From: john.stultz@linaro.org (John Stultz)
To: linux-arm-kernel@lists.infradead.org
Subject: v3.13-rc6+ regression (ARM board)
Date: Thu, 02 Jan 2014 12:52:56 -0800 [thread overview]
Message-ID: <52C5D1A8.8070706@linaro.org> (raw)
In-Reply-To: <52C5CF38.1010704@codeaurora.org>
On 01/02/2014 12:42 PM, Stephen Boyd wrote:
> On 01/02/14 12:30, John Stultz wrote:
>> On 01/02/2014 12:03 PM, John Stultz wrote:
>>> On 01/02/2014 11:38 AM, Linus Torvalds wrote:
>>>> On Thu, Jan 2, 2014 at 4:07 AM, Krzysztof Ha?asa <khalasa@piap.pl> wrote:
>>>>> This means these two commits don't like each other:
>>>>>
>>>>> seqcount: Add lockdep functionality to seqcount/seqlock structures
>>>>> sched_clock: Use seqcount instead of rolling our own
>>>> Does something like this fix it for you?
>>>>
>>>> --- a/kernel/time/sched_clock.c
>>>> +++ b/kernel/time/sched_clock.c
>>>> @@ -36,6 +36,7 @@ core_param(irqtime, irqtime, int, 0400);
>>>>
>>>> static struct clock_data cd = {
>>>> .mult = NSEC_PER_SEC / HZ,
>>>> + .seq = SEQCNT_ZERO(cd.seq),
>>>> };
>>>>
>>>> static u64 __read_mostly sched_clock_mask;
>>>>
>>>> (The above is not even compile-tested, because x86 doesn't use
>>>> GENERIC_SCHED_CLOCK. So I did the patch blindly, but I think you get
>>>> the idea..)
>>> Sheesh. Just finishing up holiday email backlog and Linus already has a
>>> fix. :)
>>>
>>> This looks like it should fix the issue, and does build for me.
>>>
>>> Assuming it works for Krzysztof,
>> So something else may be at play. Even with Linus' patch I reproduced a
>> similar hang here.
>>
>> Still chasing it down, but it looks like a seqlock deadlock where we're
>> calling read while holding the lock.
>>
> Do you have tracing enabled? When I moved this code over to use
> seqcounts it relied on the fact that the compiler wouldn't be generating
> any function calls to the tracing code. Before seqcounts got lockdep
> support it all collapsed down into sched_clock() due to the use of
> inline on the seqlock API.
Hrm. I have tracing compiled in, I'll see if disabling it avoids the issue.
If this is the problem, I'm guessing we may need to change it to use
read_seqcount_begin_no_lockdep() then.
But I still don't have a clear sense of exactly whats happening yet.
thanks
-john
next prev parent reply other threads:[~2014-01-02 20:52 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-31 10:37 v3.13-rc6+ regression (ARM board) Krzysztof Hałasa
2013-12-31 10:45 ` Willy Tarreau
2014-01-02 10:02 ` Krzysztof Hałasa
2014-01-02 10:14 ` Uwe Kleine-König
2014-01-02 12:07 ` Krzysztof Hałasa
2014-01-02 19:38 ` Linus Torvalds
2014-01-02 20:03 ` John Stultz
2014-01-02 20:30 ` John Stultz
2014-01-02 20:42 ` Stephen Boyd
2014-01-02 20:52 ` John Stultz [this message]
2014-01-02 20:43 ` Linus Torvalds
2014-01-02 21:34 ` John Stultz
2014-01-02 21:54 ` [PATCH] sched_clock: Disable seqlock lockdep usage in sched_clock John Stultz
2014-01-02 22:15 ` Linus Torvalds
2014-01-02 22:21 ` John Stultz
2014-01-02 23:11 ` [PATCH 1/2] seqlock: Use raw_ prefix instead of _no_lockdep John Stultz
2014-01-02 23:11 ` [PATCH 2/2] sched_clock: Disable seqlock lockdep usage in sched_clock John Stultz
2014-01-03 0:46 ` Stephen Boyd
2014-01-03 6:05 ` Krzysztof Hałasa
2014-01-03 0:46 ` [PATCH 1/2] seqlock: Use raw_ prefix instead of _no_lockdep Stephen Boyd
2014-01-03 0:50 ` Linus Torvalds
2014-01-04 0:28 ` John Stultz
2014-01-06 10:10 ` Peter Zijlstra
2014-01-03 6:01 ` v3.13-rc6+ regression (ARM board) Krzysztof Hałasa
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