genirq: Use IRQ_BITMAP_BITS as search size in irq_alloc_descs()

The runtime expansion of nr_irqs does not take into account that
bitmap_find_next_zero_area() returns "start" + size in case the search
for an matching zero area fails. That results in a start value which
can be completely off and is not covered by the following
expand_nr_irqs() and possibly outside of the absolute limit. But we
use it without further checking.

Use IRQ_BITMAP_BITS as the limit for the bitmap search and expand
nr_irqs when the start bit is beyond nr_irqs. So start is always
pointing to the correct area in the bitmap. nr_irqs is just the limit
for irq enumerations, not the real limit for the irq space.

[ tglx: Let irq_expand_nr_irqs() take the new upper end so we do not
  	expand nr_irqs more than necessary. Made changelog readable ]

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <4D6014F9.8040605@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 8 insertions, 7 deletions

diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
index 394ab6a6c62..dbccc799407 100644
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -207,11 +207,11 @@ struct irq_desc * __ref irq_to_desc_alloc_node(unsigned int irq, int node)
         return NULL;
 }
 
-static int irq_expand_nr_irqs(unsigned int cnt)
+static int irq_expand_nr_irqs(unsigned int nr)
 {
-        if (nr_irqs + cnt > IRQ_BITMAP_BITS)
+        if (nr > IRQ_BITMAP_BITS)
                 return -ENOMEM;
-        nr_irqs += cnt;
+        nr_irqs = nr;
         return 0;
 }
 
@@ -298,7 +298,7 @@ static inline int alloc_descs(unsigned int start, unsigned int cnt, int node)
         return start;
 }
 
-static int irq_expand_nr_irqs(unsigned int cnt)
+static int irq_expand_nr_irqs(unsigned int nr)
 {
         return -ENOMEM;
 }
@@ -346,13 +346,14 @@ irq_alloc_descs(int irq, unsigned int from, unsigned int cnt, int node)
 
         mutex_lock(&sparse_irq_lock);
 
-        start = bitmap_find_next_zero_area(allocated_irqs, nr_irqs, from, cnt, 0);
+        start = bitmap_find_next_zero_area(allocated_irqs, IRQ_BITMAP_BITS,
+                                           from, cnt, 0);
         ret = -EEXIST;
         if (irq >=0 && start != irq)
                 goto err;
 
-        if (start >= nr_irqs) {
-                ret = irq_expand_nr_irqs(cnt);
+        if (start + cnt > nr_irqs) {
+                ret = irq_expand_nr_irqs(start + cnt);
                 if (ret)
                         goto err;
         }