From: Hugh Dickins <hughd@google.com>
To: Rongwei Wang <rongwei.wang@linux.alibaba.com>
Cc: Song Liu <song@kernel.org>, Matthew Wilcox <willy@infradead.org>,
Hugh Dickins <hughd@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linux MM <linux-mm@kvack.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
William Kucharski <william.kucharski@oracle.com>
Subject: Re: [PATCH v2 1/2] mm, thp: check page mapping when truncating page cache
Date: Mon, 4 Oct 2021 19:58:10 -0700 (PDT) [thread overview]
Message-ID: <d2776967-bb9f-985b-6d38-d1d1dc83cd7b@google.com> (raw)
In-Reply-To: <8d8fb192-bd8d-8a08-498d-ca7204d4a716@linux.alibaba.com>
On Tue, 5 Oct 2021, Rongwei Wang wrote:
> Hi,
> I have run our cases these two days to stress test new Patch #1. The new Patch
> #1 mainly add filemap_invalidate_{un}lock before and after
> truncate_pagecache(), basing on original Patch #1. And the crash has not
> happened.
>
> Now, I keep the original Patch #1, then adding the code below which suggested
> by liu song (I'm not sure which one I should add in the next version,
> Suggested-by or Signed-off-by? If you know, please remind me).
>
> - if (filemap_nr_thps(inode->i_mapping))
> + if (filemap_nr_thps(inode->i_mapping)) {
> + filemap_invalidate_lock(inode->i_mapping);
> truncate_pagecache(inode, 0);
> + filemap_invalidate_unlock(inode->i_mapping);
> + }
I won't NAK that patch; but I still believe it's unnecessary, and don't
see how it protects against all the races (collapse_file() does not use
that lock, whereas collapse_file() does use page lock). And if you're
hoping to fix 5.10, then you will have to backport those invalidate_lock
patches there too (they're really intended to protect hole-punching).
>
> And the reason for keeping the original Patch #1 is mainly to fix the race
> between collapse_file and truncate_pagecache. It seems necessary. Despite the
> two-day test, I did not reproduce this race any more.
>
> In addition, I also test the below method:
>
> diff --git a/mm/truncate.c b/mm/truncate.c
> index 3f47190f98a8..33604e4ce60a 100644
> --- a/mm/truncate.c
> +++ b/mm/truncate.c
> @@ -210,8 +210,6 @@ invalidate_complete_page(struct address_space *mapping,
> struct page *page)
>
> int truncate_inode_page(struct address_space *mapping, struct page *page)
> {
> - VM_BUG_ON_PAGE(PageTail(page), page);
> -
> if (page->mapping != mapping)
> return -EIO;
>
> I am not very sure this VM_BUG_ON_PAGE(PageTail) is what Hugh means. And
> the test results show that only removing this VM_BUG_ON_PAGE(PageTail) has no
> effect. So, I still keep the original Patch #1 to fix one race.
Yes, that's exactly what I meant, and thank you for intending to try it.
But if that patch had "no effect", then I think you were not running the
kernel with that patch applied: because it deletes the BUG on line 213
of mm/truncate.c, which is what you reported in the first mail!
Or, is line 213 of mm/truncate.c in your 5.10.46-hugetext+ kernel
something else? I've been looking at 5.15-rc.
But I wasn't proposing to delete it merely to hide the BUG: as I hope
I explained, we could move it below the page->mapping check, but it
wouldn't really be of any value there since tails have NULL page->mapping
anyway (well, I didn't check first and second tails, maybe mapping gets
reused for some compound page field in those). I was proposing to delete
it because the page->mapping check then weeds out the racy case once
we're holding page lock, without the need for adding anything special.
Hugh
next prev parent reply other threads:[~2021-10-05 2:58 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
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 [this message]
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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