linux-kernel - Re: [PATCH 1/1] lockdep: Kill held_lock->check and "int check" arg of __lock

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Date:	Mon, 13 Jan 2014 19:52:38 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/1] lockdep: Kill held_lock->check and "int check" arg
	of __lock_acquire()

On 01/13, Peter Zijlstra wrote:
>
> On Mon, Jan 13, 2014 at 06:06:09PM +0100, Oleg Nesterov wrote:
> >
> > And I just realized that rcu_lock_acquire() does lock_acquire(check => 1).
> > Probably we can mark rcu_lock_map's as __lockdep_no_validate__.
>
> Can't, RCU needs its own classes. Otherwise it cannot tell which version
> of the RCU read lock its holding at just that moment.

Ah, indeed. Thanks.

Can't it do lock_acquire(trylock => 1, read => 2) ? this still means
mark_irqflags(), but perhaps this won't hurt too much.

> At the very least we can reduce check to a single bit.

Or this, yes.

Oleg.

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