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 Hałasa <khal...@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.
thanks
-john
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