From owner-cvs-all@FreeBSD.ORG Thu Mar 3 20:27:17 2005 Return-Path: Delivered-To: cvs-all@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id F3E4016A4CE; Thu, 3 Mar 2005 20:27:16 +0000 (GMT) Received: from mail.vicor-nb.com (bigwoop.vicor-nb.com [208.206.78.2]) by mx1.FreeBSD.org (Postfix) with ESMTP id C343E43D2F; Thu, 3 Mar 2005 20:27:16 +0000 (GMT) (envelope-from julian@elischer.org) Received: from [208.206.78.97] (julian.vicor-nb.com [208.206.78.97]) by mail.vicor-nb.com (Postfix) with ESMTP id 79D3E7A41E; Thu, 3 Mar 2005 12:27:16 -0800 (PST) Message-ID: <42277324.3060102@elischer.org> Date: Thu, 03 Mar 2005 12:27:16 -0800 From: Julian Elischer User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.7.5) Gecko/20050218 X-Accept-Language: en, hu MIME-Version: 1.0 To: David Xu References: <200503021343.j22DhpQ3075008@repoman.freebsd.org> <200503020915.28512.jhb@FreeBSD.org> <4226446B.7020406@freebsd.org> <20050303033115.GA13174@VARK.MIT.EDU> <42269DB0.6070107@freebsd.org> <20050303052902.GA14011@VARK.MIT.EDU> <4226A46B.2090704@freebsd.org> In-Reply-To: <4226A46B.2090704@freebsd.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit cc: cvs-src@FreeBSD.org cc: David Schultz cc: src-committers@FreeBSD.org cc: cvs-all@FreeBSD.org cc: John Baldwin Subject: Re: cvs commit: src/sys/kern kern_sig.c X-BeenThere: cvs-all@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: CVS commit messages for the entire tree List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 03 Mar 2005 20:27:17 -0000 David Xu wrote: > David Schultz wrote: > >> You have to worry about that anyway, though. A and B need to know >> that they're not allowed to hold locks across the calls if C calls >> msleep(), for instance. Anyway, your proposal if having a flag >> for msleep() is basically the same as my proposal of having a >> separate function. (The only difference is that adding a separate >> function doesn't break the ABI.) So it sounds like we're more or >> less in agreement here. >> >> >> > This is not a lock problem, this is the problem why a stack variable > can not > be used when thread is going to sleep, this is a rather odd behavior > to me. > For example, thread A stack variable address p is put on a known place, > e.g, a queue, thread A unlocks the lock of the queue and sleeps, > sometimes later, a producer thread B writes the data into memory > pointed by p, > and wake up A, that's a very simple code, here malloc is not needed at > all. > At the time, kernel shoudn't swap out the thread stack, any code > trying to swap > it out is totally broken. this is why it is common kernel lore to not use the stack for anything that is going to be visible outside the originating function. I guess the clause to be added to the lore is that it shouldn't be used if you are calling down to a function that might make it externally visible as well. > >>>> The alternative, of course, is to just fix the code that assumes >>>> that swapping doesn't exist. >>>> >>>> >>> >>> First find all code written in such way, but it is not that easy. >>> >> >> >> True. If we changed msleep() to disable swapping by default, then >> we wouldn't have to worry about correctness problems related to >> missing some. >> >> >> >>