linux-kernel - Re: BUG: using smp_processor_id() in preemptible [00000000] code: icedove-bin/5449

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: <1274942798.27810.3584.camel@twins>
Date:	Thu, 27 May 2010 08:46:38 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	piotr@...owicz.com, linux-kernel@...r.kernel.org,
	Jens Axboe <jens.axboe@...cle.com>,
	Divyesh Shah <dpshah@...gle.com>
Subject: Re: BUG: using smp_processor_id() in preemptible [00000000] code:
 icedove-bin/5449

On Wed, 2010-05-26 at 16:02 -0700, Andrew Morton wrote:

> How is anyone supposed to use this?  What are the semantics of this
> thing?  What are the units of its return value?  What is the base value
> of its return value?  Does it return different times on different CPUs?
> I assume so, otherwise why does sched_clock_cpu() exist?  <looks at
> the sched_clock_cpu() documentation, collapses in giggles>

The point of the whole sched_clock_cpu() thing is to provide a fairly
high resolution clock with bounded drift between cpus.

It also promises to be monotonic per cpu argument, that is,
sched_clock_cpu(j) will, for a constant j always return a monotonic
increasing timestamp.

It doesn't make much promises about its base (although people tend to
want it to start at 0 on boot, but the users really shouldn't care).

sched_clock() doesn't promise either bounded drift between cpus nor
monotonicity.

--
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/