From: David Miller <davem@davemloft.net>
To: adobriyan@gmail.com
Cc: eric.dumazet@gmail.com, shemminger@linux-foundation.org,
netdev@vger.kernel.org, bhutchings@solarflare.com
Subject: Re: [PATCH v2] tcp: restrict net.ipv4.tcp_adv_win_scale (#20312)
Date: Sun, 28 Nov 2010 10:39:20 -0800 (PST) [thread overview]
Message-ID: <20101128.103920.226762370.davem@davemloft.net> (raw)
In-Reply-To: <20101122225421.GA7372@core2.telecom.by>
From: Alexey Dobriyan <adobriyan@gmail.com>
Date: Tue, 23 Nov 2010 00:54:21 +0200
> tcp_win_from_space() does the following:
>
> if (sysctl_tcp_adv_win_scale <= 0)
> return space >> (-sysctl_tcp_adv_win_scale);
> else
> return space - (space >> sysctl_tcp_adv_win_scale);
>
> "space" is int.
>
> As per C99 6.5.7 (3) shifting int for 32 or more bits is
> undefined behaviour.
>
> Indeed, if sysctl_tcp_adv_win_scale is exactly 32,
> space >> 32 equals space and function returns 0.
>
> Which means we busyloop in tcp_fixup_rcvbuf().
>
> Restrict net.ipv4.tcp_adv_win_scale to [-31, 31].
>
> Fix https://bugzilla.kernel.org/show_bug.cgi?id=20312
>
> Steps to reproduce:
>
> echo 32 >/proc/sys/net/ipv4/tcp_adv_win_scale
> wget www.kernel.org
> [softlockup]
>
> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
I'll aply this, thanks Alexey.
prev parent reply other threads:[~2010-11-28 18:38 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-14 15:18 [PATCH] tcp: restrict net.ipv4.tcp_adv_min_scale (#20312) Alexey Dobriyan
2010-11-14 19:49 ` Eric Dumazet
2010-11-14 20:14 ` Alexey Dobriyan
2010-11-15 14:18 ` Ben Hutchings
2010-11-22 22:54 ` [PATCH v2] tcp: restrict net.ipv4.tcp_adv_win_scale (#20312) Alexey Dobriyan
2010-11-28 18:39 ` David Miller [this message]
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