From owner-svn-src-projects@FreeBSD.ORG Mon Jul 30 20:48:11 2012 Return-Path: Delivered-To: svn-src-projects@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id E1167106566B; Mon, 30 Jul 2012 20:48:10 +0000 (UTC) (envelope-from asmrookie@gmail.com) Received: from mail-lpp01m010-f54.google.com (mail-lpp01m010-f54.google.com [209.85.215.54]) by mx1.freebsd.org (Postfix) with ESMTP id F18EA8FC14; Mon, 30 Jul 2012 20:48:09 +0000 (UTC) Received: by laai10 with SMTP id i10so4399797laa.13 for ; Mon, 30 Jul 2012 13:48:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:reply-to:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type; bh=BCZzjHwNojFecN7dqV1rwkcDyyePEuqQRc4cW2ST5RY=; b=o9dVAlpzMGy4NHpAt7m8a++cBfT1igEgo/F72X+4XWs+Vi/gd1Io5ToUUeGyDUM4ja trEfju8fHdxSmqR4pmvpZVJ2PrMozaOLn39Ok+nI2r54tEqEU7cXsmE4Qw4a4/AHtMZZ NVEmesvQaP2Uz6kW8Oe7jui/+6soQgoJjGDQ1dMFtZblhZKopmGkJNO9MpHzfJV1tms/ KYcP2TOCSlTqinGilsTrzqtc/fyMPKdxm3c8vGUMGz6MMtl5STSsmkMqCLnSK8ZOGcZY /5W4v+6sekk0OOJtUqQvSwKNQ/Kv4TVjT25pFFTHKbgxJ6r2hhFz9051sb1i6QkwW3tt 3kyw== MIME-Version: 1.0 Received: by 10.112.103.194 with SMTP id fy2mr5793001lbb.64.1343681288746; Mon, 30 Jul 2012 13:48:08 -0700 (PDT) Sender: asmrookie@gmail.com Received: by 10.112.27.65 with HTTP; Mon, 30 Jul 2012 13:48:08 -0700 (PDT) In-Reply-To: <20120730145912.GZ2676@deviant.kiev.zoral.com.ua> References: <201207301350.q6UDobCI099069@svn.freebsd.org> <20120730143943.GY2676@deviant.kiev.zoral.com.ua> <20120730145912.GZ2676@deviant.kiev.zoral.com.ua> Date: Mon, 30 Jul 2012 21:48:08 +0100 X-Google-Sender-Auth: Gd3_xgmEJSDIek0VKr5_XOFcEYs Message-ID: From: Attilio Rao To: Konstantin Belousov Content-Type: text/plain; charset=UTF-8 Cc: Davide Italiano , svn-src-projects@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r238907 - projects/calloutng/sys/kern X-BeenThere: svn-src-projects@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: attilio@FreeBSD.org List-Id: "SVN commit messages for the src " projects" tree" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 30 Jul 2012 20:48:11 -0000 On Mon, Jul 30, 2012 at 3:59 PM, Konstantin Belousov wrote: > On Mon, Jul 30, 2012 at 03:51:22PM +0100, Attilio Rao wrote: >> On 7/30/12, Konstantin Belousov wrote: >> > On Mon, Jul 30, 2012 at 03:24:26PM +0100, Attilio Rao wrote: >> >> On 7/30/12, Davide Italiano wrote: >> >> > On Mon, Jul 30, 2012 at 4:02 PM, Attilio Rao >> >> > wrote: >> >> > Thanks for the comment, Attilio. >> >> > Yes, it's exactly what you thought. If direct flag is equal to one >> >> > you're sure you're processing a callout which runs directly from >> >> > hardware interrupt context. In this case, the running thread cannot >> >> > sleep and it's likely you have TDP_NOSLEEPING flags set, failing the >> >> > KASSERT() in THREAD_NO_SLEEPING() and leading to panic if kernel is >> >> > compiled with INVARIANTS. >> >> > In case you're running from SWI context (direct equals to zero) code >> >> > remains the same as before. >> >> > I think what I'm doing works due the assumption thread running never >> >> > sleeps. Do you suggest some other way to handle this? >> >> >> >> Possibly the quicker way to do this is to have a way to deal with the >> >> TDP_NOSLEEPING flag in recursed way, thus implement the same logic as >> >> VFS_LOCK_GIANT() does, for example. >> >> You will need to change the few callers of THREAD_NO_SLEEPING(), but >> >> the patch should be no longer than 10/15 lines. >> > >> > There are already curthread_pflags_set/restore KPI designed exactly to >> > handle >> > nested private thread flags. >> >> Yes, however I would use curthread_pflags* KPI within >> THREAD_NO_SLEEPING() as this name is much more explicit. >> > Sure, hiding it in THREAD_NO_SLEEPING (THREAD_NO_SLEEP_ENTER/LEAVE ?) > is the way to use curthread_pflags_set there. > > As a second though, on the other hand, is it safe to modify td_flags > from the interrupt context at all ? Probably yes if interrupt handler > always leave td_pflags in the same state on leave as it was on entry, > but couldn't too smart compiler cause inconsistent view of td_pflags > inside the handler ? Can you think of any? Because I cannot think of a case where a nested interrupt can messup with already compiled code, unless it leaks a cleanup. I was more worried about the compiler reordering operations before locking could really see it, but I think in this case the functions call to sleepqueue (at least) works as a sequence point so we are safe. > >> > Also, I wonder, should you assert somehow that direct dispatch cannot block >> > as well ? >> >> Yes, it would be optimal, but I don't think we have a flag for that >> right now, do we? > > I am not aware of such flag, this might be a good reason to introduce it, > if issue about td_pflags is just a product of my imagination. I think you should be good to go. Do you plan to work on such a patch? Thanks, Attilio -- Peace can only be achieved by understanding - A. Einstein