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

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Date:   Mon, 4 Oct 2021 20:05:11 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Rongwei Wang <rongwei.wang@...ux.alibaba.com>
Cc:     Song Liu <song@...nel.org>, Hugh Dickins <hughd@...gle.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>
Subject: Re: [PATCH v2 1/2] mm, thp: check page mapping when truncating page
 cache

On Tue, Oct 05, 2021 at 01:26:50AM +0800, 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.

You shouldn't need most of patch 1.

In fact, the only two patches you should need would be this:

+++ b/mm/filemap.c
@@ -2093,7 +2093,6 @@ unsigned find_lock_entries(struct address_space *mapping, pgoff_t start,
                if (!xa_is_value(page)) {
                        if (page->index < start)
                                goto put;
-                       VM_BUG_ON_PAGE(page->index != xas.xa_index, page);
                        if (page->index + thp_nr_pages(page) - 1 > end)
                                goto put;
                        if (!trylock_page(page))

(already in Andrew's tree) and:

> -               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);
> +               }

If you can still hit a bug with just those two patches, then something
else is going wrong, and needs to be investigated.