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SubjectRe: ftrace: preemptoff selftest not working

* Steven Rostedt <rostedt@goodmis.org> wrote:

>
> On Tue, 18 Nov 2008, Ingo Molnar wrote:
> >
> > * Steven Rostedt <rostedt@goodmis.org> wrote:
> >
> > > > Hence the trace buffer will be empty. The patch below makes the
> > > > selftests working for me, since then they run in preemptible
> > > > context. But it is ugly and I'm not proposing it for upstream ;)
> > > >
> > > > Just wanted to make you aware that there is a bug.
> > >
> > > Yep, this might be a better answer than what I put into linux-tip
> > > (and my git repo).
> > >
> > > See:
> > >
> > > ftrace: force pass of preemptoff selftest
> > >
> > > The cause of the bug was the conversion of the BKL back to a
> > > spinlock, and making it non preempt. The initcall code is called
> > > with the BKL applied which now means it can not preempt. This breaks
> > > the preempt tracer selftest.
> > >
> > > My solution was to just force a pass if this is detected. Perhaps
> > > moving the test might be better.
> >
> > it would be better to just drop the BKL in that selftest. (or in all
> > selftests - an elevated preempt count will skew a number of things)
>
> I have no problem with that, but does the BKL play any role for
> being held? I have no idea why it is taken in boot up, so I'm
> hestiant to touch it.

we can drop it in selected initcalls just fine. Its only role is
old-style init functions racing with other async contexts of
themselves.

Ingo


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