From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262052AbVGOUcK (ORCPT ); Fri, 15 Jul 2005 16:32:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262080AbVGOUcK (ORCPT ); Fri, 15 Jul 2005 16:32:10 -0400 Received: from caramon.arm.linux.org.uk ([212.18.232.186]:34060 "EHLO caramon.arm.linux.org.uk") by vger.kernel.org with ESMTP id S262052AbVGOUcG (ORCPT ); Fri, 15 Jul 2005 16:32:06 -0400 Date: Fri, 15 Jul 2005 21:32:01 +0100 From: Russell King To: karl malbrain Cc: "Linux-Kernel@Vger. Kernel. Org" Subject: Re: 2.6.9: serial_core: uart_open Message-ID: <20050715213201.C23709@flint.arm.linux.org.uk> Mail-Followup-To: karl malbrain , "Linux-Kernel@Vger. Kernel. Org" References: <20050715082859.B23102@flint.arm.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5.1i In-Reply-To: ; from karl@petzent.com on Fri, Jul 15, 2005 at 09:02:48AM -0700 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 15, 2005 at 09:02:48AM -0700, karl malbrain wrote: > > -----Original Message----- > > From: Russell King > > Sent: Friday, July 15, 2005 12:29 AM > > To: karl malbrain > > Cc: Linux-Kernel@Vger. Kernel. Org > > Subject: Re: 2.6.9: serial_core: uart_open > > > > > > On Thu, Jul 14, 2005 at 03:35:07PM -0700, karl malbrain wrote: > > > AT LAST I HAVE SOME DATA!!! > > > > > > The problem is that ALL SYSTEM CALLS to open "/dev/tty" are > > blocking!! even > > > with O_NDELAY set and even from completely disjoint sessions. > > I discovered > > > this via issuing "strace sh". That's why the new xterm windows froze. > > > > > > The original process doing the open("/dev/ttyS1", O_RDWR) is > > listed in the > > > ps aux listing as status S+. > > > > Ok, 'S' means it's sleeping. > > > > Can you enable Magic SYSRQ, and ensure that you have a large kernel > > log buffer (the LOG_BUF_SHIFT configuration symbol). Ensure that > > /proc/sys/kernel/sysrq is 1, and re-run your test such that you have > > something else waiting (eg, the strace sh). Then hit Alt-SysRQ-T. > > > > You can then read the kernel messages with dmesg - you may need the > > -s argument to capture the entire kernel buffer. > > > > This will tell us where all processes are sleeping. > > > sh D 00000006 3036 5341 5252 (NOTLB) > d0408eb0 00000086 c01c14d7 00000006 d0408e94 000f4fa5 c0d38f81 000039a0 > df461240 df4613cc c035ff00 00000246 d0408ecc df461240 c0300e33 > 00000001 > df461240 c011c856 c035ff20 c035ff20 d0408000 00000001 c035abe0 > d0408000 > Call Trace: > [] inode_has_perm+0x4c/0x54 > [] __down+0x103/0x1fe > [] default_wake_function+0x0/0xc > [] __down_failed+0x8/0xc > [] .text.lock.tty_io+0x87/0x10f > [] chrdev_open+0x325/0x3b9 This seems to imply that there's a lock being taken in tty_open(). The 2.6.9 source contains no such thing. Are you sure you're using an unpatched 2.6.9 kernel? > [] dentry_open+0xbd/0x180 > [] filp_open+0x36/0x3c > [] direct_strncpy_from_user+0x46/0x5d > [] sys_open+0x31/0x7d > [] syscall_call+0x7/0xb -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: 2.6 Serial core