linux-kernel - Re: [RFC PATCH] fs/buffer: Handle non folio buffer case for drop

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Message-ID: <aAvqAMBW7fzYkz_o@casper.infradead.org>
Date: Fri, 25 Apr 2025 21:01:04 +0100
From: Matthew Wilcox <willy@...radead.org>
To: I Hsin Cheng <richard120310@...il.com>
Cc: Jan Kara <jack@...e.cz>,
	syzbot+de1498ff3a934ac5e8b4@...kaller.appspotmail.com,
	viro@...iv.linux.org.uk, brauner@...nel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	jfs-discussion@...ts.sourceforge.net, shaggy@...nel.org,
	syzkaller-bugs@...glegroups.com, skhan@...uxfoundation.org,
	linux-kernel-mentees@...ts.linux.dev
Subject: Re: [RFC PATCH] fs/buffer: Handle non folio buffer case for
 drop_buffer()

On Sat, Apr 26, 2025 at 12:52:42AM +0800, I Hsin Cheng wrote:
> > Can you print more about the folio where this happened? In particular it
> > would be interesting what's in folio->flags, folio->mapping->flags and
> > folio->mapping->aops (resolved to a symbol). Because either the mapping has
> > AS_RELEASE_ALWAYS set but then we should have ->releasepage handler, or
> > have PG_Private bit set without buffers attached to a page but then again
> > either ->releasepage should be set or there's some bug in fs/buffer.c which
> > can set PG_Private without attaching buffers (I don't see where that could
> > be).
> > 
> 
> Hmm so I suppose when there're buffers attached, the PG_Private bit
> should always be set in folio->flags or folio->mapping->flags or
> folio->mapping->aops ?

See folio_attach_private().  I am trying to get rid of PG_private, but
we're not quite there yet.  The other information may help track down
what is going on.