Re: kernel deadlock
From: Lin Ming
Date: Tue Sep 10 2013 - 04:59:15 EST
On Tue, Sep 10, 2013 at 4:29 AM, John Stultz <john.stultz@xxxxxxxxxx> wrote:
[snip]
>
> So I think I've managed to finally reproduce this and hunt it down.
>
> With Peter's "sched: Fix HRTICK" patch and HRTICK enabled, I found I
> could trigger a hard hang at boot on my x86_64 kvm system. sysrq didn't
> function, so I checked out info cpus and that pointed to both cpus being
Hi,
Is "info cpus" a command of kvm/qemu? That's very helpful.
I can reproduce this bug, but there is no any output.
How did you find out that both cpus being in ktime_get() and
ktime_get_update_offsets().
> in ktime_get() and ktime_get_update_offsets(), which suggested a
> seqcount deadlock (basically calling something that reads the seqlock
> while we hold the write on it).
HRTICK enabled, then I can reproduce this simply with,
while [ 1 ] ;
adjtimex -t 9999
done
And your patch fixed it.
Thanks,
Lin Ming
>
> Unfortunately the seqlock/seqcount infrastructure doesn't support
> lockdep, so I added some debug code to take and release the
> timekeeper_lock in every function that does a read on the timekeeper_seq.
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