linux-kernel - Re: [pchecks v2 2/2] percpu: Add preemption checks to __this

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]

Date:	Fri, 4 Oct 2013 18:52:22 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Tejun Heo <tj@...nel.org>, akpm@...uxfoundation.org,
	Steven Rostedt <srostedt@...hat.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [pchecks v2 2/2] percpu: Add preemption checks to __this_cpu ops

On Fri, Oct 04, 2013 at 03:27:15PM +0000, Christoph Lameter wrote:
> On Fri, 4 Oct 2013, Peter Zijlstra wrote:
> 
> > > -# define __this_cpu_read(pcp)	__pcpu_size_call_return(__this_cpu_read_, (pcp))
> > > +# define __this_cpu_read(pcp) \
> > > +	(__this_cpu_preempt_check(),__pcpu_size_call_return(__this_cpu_read_, (pcp)))
> > >  #endif
> >
> > Would it not be move convenient to implement it in terms of the
> > raw_this_cpu*() thingies? That way you're sure they actually do the same
> > thing and there's only 1 site to change when changing the
> > implementation.
> 
> The __this_cpu_read_xxx() are asm primitives provided by various arches.
> __this_cpu_read() is currently not overriden by any arches. That is why
> the approach here of replicating only the higher level for raw_cpu_ops
> works. Renaming the __this_cpu_xxx primitives would be a significant
> change.

This isn't about read; this is about all of them. Make sure the raw_*
implementation is the actual real implementation; then implement the
checking variant in terms of those.

> > >  	if (!printk_ratelimit())
> > >  		goto out_enable;
> > >
> > > -	printk(KERN_ERR "BUG: using smp_processor_id() in preemptible [%08x] "
> > > -			"code: %s/%d\n",
> > > +	printk(KERN_ERR "%s in preemptible [%08x] "
> > > +			"code: %s/%d\n", what,
> > >  			preempt_count() - 1, current->comm, current->pid);
> >
> > I would argue for keeping the "BUG" string intact and in front of the
> > %s.
> 
> Most of the place that I have seen are not bugs but there was a
> reason for the code to run a __this_cpu op without preemption disabled.

No; it is an actual BUG; it means that whoemever wrote the code didn't
think straight and forgot to use the right primitive and comments.
--
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/