From owner-freebsd-scsi@FreeBSD.ORG Mon Feb 27 17:47:16 2012 Return-Path: Delivered-To: freebsd-scsi@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 000EE1065676; Mon, 27 Feb 2012 17:47:15 +0000 (UTC) (envelope-from Kashyap.Desai@lsi.com) Received: from na3sys009aog125.obsmtp.com (na3sys009aog125.obsmtp.com [74.125.149.153]) by mx1.freebsd.org (Postfix) with ESMTP id 0A1978FC22; Mon, 27 Feb 2012 17:47:14 +0000 (UTC) Received: from paledge01.lsi.com ([192.19.193.42]) (using TLSv1) by na3sys009aob125.postini.com ([74.125.148.12]) with SMTP ID DSNKT0vBogM8vjOnFIKfu5dDdXBhRqFruvrn@postini.com; Mon, 27 Feb 2012 09:47:15 PST Received: from PALCAS01.lsi.com (128.94.213.117) by PALEDGE01.lsi.com (192.19.193.42) with Microsoft SMTP Server (TLS) id 8.3.213.0; Mon, 27 Feb 2012 12:51:50 -0500 Received: from inbexch02.lsi.com (135.36.98.40) by PALCAS01.lsi.com (128.94.213.117) with Microsoft SMTP Server (TLS) id 8.3.213.0; Mon, 27 Feb 2012 12:47:13 -0500 Received: from inbmail01.lsi.com ([135.36.98.64]) by inbexch02.lsi.com ([135.36.98.40]) with mapi; Mon, 27 Feb 2012 23:17:09 +0530 From: "Desai, Kashyap" To: John Baldwin , "freebsd-stable@freebsd.org" Date: Mon, 27 Feb 2012 23:17:07 +0530 Thread-Topic: mpslsi0 : Trying sleep, but thread marked as sleeping prohibited Thread-Index: AczzHWYQfkAel5RkSQGjugGiKVUEJQCWlyqQ Message-ID: References: <20120223092457.GB55074@deviant.kiev.zoral.com.ua> <201202230958.05667.jhb@freebsd.org> In-Reply-To: <201202230958.05667.jhb@freebsd.org> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Cc: "freebsd-scsi@freebsd.org" , "Justin T. Gibbs" , "Kenneth D. Merry" , "McConnell, Stephen" Subject: RE: mpslsi0 : Trying sleep, but thread marked as sleeping prohibited X-BeenThere: freebsd-scsi@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: SCSI subsystem List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 27 Feb 2012 17:47:16 -0000 > -----Original Message----- > From: John Baldwin [mailto:jhb@freebsd.org] > Sent: Thursday, February 23, 2012 8:28 PM > To: freebsd-stable@freebsd.org > Cc: Desai, Kashyap; Konstantin Belousov; freebsd-scsi@freebsd.org; > Kenneth D. Merry; Justin T. Gibbs; McConnell, Stephen > Subject: Re: mpslsi0 : Trying sleep, but thread marked as sleeping > prohibited >=20 > On Thursday, February 23, 2012 8:22:07 am Desai, Kashyap wrote: > > > > > -----Original Message----- > > > From: Konstantin Belousov [mailto:kostikbel@gmail.com] > > > Sent: Thursday, February 23, 2012 2:55 PM > > > To: Desai, Kashyap > > > Cc: freebsd-scsi@freebsd.org; freebsd-stable; Justin T. Gibbs; > Kenneth > > > D. Merry; McConnell, Stephen > > > Subject: Re: mpslsi0 : Trying sleep, but thread marked as sleeping > > > prohibited > > > > > > On Thu, Feb 23, 2012 at 05:52:12AM +0530, Desai, Kashyap wrote: > > > > > > > > > > > > > -----Original Message----- > > > > > From: Konstantin Belousov [mailto:kostikbel@gmail.com] > > > > > Sent: Thursday, February 23, 2012 12:45 AM > > > > > To: Desai, Kashyap > > > > > Cc: freebsd-scsi@freebsd.org; freebsd-stable; Justin T. Gibbs; > > > > > Kenneth D. Merry; McConnell, Stephen > > > > > Subject: Re: mpslsi0 : Trying sleep, but thread marked as > sleeping > > > > > prohibited > > > > > > > > > > On Wed, Feb 22, 2012 at 07:36:42PM +0530, Desai, Kashyap wrote: > > > > > > Hi, > > > > > > > > > > > > I am doing some code changes in mps dirver. While working on > those > > > > > changes, I come to know about something which is new to me. > > > > > > Some expert help is required to clarify my doubt. > > > > > > > > > > > > 1. When any irq is register with FreeBSD OS, it sets " > > > TDP_NOSLEEPING" > > > > > > pflag. It means though irq in freebsd is treated as thread, We > > > > > > cannot > > > > > sleep in IRQ because of " "TDP_NOSLEEPING " set. > > > > > > 2. In mps driver we have below code snippet in ISR routine. > > > > > > > > > > > > > > > > > > mps_dprint(sc, MPS_TRACE, "%s\n", __func__); > > > > > > mps_lock(sc); > > > > > > mps_intr_locked(data); > > > > > > mps_unlock(sc); > > > > > > > > > > > > I wonder why there is no issue with above code ? Theoretical > we > > > > > > cannot sleep in ISR. (as explained in #1) Any thoughts ? > > > > > > > > > > > > > > > > > > 3. I recently added few place msleep() instead of DELAY in ISR > > > > > > context and I see " Trying sleep, but thread marked as > sleeping > > > prohibited". > > > > > > > > > > > FreeBSD has several basic ways to prevent a thread from > executing on > > > > > CPU. > > > > > They mostly fall into two categories: bounded sleep, sometimes > > > > > called blocking, and unbounded sleep, usually abbreviated as > sleep. > > > > > The bounded there refers to amount of code executed by other > thread > > > > > that hold resource preventing blocked thread from making a > progress. > > > > > > > > > > Examples of the blocking primitives are mutexes, rw locks and rm > > > locks. > > > > > The blocking is not counted as sleeping, so interrupt threads, > which > > > > > are designated as non-sleeping, still can lock mutexes. > > > > Thanks for the tech help. . > > > > > > > > As per you comment, So now I understood as "TDP_NOSLEEPING" is > only > > > > for unbounded sleep restriction. Just curious to know, What is a > > > > reason that thread can do blocking sleep but can't do unbounded > sleep > > > > ? Since technically we introduced sleeping restriction on > interrupt > > > > thread is to avoid starvation and that can be fit with either of > the > > > > sleep type. Is this not true ? > > > No, not to avoid starvation. > > > > > > The intent of the blocking primitives is to acquire resources for > > > limited amount of time. In other words, you never take a mutex for > > > undefinitely long computation process. On the other hand, msleep > sleep > > > usually has no limitations. > > > > I got same reply from Ed Schouten. I agree and understood your note. > Thanks > for poring knowledge on this area. > > _but_ only query is when thread take mutex, we don't know when it will > release. So holding time of mutex is really not known. > > In case of some bad code, where thread took mutex and not release > within > short time. This can eventually match upto msleep restriction as well. > > Do we have any checks that thread took long time holding mutext ? > Similar > to linux where spinlock has been not release in some specific time, they > dump > warnings with backtrace. >=20 > We don't allow code to do unbounded sleeps while holding mutexes either, > and > WITNESS warns about doing so. That ensures that barring an infinite > loop-type > bug, mutexes should be held for a bounded amount of time. Thanks. I understood this concept now. Really helpful conversation. >=20 > -- > John Baldwin