Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933175AbWLaNjZ (ORCPT ); Sun, 31 Dec 2006 08:39:25 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S933172AbWLaNjY (ORCPT ); Sun, 31 Dec 2006 08:39:24 -0500 Received: from ns.firmix.at ([62.141.48.66]:49345 "EHLO ns.firmix.at" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933175AbWLaNjX (ORCPT ); Sun, 31 Dec 2006 08:39:23 -0500 Subject: Re: [PATCH] [DISCUSS] Make the variable NULL after freeing it. From: Bernd Petrovitsch To: Jan Engelhardt Cc: Pavel Machek , Amit Choudhary , Linux Kernel In-Reply-To: References: <20061221234127.29189.qmail@web55606.mail.re4.yahoo.com> <20061227171010.GA4088@ucw.cz> Content-Type: text/plain Organization: http://www.firmix.at/ Date: Sun, 31 Dec 2006 14:38:32 +0100 Message-Id: <1167572312.3318.47.camel@gimli.at.home> Mime-Version: 1.0 X-Mailer: Evolution 2.8.2.1 (2.8.2.1-2.fc6) Content-Transfer-Encoding: 7bit X-Firmix-Scanned-By: MIMEDefang 2.56 on ns.firmix.at X-Spam-Score: -2.41 () AWL,BAYES_00,FORGED_RCVD_HELO X-Firmix-Spam-Status: No, hits=-2.41 required=5 X-Firmix-Spam-Score: -2.41 () AWL,BAYES_00,FORGED_RCVD_HELO Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1786 Lines: 48 On Thu, 2006-12-28 at 09:54 +0100, Jan Engelhardt wrote: > On Dec 27 2006 17:10, Pavel Machek wrote: > > >> Was just wondering if the _var_ in kfree(_var_) could be set to > >> NULL after its freed. It may solve the problem of accessing some > >> freed memory as the kernel will crash since _var_ was set to NULL. > >> > >> Does this make sense? If yes, then how about renaming kfree to > >> something else and providing a kfree macro that would do the > >> following: > >> > >> #define kfree(x) do { \ > >> new_kfree(x); \ > >> x = NULL; \ > >> } while(0) > >> > >> There might be other better ways too. ---- snip ---- (x) = NULL; \ ---- snip ---- ? > >No, that would be very confusing. Otoh having > >KFREE() do kfree() and assignment might be acceptable. > > What about setting x to some poison value from ? That depends on the decision/definition if (so called) "double free" is an error or not (and "free(NULL)" must work in POSIX-compliant environments). Personally I think it is pointless to disallow "kfree(NULL)" by using some poison value and force people to add a "we have to free that variable" variable to work around it instead of keeping it NULL (which makes the "kfree($variable)" a no-op). Former discussions are to be found in the archives ...... Bernd -- Firmix Software GmbH http://www.firmix.at/ mobil: +43 664 4416156 fax: +43 1 7890849-55 Embedded Linux Development and Services - 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/