linux-kernel - Re: [local DoS] Re: Linux 2.6.24-rc4

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Message-ID: <20071204140425.05b0b458@mandriva.com.br>
Date:	Tue, 4 Dec 2007 14:04:25 -0200
From:	"Luiz Fernando N. Capitulino" <lcapitulino@...driva.com.br>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	herton@...driva.com.br, dvgevers@...all.nl
Subject: Re: [local DoS] Re: Linux 2.6.24-rc4

Em Tue, 4 Dec 2007 17:00:05 +0100
Ingo Molnar <mingo@...e.hu> escreveu:

| 
| * Linus Torvalds <torvalds@...ux-foundation.org> wrote:
| 
| > 
| > 
| > On Tue, 4 Dec 2007, Luiz Fernando N. Capitulino wrote:
| > >
| > > 	sched_rr_get_interval(1, NULL);
| > 
| > Looks like we have a zero "cfs_rq->load.weight".
| > 
| > Ingo? Both sched_slice() and __sched_slice() do a divide by the 
| > runqueue weight, and at least dequeue_task_fair() explicitly checks 
| > for that being zero, so clearly zero is a possible value. Hmm?
| 
| yeah, i can reproduce this crash too.
| 
| The problem is on SMP: if sched_rr_get_interval() gets a task from an 
| otherwise idle runqueue, then rq->load.weight is 0. Normally 
| sched_slice() is only used on a busy runqueue. So the correct fixup site 
| is not in sched_slice() but in sys_sched_rr_get_interval() - i'm working 
| on the right fix, i hope to be able to send a pull request in a few 
| minutes.

 Ingo, I can reproduce this w/o SMP support as well.

 (Also, the backtrace I sent was reproduced on a UP machine with a
SMP kernel).

-- 
Luiz Fernando N. Capitulino
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