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SubjectRe: Linux 3.16-rc6
On Thu, Jul 24, 2014 at 11:18:16AM -0700, Linus Torvalds wrote:
> On Thu, Jul 24, 2014 at 5:58 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > So going by the nifty picture rostedt made:
> >
> > [ 61.454336] CPU0 CPU1
> > [ 61.454336] ---- ----
> > [ 61.454336] lock(&(&p->alloc_lock)->rlock);
> > [ 61.454336] local_irq_disable();
> > [ 61.454336] lock(tasklist_lock);
> > [ 61.454336] lock(&(&p->alloc_lock)->rlock);
> > [ 61.454336] <Interrupt>
> > [ 61.454336] lock(tasklist_lock);
>
> So this *should* be fine. It always has been in the past, and it was
> certainly the *intention* that it should continue to work with
> qrwlock, even in the presense of pending writers on other cpu's.
>
> The qrwlock rules are that a read-lock in an interrupt is still going
> to be unfair and succeed if there are other readers.

Ah, indeed. Should have checked :/

> So it sounds to me like the new lockdep rules in tip/master are too
> strict and are throwing a false positive.

Right. Waiman can you have a look?


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