From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751413AbWG2NR5 (ORCPT ); Sat, 29 Jul 2006 09:17:57 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751434AbWG2NR5 (ORCPT ); Sat, 29 Jul 2006 09:17:57 -0400 Received: from ra.tuxdriver.com ([70.61.120.52]:34570 "EHLO ra.tuxdriver.com") by vger.kernel.org with ESMTP id S1751413AbWG2NR4 (ORCPT ); Sat, 29 Jul 2006 09:17:56 -0400 Date: Sat, 29 Jul 2006 09:14:19 -0400 From: Neil Horman To: kernel-janitors@osdl.org, linux-kernel@vger.kernel.org, schwidefsky@de.ibm.com Subject: Re: [KJ] audit return code handling for kernel_thread [2/11] Message-ID: <20060729131419.GA6892@localhost.localdomain> References: <200607282007.k6SK7DhX009584@ra.tuxdriver.com> <20060729093704.GD26956@flint.arm.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20060729093704.GD26956@flint.arm.linux.org.uk> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jul 29, 2006 at 10:37:04AM +0100, Russell King wrote: > On Fri, Jul 28, 2006 at 04:07:13PM -0400, nhorman@tuxdriver.com wrote: > > Audit/Cleanup of kernel_thread calls, specifically checking of return codes. > > Problems seemed to fall into 3 main categories: > > > > 1) callers of kernel_thread were inconsistent about meaning of a zero return > > code. Some callers considered a zero return code to mean success, others took > > it to mean failure. a zero return code, while not actually possible in the > > current implementation, should be considered a success (pid 0 is/should be > > valid). fixed all callers to treat zero return as success > > > > 2) caller of kernel_thread saved return code of kernel_thread for later use > > without ever checking its value. Callers who did this tended to assume a > > non-zero return was success, and would often wait for a completion queue to be > > woken up, implying that an error (negative return code) from kernel_thread could > > lead to deadlock. Repaired by checking return code at call time, and setting > > saved return code to zero in the event of an error. > > This is inconsistent with your assertion that pid 0 "is/should be valid" > above. If you want '0' to mean "not valid" then it's not a valid return > value from kernel_thread() (and arguably that's true, since pid 0 is > permanently allocated to the idle thread.) > No its, not, but I can see how my comments might be ambiguous. I want zero to be a valid return code, since we never actually return zero, but we certainly could if we wanted to. Note that kernel_thread returns an int (not an unsigned int), and as such assuming that a non-zero return code implies success ignores the fact that kernel_thread can return a negative value, which indicates failure. This is what I found, and what my patch fixes. > I don't particularly care whether you decide to that returning pid 0 from > kernel_thread is valid or not, just that your two points above are at least > consistent with each other. > My comments in (2) should be made more clear by changing "assume a non-zero return was success" to "assume a negative return was success". This is what my patch fixes. Thanks & Regards Neil > -- > Russell King > Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ > maintainer of: 2.6 Serial core