From: Alexander Lochmann <alexander.lochmann@tu-dortmund.de>
To: Horst Schirmeier <horst.schirmeier@tu-dortmund.de>,
Jan Kara <jack@suse.cz>, "Theodore Ts'o" <tytso@mit.edu>,
Jan Kara <jack@suse.com>,
linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [RFC] inode.i_opflags - Usage of two different locking schemes
Date: Fri, 5 Mar 2021 14:10:09 +0100 [thread overview]
Message-ID: <a4709bc4-ee62-2cdc-0628-32e8fa73e8f9@tu-dortmund.de> (raw)
In-Reply-To: <f63dd495-defb-adc4-aa91-6aacd7f441c7@tu-dortmund.de>
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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.
Regards,
Alex
--
Technische Universität Dortmund
Alexander Lochmann PGP key: 0xBC3EF6FD
Otto-Hahn-Str. 16 phone: +49.231.7556141
D-44227 Dortmund fax: +49.231.7556116
http://ess.cs.tu-dortmund.de/Staff/al
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next parent reply other threads:[~2021-03-05 13:11 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 ` Alexander Lochmann [this message]
2021-03-05 15:18 ` [RFC] inode.i_opflags - Usage of two different locking schemes Theodore Ts'o
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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