Unset LOCKDEP and TRACE_IRQFLAGS_SUPPORT

[gilles.chanteperdrix@xenomai.org (Gilles Chanteperdrix)]

On Fri, Oct 02, 2015 at 09:56:39AM -0600, Jim Cromie wrote:
> On Sun, Sep 27, 2015 at 8:52 AM, <Valdis.Kletnieks@vt.edu> wrote:
> 
> > On Sun, 27 Sep 2015 15:08:57 +1300, vibnwis said:
> >
> > > Xenomai patching succeeded but when running one of is test apps,
> > "latency"
> > > showing
> > > > > > > > > >> > 0"000.000| BUG in low_init(): [main] mlockall: Cannot
> > > allocate
> > > > > > > memory
> > > And the mailing list member suggested the following
> >
> > Is that in dmesg, or output from the test program?
> > Is there more output, or is that it?
> >
> > Personally, if TRACE_IRQFLAGS is causing an issue with mlock, I'd suspect
> > a very buggy patch indeed.  If it can't tolerate a trace function being
> > turned on, there;s probably some very questionable coding in there.....
> >
> >
> 
> FWIW, I think Xenomai is far better smelling than your quick sniff has told
> your olfactory sensors

TRACE_IRQFLAGS is broken with the I-pipe patch. At least on ARM. The
visible result is LOCKDEP false positives, but there may be some
more subtle kernel data structures corruption due to the fact that
the TRACE_IRQFLAFGS code is called from the Xenomai context. The
principle of Xenomai is to be able to run while Linux believes
its interrupts are off, in the middle of its critical sections. For
this to be possible, the code run in this context must never touch
any Linux kernel data structures. Enabling TRACE_IRQFLAGS breaks
this assumption: Linux code which potentially accesses Linux data
structures gets called from the Xenomai context. The consequences
can be anything, such as mlock failing, though in practice we never
get any report about that. The usual reason for mlockall failing is
because the user is not root, and with default ulimit settings at
least, mlockall can not be called by non-root users.

Anyway, the reason why TRACE_IRQFLAGS is still broken is my fault:
Jan has sent patches months ago, which I did not check.

-- 
					    Gilles.
https://click-hack.org