Message-ID: <009501c4d4c6$40b4f270$6400a8c0@centrino>
From: "Bernard Normier" <bernard@zeroc.com>
To: "Jan Engelhardt" <jengelh@linux01.gwdg.de>
Cc: <linux-kernel@vger.kernel.org>
References: <006001c4d4c2$14470880$6400a8c0@centrino> <Pine.LNX.4.53.0411272154560.6045@yvahk01.tjqt.qr>
Subject: Re: Concurrent access to /dev/urandom
Date: Sat, 27 Nov 2004 16:15:36 -0500
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> >As long as I serialize access to /dev/urandom, I get different values.
>>However, with concurrent access to /dev/urandom, I quickly get duplicate
>
> How do you concurrently read from urandom? That's only possible with 2 or 
> more
> CPUs, and even then, I hope that the urandom chardev has some spinlock.
>
As shown in the code included in my first e-mail, each thread simply
open("/dev/urandom", O_RDONLY), use read(2) to read 16 bytes, and
then close the file descriptor.
Duplicates appear quickly on: single CPU with HT, dual CPU without HT,
and dual CPU with HT (all with smp kernels)
But not on a lower end single CPU without HT (2.6.8-1.521 non-smp).

>>#include <pthread.h>
>>[...]
>
> Rule of thumb: Post the smallest possible code that shows the problem.
Will do next time!

Bernard


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