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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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