From owner-freebsd-current@FreeBSD.ORG Tue Apr 10 14:38:55 2012 Return-Path: Delivered-To: current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 34132106564A; Tue, 10 Apr 2012 14:38:55 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from mail.zoral.com.ua (mx0.zoral.com.ua [91.193.166.200]) by mx1.freebsd.org (Postfix) with ESMTP id 901BE8FC18; Tue, 10 Apr 2012 14:38:54 +0000 (UTC) Received: from skuns.kiev.zoral.com.ua (localhost [127.0.0.1]) by mail.zoral.com.ua (8.14.2/8.14.2) with ESMTP id q3AEcZkK056263; Tue, 10 Apr 2012 17:38:35 +0300 (EEST) (envelope-from kostikbel@gmail.com) Received: from deviant.kiev.zoral.com.ua (kostik@localhost [127.0.0.1]) by deviant.kiev.zoral.com.ua (8.14.5/8.14.5) with ESMTP id q3AEcZ2x095469; Tue, 10 Apr 2012 17:38:35 +0300 (EEST) (envelope-from kostikbel@gmail.com) Received: (from kostik@localhost) by deviant.kiev.zoral.com.ua (8.14.5/8.14.5/Submit) id q3AEcZxs095468; Tue, 10 Apr 2012 17:38:35 +0300 (EEST) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: deviant.kiev.zoral.com.ua: kostik set sender to kostikbel@gmail.com using -f Date: Tue, 10 Apr 2012 17:38:35 +0300 From: Konstantin Belousov To: John Baldwin Message-ID: <20120410143835.GZ2358@deviant.kiev.zoral.com.ua> References: <20120407125056.GS2358@deviant.kiev.zoral.com.ua> <201204091536.08399.jhb@freebsd.org> <20120409200529.GT2358@deviant.kiev.zoral.com.ua> <201204100956.06750.jhb@freebsd.org> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="1KpuWNmRW3f9lK5a" Content-Disposition: inline In-Reply-To: <201204100956.06750.jhb@freebsd.org> User-Agent: Mutt/1.4.2.3i X-Virus-Scanned: clamav-milter 0.95.2 at skuns.kiev.zoral.com.ua X-Virus-Status: Clean X-Spam-Status: No, score=-4.0 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00 autolearn=ham version=3.2.5 X-Spam-Checker-Version: SpamAssassin 3.2.5 (2008-06-10) on skuns.kiev.zoral.com.ua Cc: Ian Lepore , freebsd-drivers@freebsd.org, current@freebsd.org Subject: Re: device_attach(9) and driver initialization 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: Tue, 10 Apr 2012 14:38:55 -0000 --1KpuWNmRW3f9lK5a Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Apr 10, 2012 at 09:56:06AM -0400, John Baldwin wrote: > On Monday, April 09, 2012 4:05:29 pm Konstantin Belousov wrote: > > On Mon, Apr 09, 2012 at 03:36:08PM -0400, John Baldwin wrote: > > > On Monday, April 09, 2012 3:10:00 pm Konstantin Belousov wrote: > > > > On Mon, Apr 09, 2012 at 11:01:03AM -0400, John Baldwin wrote: > > > > > On Saturday, April 07, 2012 11:08:41 pm Warner Losh wrote: > > > > > >=20 > > > > > > On Apr 7, 2012, at 8:46 AM, Ian Lepore wrote: > > > > > >=20 > > > > > > > On Sat, 2012-04-07 at 15:50 +0300, Konstantin Belousov wrote: > > > > > > >> Hello, > > > > > > >> there seems to be a problem with device attach sequence offe= red by=20 > > > > > newbus. > > > > > > >> Basically, when device attach method is executing, device is= not fully > > > > > > >> initialized yet. Also the device state in the newbus part of= the world > > > > > > >> is DS_ALIVE. There is definitely no shattering news in the s= tatements, > > > > > > >> but drivers that e.g. create devfs node to communicate with = consumers > > > > > > >> are prone to a race. > > > > > > >>=20 > > > > > > >> If /dev node is created inside device attach method, then us= ermode > > > > > > >> can start calling cdevsw methods before device fully initial= ized itself. > > > > > > >> Even more, if device tries to use newbus helpers in cdevsw m= ethods, > > > > > > >> like device_busy(9), then panic occurs "called for unatteche= d device". > > > > > > >> I get reports from users about this issues, to it is not som= ething > > > > > > >> that only could happen. > > > > > > >>=20 > > > > > > >> I propose to add DEVICE_AFTER_ATTACH() driver method, to be = called > > > > > > >> from newbus right after device attach finished and newbus co= nsiders > > > > > > >> the device fully initialized. Driver then could create devfs= node > > > > > > >> in the after_attach method instead of attach. Please see the= patch below. > > > > > > >>=20 > > > > > > >> diff --git a/sys/kern/device_if.m b/sys/kern/device_if.m > > > > > > >> index eb720eb..9db74e2 100644 > > > > > > >> --- a/sys/kern/device_if.m > > > > > > >> +++ b/sys/kern/device_if.m > > > > > > >> @@ -43,6 +43,10 @@ INTERFACE device; > > > > > > >> # Default implementations of some methods. > > > > > > >> # > > > > > > >> CODE { > > > > > > >> + static void null_after_attach(device_t dev) > > > > > > >> + { > > > > > > >> + } > > > > > > >> + > > > > > > >> static int null_shutdown(device_t dev) > > > > > > >> { > > > > > > >> return 0; > > > > > > >> @@ -199,6 +203,21 @@ METHOD int attach { > > > > > > >> }; > > > > > > >>=20 > > > > > > >> /** > > > > > > >> + * @brief Notify the driver that device is in attached state > > > > > > >> + * > > > > > > >> + * Called after driver is successfully attached to the devi= ce and > > > > > > >> + * corresponding device_t is fully operational. Driver now = may expose > > > > > > >> + * the device to the consumers, e.g. create devfs nodes. > > > > > > >> + * > > > > > > >> + * @param dev the device to probe > > > > > > >> + * > > > > > > >> + * @see DEVICE_ATTACH() > > > > > > >> + */ > > > > > > >> +METHOD void after_attach { > > > > > > >> + device_t dev; > > > > > > >> +} DEFAULT null_after_attach; > > > > > > >> + > > > > > > >> +/** > > > > > > >> * @brief Detach a driver from a device. > > > > > > >> * > > > > > > >> * This can be called if the user is replacing the > > > > > > >> diff --git a/sys/kern/subr_bus.c b/sys/kern/subr_bus.c > > > > > > >> index d485b9f..6d849cb 100644 > > > > > > >> --- a/sys/kern/subr_bus.c > > > > > > >> +++ b/sys/kern/subr_bus.c > > > > > > >> @@ -2743,6 +2743,7 @@ device_attach(device_t dev) > > > > > > >> dev->state =3D DS_ATTACHED; > > > > > > >> dev->flags &=3D ~DF_DONENOMATCH; > > > > > > >> devadded(dev); > > > > > > >> + DEVICE_AFTER_ATTACH(dev); > > > > > > >> return (0); > > > > > > >> } > > > > > > >>=20 > > > > > > >=20 > > > > > > > Does device_get_softc() work before attach is completed? (I = don't have > > > > > > > time to go look in the code right now). If so, then a mutex = initialized > > > > > > > and acquired early in the driver's attach routine, and also a= cquired in > > > > > > > the driver's cdev implementation routines before using any ne= wbus > > > > > > > functions other than device_get_softc(), would solve the prob= lem without > > > > > > > a driver api change that would make it harder to backport/MFC= driver > > > > > > > changes. > > > > > >=20 > > > > > > Also, more generally, don't create the dev nodes before you are= ready to=20 > > > > > deal with requests. Why do we need to uglify everything here? I= f you can't=20 > > > > > do that, you can check a bit in the softc and return EBUSY or ENX= IO on open if=20 > > > > > that bit says that your driver isn't ready to accept requests. > > > > >=20 > > > > > I agree, this dosen't actually fix anything as the decision for w= hat to put > > > > > in your foo_attach() method rather than foo_after_attach() is non= -obvious and=20 > > > > > very arbitrary. > > > > >=20 > > > > > The actual bug appears to only be with using 'device_busy()'. I t= hink > > > > > this should be fixed by making device_busy() better, not by adding > > > > > this type of obfuscation to attach. It should be trivial to make > > > > > device_busy() safe to use on a device that is currently being att= ached > > > > > which will not require any changes to drivers. > > > >=20 > > > > Could you, please, elaborate your proposal ? How do you think devic= e_busy() > > > > can be enchanced ? > > > >=20 > > > > Obvious idea to sleep inside device_busy() until dev->state becomes= !=3D > > > > DS_ATTACHED is no go, IMO. The issue is that this causes immediate = deadlocks > > > > if device_attach() method needs to call destroy_dev() to rollback. > > >=20 > > > I think you could have a DS_ATTACHING state and allow device_busy() t= o work > > > for DS_ATTACHING. The idea being that it is a bug for a driver to in= voke > > > device_busy() if it is going to fail attach. You may then need to do= a fixup > > > in device_attach() to promote the state from DS_ATTACHED to DS_BUSY w= hen it > > > returns if there is a non-zero busy count. > > This is quite good idea, but it still adds burden to device author, > > although I agree that this is manageable. A scenario I have in mind now > > is the following: > > assume that driver needs to create two devfs nodes, lets name them > > dri/card0 and dri/forcewake0. Driver would perform two make_dev_p(9) > > calls, and while creation of dri/card0 succeed, consequent creation > > of dri/forcewake0 could fail for numerous reasons. > >=20 > > Now, the driver needs to ensure that cdesvw->d_open() on dri/card0 > > would return ENXIO until dri/forcewake0 is created. This can be impleme= nted > > with flag, indeed. But still somewhat muddy, and probably leads to > > user-visible errors (I mostly worry about graphical login managers). >=20 > You could also sleep on the flag in d_open() (you can imagine a two-step > process where you set a "adding cdev's flag", then all d_open() calls blo= ck > on it). Then when finished adding cdev's, you set a flag if an error > occurred and wake up all the waiters. If no error occured the waiters can > have the first open() work fine. But even with other proposals you still > have to deal with this problem if you want to fail out entirely if you > have problems creating cdevs. >=20 > > But for single-node drivers it is indeed a nice solution. >=20 > I think we are somewhat stuck with this for other reasons as well. Note > that device_busy() propagates up the tree to parent devices, so imagine > kldloading a driver that creates a tree (e.g. a bus with a few consumers) > where the leaf devices are attached by a call to bus_generic_attach() from > the device_attach() method for the parent device. Even if you add a > DEVICE_AFTER_ATTACH() hook, while it may allow device_busy() to be invoked > on the leaf device, when it tries to propagate device_busy() up to the > parent device it would still be in the middle of attach and blow up anywa= y. This looks like a bug in my implementation of after_attach, which apparently should be called for new tree after the top level attach finished. Anyway, would you commit your change ? I definitely can work out the driver change after. But this seems to be a large amount of work for driver authors. --1KpuWNmRW3f9lK5a Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (FreeBSD) iEYEARECAAYFAk+EReoACgkQC3+MBN1Mb4g2oACg5H8O707oiuR1k1MaptmwgEJQ gM4An2WDMk7DX3F8qFaA2HzvGTPLJeXs =R09x -----END PGP SIGNATURE----- --1KpuWNmRW3f9lK5a--