Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756040AbZAMLg0 (ORCPT ); Tue, 13 Jan 2009 06:36:26 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752345AbZAMLgR (ORCPT ); Tue, 13 Jan 2009 06:36:17 -0500 Received: from mtagate7.de.ibm.com ([195.212.29.156]:47902 "EHLO mtagate7.de.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752049AbZAMLgQ (ORCPT ); Tue, 13 Jan 2009 06:36:16 -0500 Date: Tue, 13 Jan 2009 12:35:45 +0100 From: Hendrik Brueckner Cc: Milton Miller , Benjiman Herrenschmidt , linuxppc-dev list , lkml , Joe Peterson , Alan Cox Subject: Re: [PATCH 1/4] hvc_console: do not set low_latency Message-ID: <20090113113545.GB26819@cetus.boeblingen.de.ibm.com> References: <200901131004.22609.borntraeger@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200901131004.22609.borntraeger@de.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) To: unlisted-recipients:; (no To-header on input) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3990 Lines: 88 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. 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/