linux-kernel - RE: [PATCH] perf_counter: Fix a race on perf_counter

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: <1250604091.7583.296.camel@twins>
Date:	Tue, 18 Aug 2009 16:01:31 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Metzger, Markus T" <markus.t.metzger@...el.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"hpa@...or.com" <hpa@...or.com>,
	"markus.t.metzger@...il.com" <markus.t.metzger@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>
Subject: RE: [PATCH] perf_counter: Fix a race on perf_counter_ctx

On Tue, 2009-08-18 at 14:54 +0100, Metzger, Markus T wrote:

> Well, that would push out the limit a bit, but it would still be quite fragile.
> 
> Currently, I'm not sure that this (i.e. that the interrupt handling takes too long)
> is the underlying problem of the hangs that I'm seeing.
> 
> If it truly is, then I would go with the two-buffer approach. This would make the
> ISR itself predictably and reliably fast - at the expense of additional locked memory.

comment out that perf_counter_output() call and see what happens ;-)

> Do you think that this truly is the problem?
> How would the kernel react if interrupts were disabled for too long? I would definitely
> expect bad responsiveness, but can the kernel kill itself?

If we're branch tracing while processing the interrupt (not sure here),
then we might well generate enough output to generate a new interrupt,
causing back-to-back interrupts, basically DoSing the machine.


--
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/