powerpc/ppc64: Use preempt_schedule_irq instead of preempt_schedule

Based on an original patch by Valentine Barshak <vbarshak@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.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index f9fd54b..9763267 100644 (file)
--- 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