linux-kernel - Re: [PATCH next v2] OF: convert devtree lock from rw

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Date:	Mon, 11 Feb 2013 22:18:32 +0000
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Rob Herring <robherring2@...il.com>
Cc:	Stephen Warren <swarren@...dotorg.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	rt-users <linux-rt-users@...r.kernel.org>,
	devicetree-discuss <devicetree-discuss@...ts.ozlabs.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	sparclinux@...r.kernel.org, Sam Ravnborg <sam@...nborg.org>,
	"linux-next@...r.kernel.org" <linux-next@...r.kernel.org>
Subject: Re: [PATCH next v2] OF: convert devtree lock from rw_lock to raw spinlock

On Mon, Feb 11, 2013 at 7:54 PM, Rob Herring <robherring2@...il.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@...utronix.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@...utronix.de>
>>>> [PG: taken from preempt-rt, update subject & add a commit log]
>>>> Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.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.
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