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Date:   Thu, 18 Mar 2021 12:16:14 +0000
From:   Luis Henriques <lhenriques@suse.de>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Miklos Szeredi <miklos@szeredi.hu>,
        Vlastimil Babka <vbabka@suse.cz>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm <linux-mm@kvack.org>
Subject: Re: fuse: kernel BUG at mm/truncate.c:763!
Message-ID: <YFNEjnjF+RujYOL0@suse.de>
References: <CAJfpegu+T-4m=OLMorJrZyWaDNff1eviKUaE2gVuMmLG+g9JVQ@mail.gmail.com>
 <YEtc54pWLLjb6SgL@suse.de>
 <20210312131123.GZ3479805@casper.infradead.org>
 <YE8tQc66C6MW7EqY@suse.de>
 <20210315110659.GT2577561@casper.infradead.org>
 <YFMct4z1gEa8tXkh@suse.de>
 <CAJfpeguX7NrdTH4JLbCtkQ1u7TFvUh+8s7RmwB_wmuPHJsQyiA@mail.gmail.com>
 <20210318110302.nxddmrhmgmlw4adq@black.fi.intel.com>
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 <20210318115543.GM3420@casper.infradead.org>
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On Thu, Mar 18, 2021 at 11:55:43AM +0000, Matthew Wilcox wrote:
> On Thu, Mar 18, 2021 at 11:29:28AM +0000, Luis Henriques wrote:
> > On Thu, Mar 18, 2021 at 02:03:02PM +0300, Kirill A. Shutemov wrote:
> > > On Thu, Mar 18, 2021 at 11:59:59AM +0100, Miklos Szeredi wrote:
> > > > > [16247.536348] page:00000000dfe36ab1 refcount:673 mapcount:0 mapping:00000000f982a7f8 index:0x1400 pfn:0x4c65e00
> > > > > [16247.536359] head:00000000dfe36ab1 order:9 compound_mapcount:0 compound_pincount:0
> > > > 
> > > > This is a compound page alright.   Have no idea how it got into fuse's
> > > > pagecache.
> > > 
> > > 
> > > Luis, do you have CONFIG_READ_ONLY_THP_FOR_FS enabled?
> > 
> > Yes, it looks like Tumbleweed kernels have that config option enabled by
> > default.  And it this feature was introduced in 5.4 (the bug doesn't seem
> > to be reproducible in 5.3).
> 
> Can you try adding this patch?
> 
> https://git.infradead.org/users/willy/pagecache.git/commitdiff/369a4fcd78369b7a026bdef465af9669bde98ef4

Yep, sure.  Unfortunately, the testing round-trip can be a bit high.  I'll
push a new kernel build and ask the reporter to give it a try.

[ I'll add this patch on top of the s/BUG_ON/VM_BUG_ON_PAGE change. ]

Cheers,
--
Lu?s