From: Andi Kleen <ak@suse.de>
To: Eric Dumazet <dada1@cosmosbay.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] [RFC] Optimize select/poll by putting small data sets on the stack
Date: Wed, 4 Jan 2006 01:48:42 +0100 [thread overview]
Message-ID: <200601040148.42765.ak@suse.de> (raw)
In-Reply-To: <43BB1A29.7090102@cosmosbay.com>
On Wednesday 04 January 2006 01:43, Eric Dumazet wrote:
> And I would like to pinpoint that set_fd_set() implementation seems *buggy*
> :
>
> It should not use __copy_to_user() but the real one (copy_to_user())
> because the calling thread could have slept in do_select() and another
> thread played mm games during this sleep.
__ only skips the access_ok which checks the kernel/user boundary, and the
kernel/user boundary doesn't change even while sleeping.
On very early 386s it did something more to work around a CPU bug, but that is
racy on multithreaded processes in any case. Not really worth caring about.
Also I doubt any such machines are left in working condition. That old
workaround code could be probably safely removed by now.
-Andi
prev parent reply other threads:[~2006-01-04 0:48 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-03 20:58 [PATCH] [RFC] Optimize select/poll by putting small data sets on the stack Andi Kleen
2006-01-03 22:14 ` Eric Dumazet
2006-01-03 23:05 ` Andi Kleen
2006-01-03 23:07 ` Eric Dumazet
2006-01-03 23:13 ` Andi Kleen
2006-01-03 22:22 ` Jesper Juhl
2006-01-03 23:07 ` Andi Kleen
2006-01-04 0:28 ` Arnd Bergmann
2006-01-04 0:33 ` Andi Kleen
2006-01-04 0:43 ` Eric Dumazet
2006-01-04 0:48 ` Andi Kleen [this message]
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