From owner-freebsd-current@FreeBSD.ORG Fri Nov 12 20:24:49 2010 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id AC60C10656C9; Fri, 12 Nov 2010 20:24:49 +0000 (UTC) (envelope-from hselasky@c2i.net) Received: from swip.net (mailfe01.swip.net [212.247.154.1]) by mx1.freebsd.org (Postfix) with ESMTP id 0892A8FC08; Fri, 12 Nov 2010 20:24:48 +0000 (UTC) X-Cloudmark-Score: 0.000000 [] X-Cloudmark-Analysis: v=1.1 cv=omSrwDgyMf70S47Fr5SNr0rQzcmIOo0IafWlB/wSLLo= c=1 sm=1 a=WrOSKJTHxIAA:10 a=8nJEP1OIZ-IA:10 a=CL8lFSKtTFcA:10 a=i9M/sDlu2rpZ9XS819oYzg==:17 a=6I5d2MoRAAAA:8 a=8kQB0OdkAAAA:8 a=gAC1W530OKRNHEib3a0A:9 a=k-Ta0indbs3rS3vNmGxkMflgXVgA:4 a=wPNLvfGTeEIA:10 a=SV7veod9ZcQA:10 a=9aOQ2cSd83gA:10 a=i9M/sDlu2rpZ9XS819oYzg==:117 Received: from [188.126.198.129] (account mc467741@c2i.net HELO laptop002.hselasky.homeunix.org) by mailfe01.swip.net (CommuniGate Pro SMTP 5.2.19) with ESMTPA id 49134547; Fri, 12 Nov 2010 21:24:46 +0100 From: Hans Petter Selasky To: freebsd-current@freebsd.org Date: Fri, 12 Nov 2010 21:25:47 +0100 User-Agent: KMail/1.13.5 (FreeBSD/8.1-STABLE; KDE/4.4.5; amd64; ; ) References: <06D5F9F6F655AD4C92E28B662F7F853E039E389A@seaxch09.desktop.isilon.com> <201011121523.18044.hselasky@c2i.net> In-Reply-To: X-Face: +~\`s("[*|O,="7?X@L.elg*F"OA\I/3%^p8g?ab%RN'( =?iso-8859-1?q?=3B=5FIjlA=3A=0A=09hGE=2E=2EEw?=, =?iso-8859-1?q?XAQ*o=23=5C/M=7ESC=3DS1-f9=7BEzRfT=27=7CHhll5Q=5Dha5Bt-s=7Co?= =?iso-8859-1?q?TlKMusi=3A1e=5BwJl=7Dkd=7DGR=0A=09Z0adGx-x=5F0zGbZj=27e?=(Y[(UNle~)8CQWXW@:DX+9)_YlB[tIccCPN$7/L' MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201011122125.47922.hselasky@c2i.net> Cc: mdf@freebsd.org Subject: Re: sleep bug in taskqueue(9) 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, 12 Nov 2010 20:24:49 -0000 On Friday 12 November 2010 17:38:38 mdf@freebsd.org wrote: > On Fri, Nov 12, 2010 at 6:23 AM, Hans Petter Selasky wrote: > > On Friday 12 November 2010 15:18:46 mdf@freebsd.org wrote: > >> On Fri, Nov 12, 2010 at 12:56 AM, Hans Petter Selasky > > > > wrote: > >> > On Thursday 29 April 2010 01:59:58 Matthew Fleming wrote: > >> >> It looks to me like taskqueue_drain(taskqueue_thread, foo) will not > >> >> correctly detect whether or not a task is currently running. The > >> >> check is against a field in the taskqueue struct, but for the > >> >> taskqueue_thread queue with more than one thread, multiple threads > >> >> can simultaneously be running a task, thus stomping over the > >> >> tq_running field. > >> >> > >> >> I have not seen any problem with the code as-is in actual use, so > >> >> this is purely an inspection bug. > >> >> > >> >> The following patch should fix the problem. Because it changes the > >> >> size of struct task I'm not sure if it would be suitable for MFC. > >> > > >> > 1) The u_char is going to leave a hole in that structure on ARM > >> > platforms for example. > >> > > >> > 2) The existing taskqueue implementation also has a missing check for > >> > the pending count wrapping to zero. I.E. it should stick at 0xFFFF > >> > and not wrap to 0. > >> > >> This commit mail is rather old, and this fix was incorrect, because > >> the task cannot be referenced after it has been run. Some task > >> handlers will free the task as part of the handler. > > > > Ok, maybe the e-mail got stuck somewhere. Have you fixed the above > > mentioned issues in a newer patch? > > If you look at the file history for subr_taskqueue.c: > > http://svn.freebsd.org/viewvc/base/head/sys/kern/subr_taskqueue.c > > You will see quite a few commits by me. The most recent relating to > detecting if a task is running is being MFC'd today: Yes, and I see that this code needs an overflow check, which is one of the issues still not fixed: Before: /* * Count multiple enqueues. */ if (task->ta_pending) { task->ta_pending++; TQ_UNLOCK(queue); return 0; } After: /* * Count multiple enqueues. */ if (task->ta_pending) { if (task->ta_pending != 0xFFFF) task->ta_pending++; TQ_UNLOCK(queue); return 0; } Else the ta_pending can wrap to zero and the code will not do what it announces it does. --HPS