From owner-freebsd-hackers Wed Oct 3 17:58:25 2001 Delivered-To: freebsd-hackers@freebsd.org Received: from wantadilla.lemis.com (wantadilla.lemis.com [192.109.197.80]) by hub.freebsd.org (Postfix) with ESMTP id 36B0937B401 for ; Wed, 3 Oct 2001 17:58:20 -0700 (PDT) Received: by wantadilla.lemis.com (Postfix, from userid 1004) id 4AB736AB08; Thu, 4 Oct 2001 10:29:13 +0930 (CST) Date: Thu, 4 Oct 2001 10:29:13 +0930 From: Greg Lehey To: Julian Elischer Cc: Anjali Kulkarni , Peter Pentchev , Gersh , Bernd Walter , freebsd-hackers@FreeBSD.ORG Subject: Re: setjmp/longjmp Message-ID: <20011004102913.C69005@wantadilla.lemis.com> References: <009801c14bcf$d63e5fd0$0a00a8c0@indranet> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: ; from julian@elischer.org on Wed, Oct 03, 2001 at 12:12:14PM -0700 Organization: The FreeBSD Project Phone: +61-8-8388-8286 Fax: +61-8-8388-8725 Mobile: +61-418-838-708 WWW-Home-Page: http://www.FreeBSD.org/ X-PGP-Fingerprint: 6B 7B C3 8C 61 CD 54 AF 13 24 52 F8 6D A4 95 EF Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG On Wednesday, 3 October 2001 at 12:12:14 -0700, Julian Elischer wrote: > I suppose it must have been Peter Penchev who wrote: >> On Wednesday, October 03, 2001 6:14 AM, Greg Lehey wrote: >>> On Tuesday, 2 October 2001 at 12:43:54 -0700, Julian Elischer wrote: >>>> On Tue, 2 Oct 2001, Peter Pentchev wrote: >>>>> On Mon, Oct 01, 2001 at 10:56:24AM +0930, Greg Lehey wrote: >>>>>> [Format recovered--see http://www.lemis.com/email/email-format.html] >>>>>> >>>>>> On Friday, 28 September 2001 at 10:12:14 -0700, Julian Elischer wrote: >>>>>>> On Fri, 28 Sep 2001, Gersh wrote: >>>>>>>> On Fri, 28 Sep 2001, Bernd Walter wrote: >>>>>>>>> On Fri, Sep 28, 2001 at 07:03:51PM +0530, Anjali Kulkarni wrote: >>>>>>>>>> Does anyone know whether it is advisable or not to use >>>>>>>>>> setjmp/longjmp within kernel code? I could not see any >>>>>>>>>> setjmp/longjmp in kernel source code. Is there a good reason for >>>>>>>>>> this or can it be used? >>>>>>>>> >>>>>>>>> You need to look again, it's used in several places in the kernel. >>>>>>>> >>>>>>>> Look at sys/i386/i386/db_interface.c >>>>>>> >>>>>>> Yeah but it would probably be a pretty bad idea to use it without >>>>>>> very careful thought. Especialy with the kernel becoming >>>>>>> pre-emptable in the future.. >>>>>> >>>>>> Can you think of a scenario where it wouldn't work? Preemption >>>>>> doesn't tear stacks apart, right? >>>>> >>>>> How about a case of a longjmp() back from under an acquired lock/mutex? >>>>> Like function A sets up a jump buffer, calls function B, B acquires >>>>> a lock, B calls C, C longjmp()'s back to A; what happens to the lock? >>>>> >>>>> It would work if A were aware of B's lock and the possibility of a code >>>>> path that would end up with it still being held; I presume that this is >>>>> what Julian meant by 'very careful thought'. >>>> >>>> pretty much... >>> >>> That's wrong, of course, but I don't see what this has to do with >>> preemptive kernels. This is the same incorrect usages as performing >>> malloc() and then longjmp()ing over the free(). >> >> Right, that was my question too, doesent seem connected with pre-emptive >> kernels... > > basically it's just that pre-emtion just muddies the waters more.. Or statements which aren't backed up with examples? Greg -- See complete headers for address and phone numbers To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message