Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755597AbZAMP45 (ORCPT ); Tue, 13 Jan 2009 10:56:57 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752710AbZAMP4p (ORCPT ); Tue, 13 Jan 2009 10:56:45 -0500 Received: from mercury.realtime.net ([205.238.132.86]:45821 "EHLO mercury.realtime.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752788AbZAMP4o (ORCPT ); Tue, 13 Jan 2009 10:56:44 -0500 In-Reply-To: <20090113113545.GB26819@cetus.boeblingen.de.ibm.com> References: <200901131004.22609.borntraeger@de.ibm.com> <20090113113545.GB26819@cetus.boeblingen.de.ibm.com> Mime-Version: 1.0 (Apple Message framework v624) Content-Type: text/plain; charset=US-ASCII; format=flowed Message-Id: <1998eda55e236b70f63c7fb4b956b487@bga.com> Content-Transfer-Encoding: 7bit Cc: Alan Cox , Benjiman Herrenschmidt , linuxppc-dev list , Joe Peterson , lkml From: Milton Miller Subject: Re: [PATCH 1/4] hvc_console: do not set low_latency Date: Tue, 13 Jan 2009 10:03:54 -0600 To: Hendrik Brueckner X-Mailer: Apple Mail (2.624) X-Originating-IP: 205.232.218.100 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4261 Lines: 114 On Jan 13, 2009, at 5:35 AM, Hendrik Brueckner wrote: > Here is yet another bug trace related to the low_latency issue, that is > experienced using the hvc_iucv backend. The hvc_iucv backend now also > uses irq > notifiers. > The bug trace below appears if hvc_kick() is called. > > On Tue, Jan 13, 2009 at 10:04:22AM +0100, Christian Borntraeger wrote: >> Am Donnerstag 08 Januar 2009 schrieb Milton Miller: >>> hvc_console is setting low_latency unconditionally, but some clients >>> are >>> interrupt driven and will call hvc_poll from irq context. This will >>> cause >>> tty_flip_buffer_push to be called from irq context, and it very >>> clearly >>> states it must not be called from IRQ when low_latency is specified. > It seems that if low_latency is set, tty_flip_buffer_push() should > also not be > called within an atomic context, because echo_char_raw() and other > echo* calls > might sleep. > > Christian's patch solves this problem for irq driven backends. > However, there might be still a problem with polled backends since the > khvcd() > thread calls hvc_poll() while hvc_structs_lock is held. > > I think the hvc_udbg backend is based on polling. > David, could you check if you experience any problems with your > hvc_udbg > backend on latest git. > So the simplest is to never set it. milton > BUG: sleeping function called from invalid context at > /root/cvs/linux-2.6.git/kernel/mutex.c:207 > in_atomic(): 1, irqs_disabled(): 0, pid: 748, name: khvcd > 1 lock held by khvcd/748: > #0: (hvc_structs_lock){--..}, at: [<00000000002ceb50>] > khvcd+0x58/0x12c > CPU: 0 Not tainted 2.6.29-rc1git #29 > Process khvcd (pid: 748, task: 000000002fb9a480, ksp: 000000002f66bd78) > 070000000000000a 000000002f66ba00 0000000000000002 (null) > 000000002f66baa0 000000002f66ba18 000000002f66ba18 > 0000000000104f08 > ffffffffffffc000 000000002f66bd78 (null) (null) > 000000002f66ba00 000000000000000c 000000002f66ba00 > 000000002f66ba70 > 0000000000466af8 0000000000104f08 000000002f66ba00 > 000000002f66ba50 > Call Trace: > ([<0000000000104e7c>] show_trace+0x138/0x158) > [<0000000000104f62>] show_stack+0xc6/0xf8 > [<0000000000105740>] dump_stack+0xb0/0xc0 > [<000000000013144a>] __might_sleep+0x14e/0x17c > [<000000000045e226>] mutex_lock_nested+0x42/0x3b4 > [<00000000002c443e>] echo_char_raw+0x3a/0x9c > [<00000000002c688c>] n_tty_receive_buf+0x1154/0x1208 > [<00000000002ca0a2>] flush_to_ldisc+0x152/0x220 > [<00000000002ca1da>] tty_flip_buffer_push+0x6a/0x90 > [<00000000002cea74>] hvc_poll+0x244/0x2c8 > [<00000000002ceb68>] khvcd+0x70/0x12c > [<000000000015bbd0>] kthread+0x68/0xa0 > [<0000000000109d5a>] kernel_thread_starter+0x6/0xc > [<0000000000109d54>] kernel_thread_starter+0x0/0xc > 1 lock held by khvcd/748: > #0: (hvc_structs_lock){--..}, at: [<00000000002ceb50>] > khvcd+0x58/0x12c > >> This wont work, since the call to notifier_add is done later: >> What about: >> --- >> drivers/char/hvc_console.c | 5 +++-- >> 1 file changed, 3 insertions(+), 2 deletions(-) >> >> Index: linux-2.6/drivers/char/hvc_console.c >> =================================================================== >> --- linux-2.6.orig/drivers/char/hvc_console.c >> +++ linux-2.6/drivers/char/hvc_console.c >> @@ -318,8 +318,6 @@ static int hvc_open(struct tty_struct *t >> } /* else count == 0 */ >> >> tty->driver_data = hp; >> - tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */ >> - >> hp->tty = tty; >> >> spin_unlock_irqrestore(&hp->lock, flags); >> @@ -327,6 +325,9 @@ static int hvc_open(struct tty_struct *t >> if (hp->ops->notifier_add) >> rc = hp->ops->notifier_add(hp, hp->data); >> >> + if (!hp->irq_requested) >> + tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */ >> + >> /* >> * If the notifier fails we return an error. The tty layer >> * will call hvc_close() after a failed open but we don't want to >> clean > > Acked-by: Hendrik Brueckner > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/