linux-kernel - Re: possible regression with pty.c commit

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Date:	Wed, 15 Jul 2009 00:57:13 +0200
From:	Pierre Willenbrock <pierre@...soft.de>
To:	Sergey Senozhatsky <sergey.senozhatsky@...l.by>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: possible regression with pty.c commit

Sergey Senozhatsky schrieb:
> Hello Alan,
> I'm having another problem which I guess may be caused by pty/tty changes.
> The problem is that ppp connection constantly hangups under load (downloading) 
> (it works perfectly with 30 kernel).
> 
> syslog:
> pptp[1942]: anon log[logecho:pptp_ctrl.c:677]: Echo Reply received.
> pptp[1942]: anon log[logecho:pptp_ctrl.c:677]: Echo Reply received.
> pptp[1942]: anon log[logecho:pptp_ctrl.c:677]: Echo Reply received.
> pptp[1942]: anon log[logecho:pptp_ctrl.c:677]: Echo Reply received.
> pptp[1942]: anon log[logecho:pptp_ctrl.c:677]: Echo Reply received.
> pptp[1942]: anon log[logecho:pptp_ctrl.c:677]: Echo Reply received.
> pptp[1942]: anon log[logecho:pptp_ctrl.c:677]: Echo Reply received.
> pptp[1942]: anon log[logecho:pptp_ctrl.c:677]: Echo Request received.
> pptp[1942]: anon log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 6 'Echo-Reply' 
> pppd[1929]: No response to 4 echo-requests
> pppd[1929]: Serial link appears to be disconnected.
> pppd[1929]: Connect time 8.5 minutes.
> 
> In average it works ~10 minutes. 
> I did "strace -ff -F -tt -s 200 -o ... pon ..." which produced 11MiB and 46 files (it'll take some time to dig).
> Do you have any ability to test ppp under load?
> 
> 	Sergey

Hello everyone,

I can reproduce this in mere seconds, using an otherwise idle ppp link
and ping -f -s256 -l256.
Usually, the first batch of packets hangs the pty, but if the link is
not entirely idle, the ping may work for a few more seconds. In fact,
bisect points to commit d945cb9cce20ac7143c2de8d88b187f62db99bdc ("pty:
Rework the pty layer to use the normal buffering logic").

Regards,
  Pierre
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