Re: ftrace: preemptoff selftest not working

[Ingo Molnar]

* Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> 
> On Tue, 18 Nov 2008, Ingo Molnar wrote:
> > 
> > * Steven Rostedt <rostedt@xxxxxxxxxxx> 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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