linux-kernel - Re: [RFC][PATCH 2/6] lockdep: validate rcu_dereference() vs rcu_read

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20070919221349.2935f69d@lappy>
Date:	Wed, 19 Sep 2007 22:13:49 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	"Dmitry Torokhov" <dmitry.torokhov@...il.com>
Cc:	paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	"Ingo Molnar" <mingo@...e.hu>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Nick Piggin" <nickpiggin@...oo.com.au>
Subject: Re: [RFC][PATCH 2/6] lockdep: validate rcu_dereference() vs
 rcu_read_lock()

On Wed, 19 Sep 2007 15:49:24 -0400 "Dmitry Torokhov"
<dmitry.torokhov@...il.com> wrote:

> On 9/19/07, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> > On Wed, 19 Sep 2007 14:49:56 -0400 "Dmitry Torokhov"
> > <dmitry.torokhov@...il.com> wrote:
> >
> > > On 9/19/07, Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:
> >
> > > > PS to previous -- any problem with inserting rcu_read_lock() and
> > > > rcu_read_unlock() around the portion of the IRQ handler that has
> > > > these accesses?
> > > >
> > >
> > > I guess I could but it is an extra lock that needs to be managed and
> > > given the fact that it is not really needed (other to make a newly
> > > developed tool happy) I am hestsant to do that.
> >
> > As is, these sites are a bug in -rt and we'll need to fix them anyway.
> >
> > As for the code you pointed me to, the i8042 driver, it seems to play
> > way to funny tricks for a simple 'slow' driver.
> 
> Even "slow" driver should try not to slow down the rest of the system
> if it can help it. I am sorry if the thing it does do not quite fit in
> with the changes you are proposing but it does not make the exeisting
> code invalid.
> 
> >
> > If you replace the spin_lock() + sync_sched(), with rcu_read_lock() +
> > rcu_call() it should work again without adding an extra lock.
> >
> 
> Except that I need spin_lock_irq for other reasons. I could take the
> same lock in write-side code and not use RCU at all but using RCU
> allows opening/closing input devices without slowing down interrupt
> handlers so why not use it?

If the IRQ handler does rcu_read_lock(),unlock() and the i8042_stop()
function does sync_rcu() instead of _sched(), it should be good again.
It will not affect anything else than the task that calls _stop(). And
even there the only change is that the sleep might be a tad longer.

I find it curious that a driver that is 'low performant' and does not
suffer lock contention pioneers locking schemes. I agree with
optimizing, but this is not the place to push the envelope.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/