From owner-freebsd-hackers Tue Oct 2 6:15:44 2001 Delivered-To: freebsd-hackers@freebsd.org Received: from ringworld.nanolink.com (straylight.ringlet.net [217.75.134.254]) by hub.freebsd.org (Postfix) with SMTP id 3782937B40C for ; Tue, 2 Oct 2001 06:15:34 -0700 (PDT) Received: (qmail 11689 invoked by uid 1000); 2 Oct 2001 13:04:14 -0000 Date: Tue, 2 Oct 2001 16:04:14 +0300 From: Peter Pentchev To: Greg Lehey Cc: Julian Elischer , Gersh , Bernd Walter , Anjali Kulkarni , freebsd-hackers@FreeBSD.ORG Subject: Re: setjmp/longjmp Message-ID: <20011002160414.B10919@ringworld.oblivion.bg> Mail-Followup-To: Greg Lehey , Julian Elischer , Gersh , Bernd Walter , Anjali Kulkarni , freebsd-hackers@FreeBSD.ORG References: <20011001105624.C31215@wantadilla.lemis.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: <20011001105624.C31215@wantadilla.lemis.com>; from grog@FreeBSD.org on Mon, Oct 01, 2001 at 10:56:24AM +0930 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 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'. G'luck, Peter -- Do you think anybody has ever had *precisely this thought* before? To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message