powerpc/irq: Fix another case of lazy IRQ state getting out of sync

So we have another case of paca->irq_happened getting out of
sync with the HW irq state. This can happen when a perfmon
interrupt occurs while soft disabled, as it will return to a
soft disabled but hard enabled context while leaving a stale
PACA_IRQ_HARD_DIS flag set.

This patch fixes it, and also adds a test for the condition
of those flags being out of sync in arch_local_irq_restore()
when CONFIG_TRACE_IRQFLAGS is enabled.

This helps catching those gremlins faster (and so far I
can't seem see any anymore, so that's good news).

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

2 files changed, 44 insertions, 13 deletions

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index fc6015027a86..ef2074c3e906 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -588,23 +588,19 @@ _GLOBAL(ret_from_except_lite)
 fast_exc_return_irq:
 restore:
         /*
-         * This is the main kernel exit path, we first check if we
-         * have to change our interrupt state.
+         * This is the main kernel exit path. First we check if we
+         * are about to re-enable interrupts
          */
         ld      r5,SOFTE(r1)
         lbz     r6,PACASOFTIRQEN(r13)
-        cmpwi   cr1,r5,0
-        cmpw    cr0,r5,r6
-        beq     cr0,4f
+        cmpwi   cr0,r5,0
+        beq     restore_irq_off
 
-        /* We do, handle disable first, which is easy */
-        bne     cr1,3f;
-        li      r0,0
-        stb     r0,PACASOFTIRQEN(r13);
-        TRACE_DISABLE_INTS
-        b       4f
+        /* We are enabling, were we already enabled ? Yes, just return */
+        cmpwi   cr0,r6,1
+        beq     cr0,do_restore
 
-3:      /*
+        /*
          * We are about to soft-enable interrupts (we are hard disabled
          * at this point). We check if there's anything that needs to
          * be replayed first.
@@ -626,7 +622,7 @@ restore_no_replay:
         /*
          * Final return path. BookE is handled in a different file
          */
-4:
+do_restore:
 #ifdef CONFIG_PPC_BOOK3E
         b       .exception_return_book3e
 #else
@@ -700,6 +696,25 @@ fast_exception_return:
 #endif /* CONFIG_PPC_BOOK3E */
 
         /*
+         * We are returning to a context with interrupts soft disabled.
+         *
+         * However, we may also about to hard enable, so we need to
+         * make sure that in this case, we also clear PACA_IRQ_HARD_DIS
+         * or that bit can get out of sync and bad things will happen
+         */
+restore_irq_off:
+        ld      r3,_MSR(r1)
+        lbz     r7,PACAIRQHAPPENED(r13)
+        andi.   r0,r3,MSR_EE
+        beq     1f
+        rlwinm  r7,r7,0,~PACA_IRQ_HARD_DIS
+        stb     r7,PACAIRQHAPPENED(r13)
+1:      li      r0,0
+        stb     r0,PACASOFTIRQEN(r13);
+        TRACE_DISABLE_INTS
+        b       do_restore
+
+        /*
          * Something did happen, check if a re-emit is needed
          * (this also clears paca->irq_happened)
          */
@@ -748,6 +763,9 @@ restore_check_irq_replay:
 #endif /* CONFIG_PPC_BOOK3E */
 1:      b       .ret_from_except /* What else to do here ? */
  
+
+
+3:
 do_work:
 #ifdef CONFIG_PREEMPT
         andi.   r0,r3,MSR_PR    /* Returning to user mode? */
diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index c6c6f3b7f8cd..641da9e868ce 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -229,6 +229,19 @@ notrace void arch_local_irq_restore(unsigned long en)
          */
         if (unlikely(irq_happened != PACA_IRQ_HARD_DIS))
                 __hard_irq_disable();
+#ifdef CONFIG_TRACE_IRQFLAG
+        else {
+                /*
+                 * We should already be hard disabled here. We had bugs
+                 * where that wasn't the case so let's dbl check it and
+                 * warn if we are wrong. Only do that when IRQ tracing
+                 * is enabled as mfmsr() can be costly.
+                 */
+                if (WARN_ON(mfmsr() & MSR_EE))
+                        __hard_irq_disable();
+        }
+#endif /* CONFIG_TRACE_IRQFLAG */
+
         set_soft_enabled(0);
 
         /*