Re: futex funkiness -- massive lockups

[Linus Torvalds]

On Tue, Mar 4, 2014 at 5:43 PM, Davidlohr Bueso <davidlohr@xxxxxx> wrote:
>
>
> From the paths related to futex wait we are stuck when taking the hb
> spinlock in futex_wait_setup >> queue_lock.

Just judging from your trace, I would have suspected a (possibly soft)
lockup in load_balance() rather than the futexes.

The futex being stuck seems expected, since one cpu is definitely
holding the lock - it was interrupted by a timer interrupt at the
successful return case of raw_spin_lock if I read the offset right.

So if that softirq is stuck - perhaps because it's in some endless
loop in load_balance(), or perhaps because it's spending so much time
load-balancing that the next balancing time happens immediately, or
whatever - then you'd see that trace.

              Linus
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