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>

1 files changed, 21 insertions, 20 deletions

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index f9fd54bfcc84..9763267e38b4 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