From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mtagate4.uk.ibm.com (mtagate4.uk.ibm.com [195.212.29.137]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "mtagate4.uk.ibm.com", Issuer "Equifax" (verified OK)) by ozlabs.org (Postfix) with ESMTPS id 6F57DDE2C3 for ; Thu, 15 Jan 2009 20:15:53 +1100 (EST) Received: from d06nrmr1407.portsmouth.uk.ibm.com (d06nrmr1407.portsmouth.uk.ibm.com [9.149.38.185]) by mtagate4.uk.ibm.com (8.13.8/8.13.8) with ESMTP id n0F9Flq7048158 for ; Thu, 15 Jan 2009 09:15:47 GMT Received: from d06av01.portsmouth.uk.ibm.com (d06av01.portsmouth.uk.ibm.com [9.149.37.212]) by d06nrmr1407.portsmouth.uk.ibm.com (8.13.8/8.13.8/NCO v9.1) with ESMTP id n0F9Fkam2363494 for ; Thu, 15 Jan 2009 09:15:46 GMT Received: from d06av01.portsmouth.uk.ibm.com (loopback [127.0.0.1]) by d06av01.portsmouth.uk.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id n0F9FjNs010678 for ; Thu, 15 Jan 2009 09:15:46 GMT Date: Thu, 15 Jan 2009 10:15:44 +0100 From: Hendrik Brueckner To: Benjamin Herrenschmidt Subject: Re: [PATCH 1/4 v2] hvc_console: remove tty->low_latency Message-ID: <20090115091544.GC895@cetus.boeblingen.de.ibm.com> References: <200901131004.22609.borntraeger@de.ibm.com> <20090113113545.GB26819@cetus.boeblingen.de.ibm.com> <1998eda55e236b70f63c7fb4b956b487@bga.com> <1231880644.22571.47.camel@pasglop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1231880644.22571.47.camel@pasglop> Cc: linuxppc-dev list , lkml , Milton Miller , Christian Borntraeger , Hendrik Brueckner , Joe Peterson , Alan Cox List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, Jan 14, 2009 at 08:04:04AM +1100, Benjamin Herrenschmidt wrote: > > So the simplest is to never set it. > > I already applied your previous patch. Please send an incremental fix. Here is the incremental patch for your powerpc tree along with a summary as patch description. Regards, Hendrik -- This patch removes the tty->low_latency setting. For irq based hvc_console backends the tty->low_latency must be set to 0, because the tty_flip_buffer_push() function must not be called from IRQ context (see drivers/char/tty_buffer.c). For polled backends, the low_latency setting causes the bug trace below, because tty_flip_buffer_push() is called within an atomic context and subsequent calls might sleep due to mutex_lock. 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 Signed-off-by: Hendrik Brueckner --- drivers/char/hvc_console.c | 2 -- 1 file changed, 2 deletions(-) --- a/drivers/char/hvc_console.c +++ b/drivers/char/hvc_console.c @@ -318,8 +318,6 @@ static int hvc_open(struct tty_struct *t } /* else count == 0 */ tty->driver_data = hp; - if (!hp->irq_requested) - tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */ hp->tty = tty;