From owner-freebsd-current@FreeBSD.ORG Fri May 4 22:31:54 2007 Return-Path: X-Original-To: freebsd-current@freebsd.org Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 9CECF16A402 for ; Fri, 4 May 2007 22:31:54 +0000 (UTC) (envelope-from julian@elischer.org) Received: from outC.internet-mail-service.net (outC.internet-mail-service.net [216.240.47.226]) by mx1.freebsd.org (Postfix) with ESMTP id 835E313C46C for ; Fri, 4 May 2007 22:31:54 +0000 (UTC) (envelope-from julian@elischer.org) Received: from idiom.com (mx0.idiom.com [216.240.32.160]) by out.internet-mail-service.net (Postfix) with ESMTP id 7D2D515C26; Fri, 4 May 2007 14:57:59 -0700 (PDT) Received: from julian-mac.elischer.org (nat.ironport.com [63.251.108.100]) by idiom.com (Postfix) with ESMTP id C42C1125ADA; Fri, 4 May 2007 15:31:53 -0700 (PDT) Message-ID: <463BB458.6030606@elischer.org> Date: Fri, 04 May 2007 15:31:52 -0700 From: Julian Elischer User-Agent: Thunderbird 2.0.0.0 (Macintosh/20070326) MIME-Version: 1.0 To: Scott Long References: <463B7A1D.6020602@omnisec.de> <463BF1A7.1050504@FreeBSD.org> <200705041546.50690.jhb@freebsd.org> <463BA850.8000804@elischer.org> <463BAC46.9030200@samsco.org> In-Reply-To: <463BAC46.9030200@samsco.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: attilio@freebsd.org, freebsd-current@freebsd.org, Harald Schmalzbauer Subject: Re: PANIC: blockable slep lock (sx) msi @ ....msi.c:374 X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 04 May 2007 22:31:54 -0000 Scott Long wrote: > Julian Elischer wrote: >> John Baldwin wrote: >> >>> >>> This is wrong because once you do critical_enter(), you are free to >>> assume that you won't do a context switch until you critical_exit(), >>> and sx_xlock() would violate that if it blocked on the lock. >> >> wellllll critical enter doesn't block interupts so it's true if you >> don't call >> an interrupt as a context switch. >> (it doesn't SWITCH contexts but it does step into a different context.) >> > > Yes, interrupts are serviced when a critical section is entered, but > ithreads are not run on the same CPU until the critical section is > exited. This has been debated quite a bit over the last few years, but > I it's a good compromise. This implications just don't seem to be > documented well, especially for those who need a protected, > uninterruptable context for doing time-critical operations. I think what needs to be documented is a list of "Things thou shalt not do whilst within a FAST interrupt handler". possibly in locking/9 amongst other places. maybe in an interrupts(9) page? > > Scott