From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263360AbVGOUwY (ORCPT ); Fri, 15 Jul 2005 16:52:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263367AbVGOUwY (ORCPT ); Fri, 15 Jul 2005 16:52:24 -0400 Received: from taxbrain.com ([64.162.14.3]:32857 "EHLO petzent.com") by vger.kernel.org with ESMTP id S263360AbVGOUwW (ORCPT ); Fri, 15 Jul 2005 16:52:22 -0400 From: "karl malbrain" To: "Russell King" Cc: "Linux-Kernel@Vger. Kernel. Org" Subject: RE: 2.6.9 chrdev_open: serial_core: uart_open Date: Fri, 15 Jul 2005 13:52:15 -0700 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook IMO, Build 9.0.6604 (9.0.2911.0) X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1441 Importance: Normal In-Reply-To: <20050715213058.B23709@flint.arm.linux.org.uk> X-Spam-Processed: petzent.com, Fri, 15 Jul 2005 13:48:29 -0700 (not processed: message from valid local sender) X-Return-Path: karl@petzent.com X-MDaemon-Deliver-To: linux-kernel@vger.kernel.org X-MDAV-Processed: petzent.com, Fri, 15 Jul 2005 13:48:32 -0700 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > -----Original Message----- > From: Russell King > Sent: Friday, July 15, 2005 1:31 PM > To: karl malbrain > Cc: Linux-Kernel@Vger. Kernel. Org > Subject: Re: 2.6.9 chrdev_open: serial_core: uart_open > > > On Fri, Jul 15, 2005 at 01:11:33PM -0700, karl malbrain wrote: > > > -----Original Message----- > > > From: Russell King > > > Sent: Friday, July 15, 2005 12:23 AM > > > To: karl malbrain > > > Cc: Linux-Kernel@Vger. Kernel. Org > > > Subject: Re: 2.6.9 chrdev_open: serial_core: uart_open > > > > > > > > > On Thu, Jul 14, 2005 at 04:50:00PM -0700, karl malbrain wrote: > > > > chrdev_open issues a lock_kernel() before calling uart_open. > > > > > > > > It would appear that servicing the blocking open request > > > uart_open goes to > > > > sleep with the kernel locked. Would this shut down > subsequent access to > > > > opening "/dev/tty"??? > > > > > > No. lock_kernel() is automatically released when a process sleeps. > > > > Drilling down between the uart_open and chrdev_open into tty_open is a > > semaphore tty_sem that is being held during the sleep cycle in > uart_open. > > chrdev_open() calls tty_open(), which then calls init_dev(). init_dev() > takes tty_sem, does its stuff, and then releases tty_sem. A little > later on, tty_open() calls the uart driver's uart_open() function. > > So it does this with tty_sem unlocked. On my 2.6.9-11EL source it clearly shows the up(&tty_sem) after the call to uart_open. Init_dev never touches tty_sem. karl m