[patch 28/30] xen/events: Reduce irq_info::spurious_cnt storage size

[Thomas Gleixner]

To prepare for interrupt spreading reduce the storage size of
irq_info::spurious_cnt to u8 so the required flag for the spreading logic
will not increase the storage size.

Protect the usage site against overruns.

Signed-off-by: Thomas Gleixner <t...@linutronix.de>
Cc: Boris Ostrovsky <boris.ostrov...@oracle.com>
Cc: Juergen Gross <jgr...@suse.com>
Cc: Stefano Stabellini <sstabell...@kernel.org>
Cc: xen-de...@lists.xenproject.org
---
 drivers/xen/events/events_base.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -95,7 +95,7 @@ struct irq_info {
        struct list_head list;
        struct list_head eoi_list;
        short refcnt;
-       short spurious_cnt;
+       u8 spurious_cnt;
        enum xen_irq_type type; /* type */
        unsigned irq;
        evtchn_port_t evtchn;   /* event channel */
@@ -528,8 +528,10 @@ static void xen_irq_lateeoi_locked(struc
                return;
 
        if (spurious) {
-               if ((1 << info->spurious_cnt) < (HZ << 2))
-                       info->spurious_cnt++;
+               if ((1 << info->spurious_cnt) < (HZ << 2)) {
+                       if (info->spurious_cnt != 0xFF)
+                               info->spurious_cnt++;
+               }
                if (info->spurious_cnt > 1) {
                        delay = 1 << (info->spurious_cnt - 2);
                        if (delay > HZ)