From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [PATCH] powerpc - Initialize the irq radix tree earlier From: Michael Ellerman To: Sebastien Dugue In-Reply-To: <1217509104.19050.11.camel@localhost> References: <1217497241-10685-1-git-send-email-sebastien.dugue@bull.net> <1217497241-10685-2-git-send-email-sebastien.dugue@bull.net> <1217504456.9817.22.camel@localhost> <20080731140002.31bbe4a0@bull.net> <1217509104.19050.11.camel@localhost> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="=-BpWQhTys3bQsJZuJJpkn" Date: Thu, 31 Jul 2008 23:01:39 +1000 Message-Id: <1217509299.19050.15.camel@localhost> Mime-Version: 1.0 Cc: tinytim@us.ibm.com, linux-rt-users@vger.kernel.org, jean-pierre.dion@bull.net, rostedt@goodmis.org, linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org, paulus@samba.org, gilles.carry@ext.bull.net, tglx@linutronix.de Reply-To: michael@ellerman.id.au List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , --=-BpWQhTys3bQsJZuJJpkn Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On Thu, 2008-07-31 at 22:58 +1000, Michael Ellerman wrote: > On Thu, 2008-07-31 at 14:00 +0200, Sebastien Dugue wrote: > > On Thu, 31 Jul 2008 21:40:56 +1000 Michael Ellerman wrote: > > >=20 > > > This boot ordering stuff is pretty hairy, so I might have missed > > > something, but this is how the code is ordered AFAICT: > > > =EF=BB=BF > > > start_kernel() > > > init_IRQ() > > > ... > > > local_irq_enable() > > > ... > > > rest_init() > > > kernel_thread() > > > kernel_init() > > > smp_prepare_cpus() > > > smp_xics_probe() (via smp_ops->probe()) > > >=20 > > >=20 > > > What's stopping us from taking an irq between local_irq_enable() and > > > smp_xics_probe() ? Is it just that no one's request_irq()'ed them ye= t? > >=20 > > It's hairy, I agree, but as you've mentioned no one has done a reques= t_irq() > > at that point. The first one to do it is smp_xics_probe() for the IPI. >=20 > Hmm, I don't think that's strong enough. I can trivially cause irqs to > fire during a kexec reboot just by mashing the keyboard. >=20 > And during a kdump boot all sorts of stuff could be firing. Even during > a clean boot, from firmware, I don't think we can guarantee that > nothing's going to fire. >=20 > .. after a bit of testing .. >=20 > It seems it actually works (sort of).=20 >=20 > xics_remap_irq() calls irq_radix_revmap_lookup(), which calls: >=20 > ptr =3D radix_tree_lookup(&host->revmap_data.tree, hwirq); >=20 > And because =EF=BB=BFhost->revmap_data.tree was zalloc'ed we trip on the = first > check here: @#$% ctrl-enter =3D=3D send! Continuing ... void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index) { unsigned int height, shift; struct radix_tree_node *node, **slot; node =3D rcu_dereference(root->rnode); if (node =3D=3D NULL) return NULL; Which means =EF=BB=BFirq_radix_revmap_lookup() will return NO_IRQ, which is= cool. So I think it can fly, as long as we're happy that we can't reverse map anything until smp_xics_probe() - and I think that's true, as any irq we take will be invalid. cheers --=20 Michael Ellerman OzLabs, IBM Australia Development Lab wwweb: http://michael.ellerman.id.au phone: +61 2 6212 1183 (tie line 70 21183) We do not inherit the earth from our ancestors, we borrow it from our children. - S.M.A.R.T Person --=-BpWQhTys3bQsJZuJJpkn Content-Type: application/pgp-signature; name=signature.asc Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) iD8DBQBIkbezdSjSd0sB4dIRAkisAJsHzgyg5HoFJkP7Re4K4x+cY9A2XACgq8YY uk3cPoEt5eWGPqvfhs/YxrI= =vBiQ -----END PGP SIGNATURE----- --=-BpWQhTys3bQsJZuJJpkn--