From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Hurley Subject: Re: n_tty_write() going into schedule but NOT coming out Date: Tue, 02 Apr 2013 09:38:42 -0400 Message-ID: <1364909922.3617.41.camel@thor.lan> References: <5156DC21.20901@synopsys.com> <5159925B.5050806@synopsys.com> <1364829008.3617.21.camel@thor.lan> <515ADC96.7090908@synopsys.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: Received: from mailout02.c08.mtsvc.net ([205.186.168.190]:57069 "EHLO mailout02.c08.mtsvc.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761203Ab3DBNi7 (ORCPT ); Tue, 2 Apr 2013 09:38:59 -0400 In-Reply-To: <515ADC96.7090908@synopsys.com> Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: Vineet Gupta Cc: lkml , linux-serial@vger.kernel.org, Ingo Molnar , Peter Zijlstra , Jiri Slaby On Tue, 2013-04-02 at 18:56 +0530, Vineet Gupta wrote: > On 04/01/2013 08:40 PM, Peter Hurley wrote: > > On Mon, 2013-04-01 at 19:27 +0530, Vineet Gupta wrote: > >> On 03/30/2013 06:05 PM, Vineet Gupta wrote: > >>> Hung find task is sitting in the schedule() call in n_tty_write() > >>> > >>> [ARCLinux]$ cat /proc/281/stack > >>> [<8065945e>] n_tty_write+0x23a/0x424 > >>> [<80655cd4>] tty_write+0x1ac/0x2d4 > >>> [<805976ba>] vfs_write+0x92/0x110 > >>> [<80597816>] sys_write+0x4e/0x88 > >>> [<8050e780>] ret_from_system_call+0x0/0x4 > > Likely the writer is stuck because the receive buffer is full and the > > reader is hung. What are the respective shells and telnetd doing? > > I don't undersand how the receive buffer full/empty is coming into play - that > schedule() call is not a wait queue or something If n_tty_write() blocks [the schedule() call], then it is on a wait queue (tty->write_wait) which is woken by pty's unthrottle() called from n_tty_read from the linked pty when space becomes available in the receive buffer.