From: "Theodore Ts'o" <tytso@mit.edu>
To: Alexander Lochmann <alexander.lochmann@tu-dortmund.de>
Cc: Horst Schirmeier <horst.schirmeier@tu-dortmund.de>,
Jan Kara <jack@suse.cz>, Jan Kara <jack@suse.com>,
linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC] inode.i_opflags - Usage of two different locking schemes
Date: Fri, 5 Mar 2021 10:18:16 -0500 [thread overview]
Message-ID: <YEJLuP6+Zy8/dq+D@mit.edu> (raw)
In-Reply-To: <a4709bc4-ee62-2cdc-0628-32e8fa73e8f9@tu-dortmund.de>
On Fri, Mar 05, 2021 at 02:10:09PM +0100, Alexander Lochmann wrote:
> Hi folks,
>
> I've stumbled across an interesting locking scheme. It's related to struct
> inode, more precisely it is an mqueue inode.
> Our results show that inode:mqueue.i_opflags is read with i_rwsem being
> hold.
> In d_flags_for_inode, and do_inode_permission the i_lock is used to read and
> write i_opflags.
> Is this a real locking scheme? Is a lock needed to access i_opflags at all?
> What is the magic behind this contradiction?
>
> I've put the report of the counterexamples on our webserver:
> https://ess.cs.tu-dortmund.de/lockdoc-bugs/cex-inode-mqueue.html.
> It contains the stacktraces leading to those accesses, and the locks that
> were actually held.
1) I don't see where i_opflags is being read in ipc/mqueue.c at all,
either with or without i_rwsem.
2) I'm not sure what this has to do with ext4?
- Ted
next prev parent reply other threads:[~2021-03-05 15:19 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <f63dd495-defb-adc4-aa91-6aacd7f441c7@tu-dortmund.de>
2021-03-05 13:10 ` [RFC] inode.i_opflags - Usage of two different locking schemes Alexander Lochmann
2021-03-05 15:18 ` Theodore Ts'o [this message]
2021-03-05 15:35 ` Alexander Lochmann
2021-03-05 16:04 ` Theodore Ts'o
2021-03-08 14:05 ` Alexander Lochmann
2021-03-16 17:14 ` Jan Kara
2021-03-26 16:37 ` Alexander Lochmann
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