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SubjectRe: [PATCH 00/11] rcu: Add missing RCU idle APIs on idle loop v2
On 26/08/12 04:18, Paul E. McKenney wrote:
> On Sat, Aug 25, 2012 at 03:16:49PM +0200, Frederic Weisbecker wrote:
>> On Fri, Aug 24, 2012 at 08:50:47PM -0700, Paul E. McKenney wrote:
>>> On Sat, Aug 25, 2012 at 02:19:14AM +0100, Ben Hutchings wrote:
>>>> On Fri, 2012-08-24 at 14:26 -0700, Paul E. McKenney wrote:
>>>>> On Thu, Aug 23, 2012 at 04:58:24PM +0200, Frederic Weisbecker wrote:
>>>>>> Hi,
>>>>>>
>>>>>> Changes since v1:
>>>>>>
>>>>>> - Fixed preempt handling in alpha idle loop
>>>>>> - added ack from Geert
>>>>>> - fixed stable email address, sorry :-/
>>>>>>
>>>>>> This time I built tested everywhere but: h8300 (compiler internal error),
>>>>>> and mn10300, parisc, score (cross compilers not available in
>>>>>> ftp://ftp.kernel.org/pub/tools/crosstool/files/bin/x86_64/4.6.3/)
>>>>>>
>>>>>> For testing, you can pull from:
>>>>>>
>>>>>> git://github.com/fweisbec/linux-dynticks.git
>>>>>> rcu/idle-fix-v2
>>>>>>
>>>>>> Thanks.
>>>>>
>>>>> I have queued these on -rcu branch rcu/idle:
>>>>>
>>>>> git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
>>>>>
>>>>> This problem has been in place since 3.3, so it is hard to argue that
>>>>> it is a regression for this merge window. I have therefore queued it
>>>>> for 3.7.
>>>>
>>>> I don't follow that; I would expect any serious bug fix (serious enough
>>>> for a stable update) to be acceptable for 3.6 at this point.
>>>
>>> OK, if any of the arch maintainers wishes to submit the patch to 3.6,
>>> they are free to do so -- just let me know and I will drop the patch from
>>> my tree.
>>>
>>> That said, all this does is cause spurious warnings to be printed, so
>>> not sure it really qualifies as serious. But I am happy to leave that
>>> decision with the individual arch maintainers -- it is their arch,
>>> after all, so their decision.
>>
>> Couldn't that cause hung tasks due to long lasting synchronize_rcu() ?
>
> In theory, definitely. In practice, they haven't been running into it,
> or they would be reporting hangs.

I am hereby reporting that RCU CPU stall warnings and hung tasks are
being experienced on SMP kernels built for generic Alpha. This problem
dates back quite a few kernel releases. The discussed patches appear to
fix the problem.

A backport to the 3.2 kernel, of at least the Alpha patches, would be
very much appreciated! :-)

Cheers
Michael.


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