md: Fix is_mddev_idle test (again).

There are two problems with is_mddev_idle.

1/ sync_io is 'atomic_t' and hence 'int'.  curr_events and all the
   rest are 'long'.
   So if sync_io were to wrap on a 64bit host, the value of
   curr_events would go very negative suddenly, and take a very
   long time to return to positive.

   So do all calculations as 'int'.  That gives us plenty of precision
   for what we need.

2/ To initialise rdev->last_events we simply call is_mddev_idle, on
   the assumption that it will make sure that last_events is in a
   suitable range.  It used to do this, but now it does not.
   So now we need to be more explicit about initialisation.

Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 8 insertions, 8 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 03b4cd0a6344..a99c50e217c0 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -5716,19 +5716,19 @@ int unregister_md_personality(struct mdk_personality *p)
         return 0;
 }
 
-static int is_mddev_idle(mddev_t *mddev)
+static int is_mddev_idle(mddev_t *mddev, int init)
 {
         mdk_rdev_t * rdev;
         int idle;
-        long curr_events;
+        int curr_events;
 
         idle = 1;
         rcu_read_lock();
         rdev_for_each_rcu(rdev, mddev) {
                 struct gendisk *disk = rdev->bdev->bd_contains->bd_disk;
-                curr_events = part_stat_read(&disk->part0, sectors[0]) +
-                                part_stat_read(&disk->part0, sectors[1]) -
-                                atomic_read(&disk->sync_io);
+                curr_events = (int)part_stat_read(&disk->part0, sectors[0]) +
+                              (int)part_stat_read(&disk->part0, sectors[1]) -
+                              atomic_read(&disk->sync_io);
                 /* sync IO will cause sync_io to increase before the disk_stats
                  * as sync_io is counted when a request starts, and
                  * disk_stats is counted when it completes.
@@ -5751,7 +5751,7 @@ static int is_mddev_idle(mddev_t *mddev)
                  * always make curr_events less than last_events.
                  *
                  */
-                if (curr_events - rdev->last_events > 4096) {
+                if (init || curr_events - rdev->last_events > 64) {
                         rdev->last_events = curr_events;
                         idle = 0;
                 }
@@ -5994,7 +5994,7 @@ void md_do_sync(mddev_t *mddev)
                "(but not more than %d KB/sec) for %s.\n",
                speed_max(mddev), desc);
 
-        is_mddev_idle(mddev); /* this also initializes IO event counters */
+        is_mddev_idle(mddev, 1); /* this initializes IO event counters */
 
         io_sectors = 0;
         for (m = 0; m < SYNC_MARKS; m++) {
@@ -6096,7 +6096,7 @@ void md_do_sync(mddev_t *mddev)
 
                 if (currspeed > speed_min(mddev)) {
                         if ((currspeed > speed_max(mddev)) ||
-                                        !is_mddev_idle(mddev)) {
+                                        !is_mddev_idle(mddev, 0)) {
                                 msleep(500);
                                 goto repeat;
                         }