> So I _think_ that the irqs on/off accounting for lockdep isn't quite
> right. What do you think of this slightly modified version ? I've only
> done a quick boot test on a G5 with lockdep enabled and a played a bit,
> nothing shows up so far but it's definitely not conclusive.
>
> The main difference is that I call trace_hardirqs_off to "advertise"
> the fact that we are soft-disabling (it could be a dup, but at this
> stage this is no big deal, but it's not always, like in syscall return
> the kernel thinks we have interrupts enabled and could thus get out
> of sync without that).
>
> I also mark the PACA hard disable to reflect the MSR:EE state before
> calling into preempt_schedule_irq().
Allright, second thought :-)
It's probably simpler to just keep hardirqs off. Code is smaller and
simpler and the scheduler will re-enable them soon enough anyways.
This version of the patch also spaces the code a bit and adds comments
which makes them (the code and the patch) more readable.
Cheers,
Ben.
From: Benjamin Herrenschmidt <b...@kernel.crashing.org>
[PATCH v3] powerpc/ppc64: Use preempt_schedule_irq instead of preempt_schedule
Based on an original patch by Valentine Barshak <vbars...@ru.mvista.com>
Use preempt_schedule_irq to prevent infinite irq-entry and
eventual stack overflow problems with fast-paced IRQ sources.
This kind of problems has been observed on the PASemi Electra IDE
controller. We have to make sure we are soft-disabled before calling
preempt_schedule_irq and hard disable interrupts after that
to avoid unrecoverable exceptions.
This patch also moves the "clrrdi r9,r1,THREAD_SHIFT" out of
the #ifdef CONFIG_PPC_BOOK3E scope, since r9 is clobbered
and has to be restored in both cases.
---
arch/powerpc/kernel/entry_64.S | 41 ++++++++++++++++++++-------------------
1 files changed, 21 insertions(+), 20 deletions(-)
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index f9fd54b..9763267 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -658,42 +658,43 @@ do_work:
cmpdi r0,0
crandc eq,cr1*4+eq,eq
bne restore
- /* here we are preempting the current task */
-1:
-#ifdef CONFIG_TRACE_IRQFLAGS
- bl .trace_hardirqs_on
- /* Note: we just clobbered r10 which used to contain the previous
- * MSR before the hard-disabling done by the caller of do_work.
- * We don't have that value anymore, but it doesn't matter as
- * we will hard-enable unconditionally, we can just reload the
- * current MSR into r10
+
+ /* Here we are preempting the current task.
+ *
+ * Ensure interrupts are soft-disabled. We also properly mark
+ * the PACA to reflect the fact that they are hard-disabled
+ * and trace the change
*/
- mfmsr r10
-#endif /* CONFIG_TRACE_IRQFLAGS */
- li r0,1
+ li r0,0
stb r0,PACASOFTIRQEN(r13)
stb r0,PACAHARDIRQEN(r13)
+ TRACE_DISABLE_INTS
+
+ /* Call the scheduler with soft IRQs off */
+1: bl .preempt_schedule_irq
+
+ /* Hard-disable interrupts again (and update PACA) */
#ifdef CONFIG_PPC_BOOK3E
- wrteei 1
- bl .preempt_schedule
wrteei 0
#else
- ori r10,r10,MSR_EE
- mtmsrd r10,1 /* reenable interrupts */
- bl .preempt_schedule
mfmsr r10
- clrrdi r9,r1,THREAD_SHIFT
- rldicl r10,r10,48,1 /* disable interrupts again */
+ rldicl r10,r10,48,1
rotldi r10,r10,16
mtmsrd r10,1
#endif /* CONFIG_PPC_BOOK3E */
+ li r0,0
+ stb r0,PACAHARDIRQEN(r13)
+
+ /* Re-test flags and eventually loop */
+ clrrdi r9,r1,THREAD_SHIFT
ld r4,TI_FLAGS(r9)
andi. r0,r4,_TIF_NEED_RESCHED
bne 1b
b restore
user_work:
-#endif
+#endif /* CONFIG_PREEMPT */
+
/* Enable interrupts */
#ifdef CONFIG_PPC_BOOK3E
wrteei 1
--
1.6.1.2.14.gf26b5
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