From: Sebastien Dugue <sebastien.dugue@bull•net>
To: michael@ellerman•id.au
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
Subject: Re: [PATCH] powerpc - Initialize the irq radix tree earlier
Date: Thu, 31 Jul 2008 15:26:06 +0200 [thread overview]
Message-ID: <20080731152606.5ae7c379@bull.net> (raw)
In-Reply-To: <1217509299.19050.15.camel@localhost>
On Thu, 31 Jul 2008 23:01:39 +1000 Michael Ellerman <michael@ellerman•id.au=
> wrote:
> 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 <michael@ellerman=
.id.au> 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 =
yet?
> > >=20
> > > It's hairy, I agree, but as you've mentioned no one has done a requ=
est_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 th=
e first
> > check here:
>=20
> @#$% ctrl-enter =3D=3D send!
>=20
> Continuing ...
>=20
> void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
> {
> unsigned int height, shift;
> struct radix_tree_node *node, **slot;
>=20
> node =3D rcu_dereference(root->rnode);
> if (node =3D=3D NULL)
> return NULL;
>=20
> Which means =EF=BB=BFirq_radix_revmap_lookup() will return NO_IRQ, which =
is cool.
Which is what I intended so that as long as no IRQ is registered we
return NO_IRQ.
>=20
>=20
> 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.
That's true as no IRQs are registered before smp_xics_probe() and for any
interrupt we might get before that, irq_radix_revmap_lookup() will return
NO_IRQ.
Thanks,
Sebastien.
next prev parent reply other threads:[~2008-07-31 13:25 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-07-31 9:40 [PATCH 0/3] powerpc - Make the irq reverse mapping tree lockless Sebastien Dugue
2008-07-31 9:40 ` [PATCH] powerpc - Initialize the irq radix tree earlier Sebastien Dugue
2008-07-31 11:40 ` Michael Ellerman
2008-07-31 12:00 ` Sebastien Dugue
2008-07-31 12:10 ` Sebastien Dugue
2008-07-31 12:58 ` Michael Ellerman
2008-07-31 13:01 ` Michael Ellerman
2008-07-31 13:26 ` Sebastien Dugue [this message]
2008-07-31 13:39 ` Michael Ellerman
2008-07-31 14:14 ` Sebastien Dugue
2008-07-31 9:40 ` [PATCH] powerpc - Separate the irq radix tree insertion and lookup Sebastien Dugue
2008-07-31 9:40 ` [PATCH] powerpc - Make the irq reverse mapping radix tree lockless Sebastien Dugue
2008-07-31 10:12 ` [PATCH 0/3] powerpc - Make the irq reverse mapping " Sebastien Dugue
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