[PATCH 1/2] topology: Check for missing CPU devices

[PATCH 1/2] topology: Check for missing CPU devices

[Ben Hutchings]

Commit ccbc60d3e19a1b6ae66ca0d89b3da02dde62088b ('topology: Provide
CPU topology in sysfs in !SMP configurations') causes a crash at boot
on a several architectures.  The topology sysfs code assumes that
there is a CPU device for each online CPU whereas some architectures
that do not support SMP or cpufreq do not register any CPU devices.
Check for this before trying to use a device.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 drivers/base/topology.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/drivers/base/topology.c b/drivers/base/topology.c
index ae989c5..4467c85 100644
--- a/drivers/base/topology.c
+++ b/drivers/base/topology.c
@@ -147,6 +147,8 @@ static int __cpuinit topology_add_dev(unsigned int cpu)
 {
 	struct device *dev = get_cpu_device(cpu);
 
+	if (!dev)
+		return -ENODEV;
 	return sysfs_create_group(&dev->kobj, &topology_attr_group);
 }
 
@@ -154,7 +156,8 @@ static void __cpuinit topology_remove_dev(unsigned int cpu)
 {
 	struct device *dev = get_cpu_device(cpu);
 
-	sysfs_remove_group(&dev->kobj, &topology_attr_group);
+	if (dev)
+		sysfs_remove_group(&dev->kobj, &topology_attr_group);
 }
 
 static int __cpuinit topology_cpu_callback(struct notifier_block *nfb,
-- 
1.7.8.2

Re: [PATCH 1/2] topology: Check for missing CPU devices

[Linus Torvalds]

Ok, both of the patches look sane to me, but it would really be nice
to hear from somebody with the actual affected architectures, and get
a tested-by.

Testing it on hacked-up x86 sounds fine, but doesn't quite have the
same kind of "yes, this fixes the actual problem" feel to it.

Also, can you clarify: does the second patch make the first patch just
an "irrelevant safety net", or are there possible callers of
topology_add_dev() that could cause problems? I'm just wondering
whether maybe the safety net ends up then possibly hiding some future
bug where we (once more) don't register a cpu and then never really
notice?

Or am I just being difficult?

                     Linus

On Sun, Jan 8, 2012 at 12:48 PM, Ben Hutchings <ben@decadent.org.uk> wrote:
> Commit ccbc60d3e19a1b6ae66ca0d89b3da02dde62088b ('topology: Provide
> CPU topology in sysfs in !SMP configurations') causes a crash at boot
> on a several architectures.  The topology sysfs code assumes that
> there is a CPU device for each online CPU whereas some architectures
> that do not support SMP or cpufreq do not register any CPU devices.
> Check for this before trying to use a device.
>
> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
> ---
>  drivers/base/topology.c |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/base/topology.c b/drivers/base/topology.c
> index ae989c5..4467c85 100644
> --- a/drivers/base/topology.c
> +++ b/drivers/base/topology.c
> @@ -147,6 +147,8 @@ static int __cpuinit topology_add_dev(unsigned int cpu)
>  {
>        struct device *dev = get_cpu_device(cpu);
>
> +       if (!dev)
> +               return -ENODEV;
>        return sysfs_create_group(&dev->kobj, &topology_attr_group);
>  }
>
> @@ -154,7 +156,8 @@ static void __cpuinit topology_remove_dev(unsigned int cpu)
>  {
>        struct device *dev = get_cpu_device(cpu);
>
> -       sysfs_remove_group(&dev->kobj, &topology_attr_group);
> +       if (dev)
> +               sysfs_remove_group(&dev->kobj, &topology_attr_group);
>  }
>
>  static int __cpuinit topology_cpu_callback(struct notifier_block *nfb,
> --
> 1.7.8.2
>
>
>

Re: [PATCH 1/2] topology: Check for missing CPU devices

[richard -rw- weinberger]

On Mon, Jan 9, 2012 at 1:18 AM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> Ok, both of the patches look sane to me, but it would really be nice
> to hear from somebody with the actual affected architectures, and get
> a tested-by.

UML is affected:
https://lkml.org/lkml/2012/1/8/186

I wasted an hour finding out why it is crashing.
Instead of testing kernels I really should read more LKML. ;-)

-- 
Thanks,
//richard

Re: [PATCH 1/2] topology: Check for missing CPU devices

[Linus Torvalds]

On Sun, Jan 8, 2012 at 5:06 PM, richard -rw- weinberger
<richard.weinberger@gmail.com> wrote:
> On Mon, Jan 9, 2012 at 1:18 AM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>> Ok, both of the patches look sane to me, but it would really be nice
>> to hear from somebody with the actual affected architectures, and get
>> a tested-by.
>
> UML is affected:
> https://lkml.org/lkml/2012/1/8/186
>
> I wasted an hour finding out why it is crashing.
> Instead of testing kernels I really should read more LKML. ;-)

Hmm.

Ben - how about that

  static DEFINE_PER_CPU(struct cpu, cpu_devices);

approach that Richard uses in his patch, instead of the kcalloc? And
clearly UM should also do that CONFIG_GENERIC_CPU_DEVICES thing with
your patch.

Richard - does Ben's patch work for  you too if you just add "select
GENERIC_CPU_DEVICES" in the UM Kconfig too (Kconfig.common, probably)?

                      Linus

Re: [PATCH 1/2] topology: Check for missing CPU devices

[Ben Hutchings]

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On Sun, 2012-01-08 at 16:18 -0800, Linus Torvalds wrote:
> Ok, both of the patches look sane to me, but it would really be nice
> to hear from somebody with the actual affected architectures, and get
> a tested-by.
> 
> Testing it on hacked-up x86 sounds fine, but doesn't quite have the
> same kind of "yes, this fixes the actual problem" feel to it.

Indeed.

> Also, can you clarify: does the second patch make the first patch just
> an "irrelevant safety net", or are there possible callers of
> topology_add_dev() that could cause problems? I'm just wondering
> whether maybe the safety net ends up then possibly hiding some future
> bug where we (once more) don't register a cpu and then never really
> notice?
[...]

driver_init() doesn't check that cpu_dev_init() - or any of the other
functions it calls - is successful.  So in theory at least we could boot
and still have no CPU devices after the first patch.

Ben.

-- 
Ben Hutchings
Life is what happens to you while you're busy making other plans.
                                                               - John Lennon

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Re: [PATCH 1/2] topology: Check for missing CPU devices

[Ben Hutchings]

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On Sun, 2012-01-08 at 17:29 -0800, Linus Torvalds wrote:
> On Sun, Jan 8, 2012 at 5:06 PM, richard -rw- weinberger
> <richard.weinberger@gmail.com> wrote:
> > On Mon, Jan 9, 2012 at 1:18 AM, Linus Torvalds
> > <torvalds@linux-foundation.org> wrote:
> >> Ok, both of the patches look sane to me, but it would really be nice
> >> to hear from somebody with the actual affected architectures, and get
> >> a tested-by.
> >
> > UML is affected:
> > https://lkml.org/lkml/2012/1/8/186
> >
> > I wasted an hour finding out why it is crashing.
> > Instead of testing kernels I really should read more LKML. ;-)
> 
> Hmm.
> 
> Ben - how about that
> 
>   static DEFINE_PER_CPU(struct cpu, cpu_devices);
> 
> approach that Richard uses in his patch, instead of the kcalloc?

That seems perfectly good.

> And
> clearly UM should also do that CONFIG_GENERIC_CPU_DEVICES thing with
> your patch.
>
> Richard - does Ben's patch work for  you too if you just add "select
> GENERIC_CPU_DEVICES" in the UM Kconfig too (Kconfig.common, probably)?

Sorry, I meant to cover UM as well but I couldn't see how its Kconfig
files were organised.

Ben.

-- 
Ben Hutchings
Life is what happens to you while you're busy making other plans.
                                                               - John Lennon

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Re: [PATCH 1/2] topology: Check for missing CPU devices

[Ben Hutchings]

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On Mon, 2012-01-09 at 02:47 +0000, Ben Hutchings wrote:
> On Sun, 2012-01-08 at 16:18 -0800, Linus Torvalds wrote:
> > Ok, both of the patches look sane to me, but it would really be nice
> > to hear from somebody with the actual affected architectures, and get
> > a tested-by.
> > 
> > Testing it on hacked-up x86 sounds fine, but doesn't quite have the
> > same kind of "yes, this fixes the actual problem" feel to it.
> 
> Indeed.
> 
> > Also, can you clarify: does the second patch make the first patch just
> > an "irrelevant safety net", or are there possible callers of
> > topology_add_dev() that could cause problems? I'm just wondering
> > whether maybe the safety net ends up then possibly hiding some future
> > bug where we (once more) don't register a cpu and then never really
> > notice?
> [...]
> 
> driver_init() doesn't check that cpu_dev_init() - or any of the other
> functions it calls - is successful.  So in theory at least we could boot
> and still have no CPU devices after the first patch.

I mean to say that we could have no CPU devices after the *second*
patch.  So the first patch is an extra defence against that.  (Though we
could just as well panic if register_cpu() fails at boot time.)

Ben.

-- 
Ben Hutchings
Life is what happens to you while you're busy making other plans.
                                                               - John Lennon

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Re: [PATCH 1/2] topology: Check for missing CPU devices

[Richard Weinberger]

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Am 09.01.2012 03:52, schrieb Ben Hutchings:
> On Sun, 2012-01-08 at 17:29 -0800, Linus Torvalds wrote:
>> On Sun, Jan 8, 2012 at 5:06 PM, richard -rw- weinberger
>> <richard.weinberger@gmail.com> wrote:
>>> On Mon, Jan 9, 2012 at 1:18 AM, Linus Torvalds
>>> <torvalds@linux-foundation.org> wrote:
>>>> Ok, both of the patches look sane to me, but it would really be nice
>>>> to hear from somebody with the actual affected architectures, and get
>>>> a tested-by.
>>>
>>> UML is affected:
>>> https://lkml.org/lkml/2012/1/8/186
>>>
>>> I wasted an hour finding out why it is crashing.
>>> Instead of testing kernels I really should read more LKML. ;-)
>>
>> Hmm.
>>
>> Ben - how about that
>>
>>   static DEFINE_PER_CPU(struct cpu, cpu_devices);
>>
>> approach that Richard uses in his patch, instead of the kcalloc?
> 
> That seems perfectly good.
> 
>> And
>> clearly UM should also do that CONFIG_GENERIC_CPU_DEVICES thing with
>> your patch.
>>
>> Richard - does Ben's patch work for  you too if you just add "select
>> GENERIC_CPU_DEVICES" in the UM Kconfig too (Kconfig.common, probably)?
> 

Yeah, Ben's patch solves the problem too. :-)
Ben, please add the attached patch snippet to your patch.

--

diff --git a/arch/um/Kconfig.common b/arch/um/Kconfig.common
index a923483..b37ae70 100644
--- a/arch/um/Kconfig.common
+++ b/arch/um/Kconfig.common
@@ -8,6 +8,7 @@ config UML
 	default y
 	select HAVE_GENERIC_HARDIRQS
 	select GENERIC_IRQ_SHOW
+	select GENERIC_CPU_DEVICES

 config MMU
 	bool


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Re: [PATCH 1/2] topology: Check for missing CPU devices

[Geert Uytterhoeven]

On Sun, Jan 8, 2012 at 21:48, Ben Hutchings <ben@decadent.org.uk> wrote:
> Commit ccbc60d3e19a1b6ae66ca0d89b3da02dde62088b ('topology: Provide
> CPU topology in sysfs in !SMP configurations') causes a crash at boot
> on a several architectures.  The topology sysfs code assumes that
> there is a CPU device for each online CPU whereas some architectures
> that do not support SMP or cpufreq do not register any CPU devices.
> Check for this before trying to use a device.
>
> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

Thanks!
Works on its own or combined with "[PATCH 2/2] cpu: Register a generic
CPU device on architectures that currently do not".

Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH 1/2] topology: Check for missing CPU devices

[Geert Uytterhoeven]

On Mon, Jan 9, 2012 at 02:06, richard -rw- weinberger
<richard.weinberger@gmail.com> wrote:
> Instead of testing kernels I really should read more LKML. ;-)

As an architecture maintainer, you want to read at least linux-arch.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH 1/2] topology: Check for missing CPU devices

[Linus Torvalds]

On Sun, Jan 8, 2012 at 6:56 PM, Ben Hutchings <ben@decadent.org.uk> wrote:
>
> I mean to say that we could have no CPU devices after the *second*
> patch.  So the first patch is an extra defence against that.  (Though we
> could just as well panic if register_cpu() fails at boot time.)

I think I'd rather just panic - if you have allocation issues during
early boot, the machine is hosed anyway - and then get rid of the
first patch?

Willing to send out a new patch along those lines (and with UML added)?

Thanks,
                  Linus