linux-kernel - Re: [REGRESSION][BISECTED] Crash with Bad page state for FUSE/Flatpak related applications since v6.13

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Message-ID: <Z6ct4bEdeZwmksxS@casper.infradead.org>
Date: Sat, 8 Feb 2025 10:11:45 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Joanne Koong <joannelkoong@...il.com>
Cc: Vlastimil Babka <vbabka@...e.cz>, Josef Bacik <josef@...icpanda.com>,
	Miklos Szeredi <miklos@...redi.hu>,
	Christian Heusel <christian@...sel.eu>,
	Miklos Szeredi <mszeredi@...hat.com>, regressions@...ts.linux.dev,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm <linux-mm@...ck.org>,
	Mantas Mikulėnas <grawity@...il.com>
Subject: Re: [REGRESSION][BISECTED] Crash with Bad page state for
 FUSE/Flatpak related applications since v6.13

On Fri, Feb 07, 2025 at 04:22:56PM -0800, Joanne Koong wrote:
> > Thanks, Josef. I guess we can at least try to confirm we're on the right track.
> > Can anyone affected see if this (only compile tested) patch fixes the issue?
> > Created on top of 6.13.1.
> 
> This fixes the crash for me on 6.14.0-rc1. I ran the repro using
> Mantas's instructions for Obfuscate. I was able to trigger the crash
> on a clean build and then with this patch, I'm not seeing the crash
> anymore.

Since this patch fixes the bug, we're looking for one call to folio_put()
too many.  Is it possibly in fuse_try_move_page()?  In particular, this
one:

        /* Drop ref for ap->pages[] array */
        folio_put(oldfolio);

I don't know fuse very well.  Maybe this isn't it.