Date: Wed, 3 Oct 2001 10:14:39 +0930 From: Greg Lehey <grog@FreeBSD.org> To: Julian Elischer <julian@elischer.org> Cc: Peter Pentchev <roam@ringlet.net>, Gersh <gersh@sonn.com>, Bernd Walter <ticso@mail.cicely.de>, Anjali Kulkarni <anjali@indranetworks.com>, freebsd-hackers@FreeBSD.ORG Subject: Re: setjmp/longjmp Message-ID: <20011003101439.K53406@wantadilla.lemis.com> In-Reply-To: <Pine.BSF.4.21.0110021243350.92100-100000@InterJet.elischer.org>; from julian@elischer.org on Tue, Oct 02, 2001 at 12:43:54PM -0700 References: <20011002160414.B10919@ringworld.oblivion.bg> <Pine.BSF.4.21.0110021243350.92100-100000@InterJet.elischer.org>
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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(). 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
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