3.6.7-rt18: kernel BUG at .../kernel/sched/core.c:3817!
Grant reported this same problem for 3.6.5-rt15.
I am seeing it on a different arm board.
Here is the BUG_ON():
asmlinkage void __sched preempt_schedule_irq(void)
{
struct thread_info *ti = current_thread_info();
/* Catch callers which need to be fixed */
BUG_ON(ti->preempt_count || !irqs_disabled());
Putting in some extra printk(), the BUG_ON() is triggering because
ti->preempt_count is non-zero.
It appears that the cause is in arch/arm/kernel/entry-armv.S.
The call to preempt_schedule_irq() is from svc_preempt:
#ifdef CONFIG_PREEMPT
svc_preempt:
mov r8, lr
1: bl preempt_schedule_irq @ irq en/disable is done
inside
svc_preempt is branched to from one of two possible places. The first was
present before the lazy preempt code was added. The first appears ok to me.
(Note that the first branch does not occur if preempt count is non-zero.)
The second branch can occur even if the preempt count is non-zero (which is
what the BUG_ON() is finding):
__irq_svc:
svc_entry
irq_handler
#ifdef CONFIG_PREEMPT
get_thread_info tsk
ldr r8, [tsk, #TI_PREEMPT] @ get preempt count
ldr r0, [tsk, #TI_FLAGS] @ get flags
teq r8, #0 @ if preempt count != 0
movne r0, #0 @ force flags to 0
tst r0, #_TIF_NEED_RESCHED
blne svc_preempt
ldr r8, [tsk, #TI_PREEMPT_LAZY] @ get preempt lazy count
ldr r0, [tsk, #TI_FLAGS] @ get flags
teq r8, #0 @ if preempt lazy count != 0
movne r0, #0 @ force flags to 0
tst r0, #_TIF_NEED_RESCHED_LAZY
blne svc_preempt
#endif
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