[POWERPC] Fix loop logic in irq_alloc_virt()

There's a bug in irq_alloc_virt() if it's asked for more than 1 interrupt,
if it can't find a slot it might look past the end of the irq_map.
To be clear: the bug is that the continue affects the inner for loop,
not the outer one, so i becomes j + 1 and then we continue the inner
loop without checking if i is still <= limit.

This fixes it. No one in the kernel actually calls this with count >
1, so it's not critical.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 10 insertions, 9 deletions

diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index b4432332341f..c3f58f2f9f52 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -777,7 +777,6 @@ unsigned int irq_alloc_virt(struct irq_host *host,
 {
         unsigned long flags;
         unsigned int i, j, found = NO_IRQ;
-        unsigned int limit = irq_virq_count - count;
 
         if (count == 0 || count > (irq_virq_count - NUM_ISA_INTERRUPTS))
                 return NO_IRQ;
@@ -794,14 +793,16 @@ unsigned int irq_alloc_virt(struct irq_host *host,
         /* Look for count consecutive numbers in the allocatable
          * (non-legacy) space
          */
-        for (i = NUM_ISA_INTERRUPTS; i <= limit; ) {
-                for (j = i; j < (i + count); j++)
-                        if (irq_map[j].host != NULL) {
-                                i = j + 1;
-                                continue;
-                        }
-                found = i;
-                break;
+        for (i = NUM_ISA_INTERRUPTS, j = 0; i < irq_virq_count; i++) {
+                if (irq_map[i].host != NULL)
+                        j = 0;
+                else
+                        j++;
+
+                if (j == count) {
+                        found = i - count + 1;
+                        break;
+                }
         }
         if (found == NO_IRQ) {
                 spin_unlock_irqrestore(&irq_big_lock, flags);