-24 7:12 ` Rongwei Wang
2021-09-27 22:24 ` Song Liu
2021-09-28 12:06 ` Matthew Wilcox
2021-09-28 16:59 ` Song Liu
2021-09-28 16:20 ` Rongwei Wang
2021-09-29 7:14 ` Song Liu
2021-09-29 7:50 ` Rongwei Wang
2021-09-29 16:59 ` Song Liu
2021-09-29 17:55 ` Matthew Wilcox
2021-09-29 23:41 ` Song Liu
2021-09-30 0:00 ` Matthew Wilcox
2021-09-30 0:41 ` Song Liu
2021-09-30 2:14 ` Rongwei Wang
2021-10-04 17:26 ` Rongwei Wang
2021-10-04 19:05 ` Matthew Wilcox
2021-10-05 1:58 ` Rongwei Wang
2021-10-04 20:26 ` Song Liu
2021-10-05 2:58 ` Hugh Dickins
2021-10-05 3:07 ` Matthew Wilcox
2021-10-05 9:03 ` Rongwei Wang
2021-09-30 1:54 ` Rongwei Wang
2021-09-30 3:26 ` Song Liu
2021-09-30 5:24 ` Hugh Dickins
2021-09-30 15:28 ` Matthew Wilcox
2021-09-30 16:49 ` Hugh Dickins
2021-09-30 17:39 ` Yang Shi
2021-10-02 17:08 ` Matthew Wilcox
2021-10-04 18:28 ` Yang Shi
2021-10-04 19:31 ` Matthew Wilcox
2021-10-05 2:26 ` Hugh Dickins
2021-10-02 2:22 ` Rongwei Wang
2021-09-22 7:06 ` [PATCH v2 2/2] mm, thp: bail out early in collapse_file for writeback page Rongwei Wang
2021-10-06 2:18 ` [PATCH v3 v3 0/2] mm, thp: fix file-backed THP race in collapse_file and truncate pagecache Rongwei Wang
2021-10-06 2:18 ` [PATCH v3 v3 1/2] mm, thp: lock filemap when truncating page cache Rongwei Wang
2021-10-06 2:18 ` [PATCH v3 v3 2/2] mm, thp: bail out early in collapse_file for writeback page Rongwei Wang
2021-10-06 2:41 ` Matthew Wilcox
2021-10-06 8:39 ` Rongwei Wang
2021-10-06 17:58 ` Yang Shi
2021-10-11 2:22 ` [PATCH v4 0/2] mm, thp: fix file-backed THP race in collapse_file and truncate pagecache Rongwei Wang
2021-10-11 2:22 ` [PATCH v4 1/2] mm, thp: lock filemap when truncating page cache Rongwei Wang
2021-10-13 7:55 ` Rongwei Wang
2021-10-11 2:22 ` [PATCH v4 2/2] mm, thp: bail out early in collapse_file for writeback page Rongwei Wang
2021-10-11 3:08 ` Matthew Wilcox
2021-10-11 3:22 ` Rongwei Wang
2021-10-11 5:08 ` [PATCH v4 RESEND " Rongwei Wang
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