Re: [PATCH 32/35] clockevents: Fix cpu down race for hrtimer based broadcasting

From: Nicolas Pitre
Date: Mon Feb 23 2015 - 12:33:21 EST

On Mon, 23 Feb 2015, Nicolas Pitre wrote:

> On Mon, 23 Feb 2015, Peter Zijlstra wrote:
> > The reported function that fails: bL_switcher_restore_cpus() is called
> > in the error paths of the former and the main path in the latter to make
> > the 'stolen' cpus re-appear.
> >
> > The patch in question somehow makes that go boom.
> >
> >
> > Now what all do you need to do to make it go boom? Just enable/disable
> > the switcher once and it'll explode? Or does it need to do actual
> > switches while it is enabled?
> It gets automatically enabled during boot. Then several switches are
> performed while user space is brought up. If I manually disable it
> via /sys then it goes boom.

OK. Forget the bL switcher. I configured it out of my kernel and then
managed to get the same crash by simply hotplugging out one CPU and
plugging it back in.

$ echo 0 > /sys/devices/system/cpu/cpu2/online
[CPU2 gone]
$ echo 1 > /sys/devices/system/cpu/cpu2/online

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