From mboxrd@z Thu Jan  1 00:00:00 1970
From: Rolf Peukert <rolf.peukert@imms.de>
Subject: 3.2.60-rt87: arm: Doesn't boot in certain case
Date: Thu, 19 Jun 2014 21:04:06 +0200
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References: <20140618201355.3f8baecb@gandalf.local.home>
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Cc: Steven Rostedt <rostedt@goodmis.org>
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Hello Steven,

I just tried the new kernel version 3.2.60-rt87 on our ARM-Cortex-A8
board and while it works fine with the standard configuration, it won't
boot if the option CONFIG_MISSED_TIMER_OFFSETS_HIST is set.

The kernel error message reports a NULL pointer dereference at
__hrtimer_start_range_ns+0xf4, which probably is line 1038 in file
kernel/hrtimer.c, where new_base->get_time() is called before new_base
is set.
(actually there was a compiler warning too, but I didn't pay enough
attention to the compiler output...)


#ifdef CONFIG_MISSED_TIMER_OFFSETS_HIST
        {
                ktime_t now = new_base->get_time();

                if (ktime_to_ns(tim) < ktime_to_ns(now))
                        timer->praecox = now;
                else
                        timer->praecox = ktime_set(0, 0);
        }
#endif
        hrtimer_set_expires_range_ns(timer, tim, delta_ns);

        /* Switch the timer base, if necessary: */
        new_base = switch_hrtimer_base(timer, base, mode &
HRTIMER_MODE_PINNED);


Since I moved the #ifdef...#endif block down below the
new_base=switch_hrtimer... statement, the kernel boots and works so far,
but I'm not sure if this is what was originally intended here.

Best regards
Rolf