Re: [PATCH next v2] OF: convert devtree lock from rw_lock to raw spinlock

Re: [PATCH next v2] OF: convert devtree lock from rw_lock to raw spinlock

[Stephen Warren]

On 02/08/2013 04:09 PM, Rob Herring wrote:
> On 02/06/2013 02:30 PM, Paul Gortmaker wrote:
>> From: Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>
>>
>> With the locking cleanup in place (from "OF: Fixup resursive
>> locking code paths"), we can now do the conversion from the
>> rw_lock to a raw spinlock as required for preempt-rt.
>>
>> The previous cleanup and this conversion were originally
>> separate since they predated when mainline got raw spinlock (in
>> commit c2f21ce2e31286a "locking: Implement new raw_spinlock").
>>
>> So, at that point in time, the cleanup was considered plausible
>> for mainline, but not this conversion.  In any case, we've kept
>> them separate as it makes for easier review and better bisection.
>>
>> Signed-off-by: Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>
>> [PG: taken from preempt-rt, update subject & add a commit log]
>> Signed-off-by: Paul Gortmaker <paul.gortmaker-CWA4WttNNZF54TAoqtyWWQ@public.gmane.org>
>> ---
>>
>> [v2: recent commit e81b329 ("powerpc+of: Add /proc device tree
>>  updating to of node add/remove") added two more instances of
>>  write_unlock that also needed converting to raw_spin_unlock.
>>  Retested (boot) on sbc8548, defconfig builds on arm/sparc; no
>>  new warnings observed.]
>>
>>  arch/sparc/kernel/prom_common.c |   4 +-
>>  drivers/of/base.c               | 100 ++++++++++++++++++++++------------------
>>  include/linux/of.h              |   2 +-
>>  3 files changed, 59 insertions(+), 47 deletions(-)
> 
> Applied.

This commit is present in next-20130211, and causes a boot failure
(hang) early while booting on Tegra. Reverting just this one commit
solves the issue.

I'll see if I can track down where the issue is. Given the commit
description, I assume there's some new recursive lock issue that snuck
in between the previous fix for them and this commit? Any hints welcome.

One thing I wonder looking at the patch: Most paths use
raw_spin_lock_irqsave() but a few use just raw_spin_lock(). I wonder how
that decision was made?

Re: [PATCH next v2] OF: convert devtree lock from rw_lock to raw spinlock

[Rob Herring]

On 02/11/2013 01:29 PM, Stephen Warren wrote:
> On 02/08/2013 04:09 PM, Rob Herring wrote:
>> On 02/06/2013 02:30 PM, Paul Gortmaker wrote:
>>> From: Thomas Gleixner <tglx@linutronix.de>
>>>
>>> With the locking cleanup in place (from "OF: Fixup resursive
>>> locking code paths"), we can now do the conversion from the
>>> rw_lock to a raw spinlock as required for preempt-rt.
>>>
>>> The previous cleanup and this conversion were originally
>>> separate since they predated when mainline got raw spinlock (in
>>> commit c2f21ce2e31286a "locking: Implement new raw_spinlock").
>>>
>>> So, at that point in time, the cleanup was considered plausible
>>> for mainline, but not this conversion.  In any case, we've kept
>>> them separate as it makes for easier review and better bisection.
>>>
>>> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>>> [PG: taken from preempt-rt, update subject & add a commit log]
>>> Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
>>> ---
>>>
>>> [v2: recent commit e81b329 ("powerpc+of: Add /proc device tree
>>>  updating to of node add/remove") added two more instances of
>>>  write_unlock that also needed converting to raw_spin_unlock.
>>>  Retested (boot) on sbc8548, defconfig builds on arm/sparc; no
>>>  new warnings observed.]
>>>
>>>  arch/sparc/kernel/prom_common.c |   4 +-
>>>  drivers/of/base.c               | 100 ++++++++++++++++++++++------------------
>>>  include/linux/of.h              |   2 +-
>>>  3 files changed, 59 insertions(+), 47 deletions(-)
>>
>> Applied.
> 
> This commit is present in next-20130211, and causes a boot failure
> (hang) early while booting on Tegra. Reverting just this one commit
> solves the issue.
> 
> I'll see if I can track down where the issue is. Given the commit
> description, I assume there's some new recursive lock issue that snuck
> in between the previous fix for them and this commit? Any hints welcome.
> 
> One thing I wonder looking at the patch: Most paths use
> raw_spin_lock_irqsave() but a few use just raw_spin_lock(). I wonder how
> that decision was made?

I found the problem. of_get_next_available_child ->
of_device_is_available -> of_get_property -> of_get_property. An
unlocked version of of_device_is_available is needed here.

Rob

Re: [PATCH next v2] OF: convert devtree lock from rw_lock to raw spinlock

[Grant Likely]

On Mon, Feb 11, 2013 at 7:54 PM, Rob Herring <robherring2@gmail.com> wrote:
> On 02/11/2013 01:29 PM, Stephen Warren wrote:
>> On 02/08/2013 04:09 PM, Rob Herring wrote:
>>> On 02/06/2013 02:30 PM, Paul Gortmaker wrote:
>>>> From: Thomas Gleixner <tglx@linutronix.de>
>>>>
>>>> With the locking cleanup in place (from "OF: Fixup resursive
>>>> locking code paths"), we can now do the conversion from the
>>>> rw_lock to a raw spinlock as required for preempt-rt.
>>>>
>>>> The previous cleanup and this conversion were originally
>>>> separate since they predated when mainline got raw spinlock (in
>>>> commit c2f21ce2e31286a "locking: Implement new raw_spinlock").
>>>>
>>>> So, at that point in time, the cleanup was considered plausible
>>>> for mainline, but not this conversion.  In any case, we've kept
>>>> them separate as it makes for easier review and better bisection.
>>>>
>>>> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>>>> [PG: taken from preempt-rt, update subject & add a commit log]
>>>> Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
>>>> ---
>>>>
>>>> [v2: recent commit e81b329 ("powerpc+of: Add /proc device tree
>>>>  updating to of node add/remove") added two more instances of
>>>>  write_unlock that also needed converting to raw_spin_unlock.
>>>>  Retested (boot) on sbc8548, defconfig builds on arm/sparc; no
>>>>  new warnings observed.]
>>>>
>>>>  arch/sparc/kernel/prom_common.c |   4 +-
>>>>  drivers/of/base.c               | 100 ++++++++++++++++++++++------------------
>>>>  include/linux/of.h              |   2 +-
>>>>  3 files changed, 59 insertions(+), 47 deletions(-)
>>>
>>> Applied.
>>
>> This commit is present in next-20130211, and causes a boot failure
>> (hang) early while booting on Tegra. Reverting just this one commit
>> solves the issue.
>>
>> I'll see if I can track down where the issue is. Given the commit
>> description, I assume there's some new recursive lock issue that snuck
>> in between the previous fix for them and this commit? Any hints welcome.
>>
>> One thing I wonder looking at the patch: Most paths use
>> raw_spin_lock_irqsave() but a few use just raw_spin_lock(). I wonder how
>> that decision was made?
>
> I found the problem. of_get_next_available_child ->
> of_device_is_available -> of_get_property -> of_get_property. An
> unlocked version of of_device_is_available is needed here.

Oops, I had testbooted on a single core machine which would mask the
issue. I've crafted a fix and am posting it for review before I apply
it.

g.

Re: [PATCH next v2] OF: convert devtree lock from rw_lock to raw spinlock

[Rob Herring]

On 02/11/2013 04:18 PM, Grant Likely wrote:
> On Mon, Feb 11, 2013 at 7:54 PM, Rob Herring <robherring2@gmail.com> wrote:
>> On 02/11/2013 01:29 PM, Stephen Warren wrote:
>>> On 02/08/2013 04:09 PM, Rob Herring wrote:
>>>> On 02/06/2013 02:30 PM, Paul Gortmaker wrote:
>>>>> From: Thomas Gleixner <tglx@linutronix.de>
>>>>>
>>>>> With the locking cleanup in place (from "OF: Fixup resursive
>>>>> locking code paths"), we can now do the conversion from the
>>>>> rw_lock to a raw spinlock as required for preempt-rt.
>>>>>
>>>>> The previous cleanup and this conversion were originally
>>>>> separate since they predated when mainline got raw spinlock (in
>>>>> commit c2f21ce2e31286a "locking: Implement new raw_spinlock").
>>>>>
>>>>> So, at that point in time, the cleanup was considered plausible
>>>>> for mainline, but not this conversion.  In any case, we've kept
>>>>> them separate as it makes for easier review and better bisection.
>>>>>
>>>>> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>>>>> [PG: taken from preempt-rt, update subject & add a commit log]
>>>>> Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
>>>>> ---
>>>>>
>>>>> [v2: recent commit e81b329 ("powerpc+of: Add /proc device tree
>>>>>  updating to of node add/remove") added two more instances of
>>>>>  write_unlock that also needed converting to raw_spin_unlock.
>>>>>  Retested (boot) on sbc8548, defconfig builds on arm/sparc; no
>>>>>  new warnings observed.]
>>>>>
>>>>>  arch/sparc/kernel/prom_common.c |   4 +-
>>>>>  drivers/of/base.c               | 100 ++++++++++++++++++++++------------------
>>>>>  include/linux/of.h              |   2 +-
>>>>>  3 files changed, 59 insertions(+), 47 deletions(-)
>>>>
>>>> Applied.
>>>
>>> This commit is present in next-20130211, and causes a boot failure
>>> (hang) early while booting on Tegra. Reverting just this one commit
>>> solves the issue.
>>>
>>> I'll see if I can track down where the issue is. Given the commit
>>> description, I assume there's some new recursive lock issue that snuck
>>> in between the previous fix for them and this commit? Any hints welcome.
>>>
>>> One thing I wonder looking at the patch: Most paths use
>>> raw_spin_lock_irqsave() but a few use just raw_spin_lock(). I wonder how
>>> that decision was made?
>>
>> I found the problem. of_get_next_available_child ->
>> of_device_is_available -> of_get_property -> of_get_property. An
>> unlocked version of of_device_is_available is needed here.
> 
> Oops, I had testbooted on a single core machine which would mask the
> issue. I've crafted a fix and am posting it for review before I apply
> it.
> 

I'm in the process of applying Stephen's fix.

Rob

Re: [PATCH next v2] OF: convert devtree lock from rw_lock to raw spinlock

[Grant Likely]

On Mon, Feb 11, 2013 at 10:21 PM, Rob Herring <robherring2@gmail.com> wrote:
> On 02/11/2013 04:18 PM, Grant Likely wrote:
>> On Mon, Feb 11, 2013 at 7:54 PM, Rob Herring <robherring2@gmail.com> wrote:
>>> I found the problem. of_get_next_available_child ->
>>> of_device_is_available -> of_get_property -> of_get_property. An
>>> unlocked version of of_device_is_available is needed here.
>>
>> Oops, I had testbooted on a single core machine which would mask the
>> issue. I've crafted a fix and am posting it for review before I apply
>> it.
>>
>
> I'm in the process of applying Stephen's fix.

I didn't actually see Stephen's fix until just now, after I had
already written, posted and pushed out basically the same thing. :-)

g.