linux-kernel - Re: lock classes

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Message-ID: <6be3513e-67d8-4ead-b44a-e6dcdedfeaab@paulmck-laptop>
Date: Mon, 1 Jul 2024 09:20:02 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: ahmed Ehab <bottaawesome633@...il.com>
Cc: boqun.feng@...il.com, linux-kernel@...r.kernel.org
Subject: Re: lock classes

On Mon, Jul 01, 2024 at 03:52:44AM +0300, ahmed Ehab wrote:
> Hello sir,
> I am working on a bug reported by syzkaller
> https://syzkaller.appspot.com/bug?extid=d4200fc83fa03a684c6e . I am getting
> 2 classes with the same key but different address for the name(different
> name pointer but same content). The problem is that this info seems to be
> persisted in the vmlinux itself. Is there any place where I can read about
> how lock classes are persisted or something?

Hello, Ahmed,

Adding Boqun and the list on CC in case others have better advice.

One possibility is that there is a lockdep_set_class_and_name() call
that is separating out locks that would by default be in the same
class.  See the use of this function in the rcu_init_one() function in
kernel/rcu/tree.c for one example use, in this case to create separate
lock classes for each level of the rcu_node tree.

There are a number of similar functions, including lockdep_set_class()
and lockdep_set_class_and_subclass().  These guys might well duplicate
the name, but I have never used them.  Me, I encode the level into
the name in order to have better lockdep diagnostics, but that is not
always practical.

							Thanx, Paul