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>

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 03b4cd0..a99c50e 100644 (file)
--- 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;
                        }

diff --git a/include/linux/raid/md_k.h b/include/linux/raid/md_k.h
index 9743e4d..4aedb9f 100644 (file)
--- a/include/linux/raid/md_k.h
+++ b/include/linux/raid/md_k.h
@@ -51,7 +51,7 @@ struct mdk_rdev_s
 
        sector_t size;                  /* Device size (in blocks) */
        mddev_t *mddev;                 /* RAID array if running */
-       long last_events;               /* IO event timestamp */
+       int last_events;                /* IO event timestamp */
 
        struct block_device *bdev;      /* block device handle */