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From: Roman Smirnov <r.smirnov@omp.ru>
To: Matthew Wilcox <willy@infradead.org>
CC: "stable@vger.kernel.org" <stable@vger.kernel.org>, Greg Kroah-Hartman
	<gregkh@linuxfoundation.org>, Andrew Morton <akpm@linux-foundation.org>,
	Alexey Khoroshilov <khoroshilov@ispras.ru>, Sergey Shtylyov
	<s.shtylyov@omp.ru>, Karina Yankevich <k.yankevich@omp.ru>,
	"lvc-project@linuxtesting.org" <lvc-project@linuxtesting.org>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: Re: [PATCH 5.10 0/2] mm/truncate: fix issue in ext4_set_page_dirty()
Thread-Topic: [PATCH 5.10 0/2] mm/truncate: fix issue in ext4_set_page_dirty()
Thread-Index: AQHaRJvZs/ufXYdw80SbjgapkLNiNLDUiucAgAGlSY4=
Date: Fri, 12 Jan 2024 13:40:17 +0000
Message-ID: <3cd52f6e1b3d4daba35fb350e990e646@omp.ru>
References: <20240111143747.4418-1-r.smirnov@omp.ru>,<ZaAJwEg4rvleFuC9@casper.infradead.org>
In-Reply-To: <ZaAJwEg4rvleFuC9@casper.infradead.org>
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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=20
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.