linux-kernel - High Resolution Timer DOS

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-next>] [day] [month] [year] [list]

Message-ID: <4633C269.9050806@free.fr>
Date:	Sat, 28 Apr 2007 23:53:45 +0200
From:	matthieu castet <castet.matthieu@...e.fr>
To:	Linux Kernel list <linux-kernel@...r.kernel.org>
Subject: High Resolution Timer DOS

Hi,

some programs need to do some short of busyloop. It was often 
implemented as :

while (1) {
	if (can_do_stuff) {
		do_stuff();
	}
	else
		//sleep a very short of time
		usleep(1);
}

usleep(1) or equivalent where used instead of sched_yield, because of 
some priority issue. IIRC doing sched_yield, make the process appears 
like an interactive process, so it has better priority and get call more 
often.

But now if high res timer are enabled, these programs while cause 
something like a DOS : the context switch per second will be bigger than 
500 000 and the cpu usage will be very high.

I don't know if such problem are already know, but I believe a warning 
about such issues should be in the Kconfig description.

Matthieu
-
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/