linux-kernel - Re: [PATCH 5.10 0/2] mm/truncate: fix issue in ext4_set_page

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Message-ID: <3cd52f6e1b3d4daba35fb350e990e646@omp.ru>
Date: Fri, 12 Jan 2024 13:40:17 +0000
From: Roman Smirnov <r.smirnov@....ru>
To: Matthew Wilcox <willy@...radead.org>
CC: "stable@...r.kernel.org" <stable@...r.kernel.org>, Greg Kroah-Hartman
	<gregkh@...uxfoundation.org>, Andrew Morton <akpm@...ux-foundation.org>,
	Alexey Khoroshilov <khoroshilov@...ras.ru>, Sergey Shtylyov
	<s.shtylyov@....ru>, Karina Yankevich <k.yankevich@....ru>,
	"lvc-project@...uxtesting.org" <lvc-project@...uxtesting.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 5.10 0/2] mm/truncate: fix issue in ext4_set_page_dirty()

On Thu, 11 Jan 2024 15:31:12 +0000, Matthew Wilcox wrote:

> I do not understand the crash, and I do not understand why this patch
> would fix it.  Can you explain either?

The WARNING appears in the following location:
https://elixir.bootlin.com/linux/v5.10.205/source/fs/ext4/inode.c#L3693

Reverse bisection pointed at the 2nd patch as a fix, but after 
backporting this patch to 5.10 branch I still hit the WARNING.
I noticed that there was some missing code compared to the original
patch:

if (folio_has_private(folio) && !filemap_release_folio(folio, 0))
         return 0;

Then I found a patch with this code before using folio, applied it,
and tests showed the WARNING disappeared. I also used the linux test
project to make sure nothing was broken. I'll try to dig a little
deeper and explain the crash.

Thanks for the reply.