md: allow a maximum extent to be set for resyncing

This allows userspace to control resync/reshape progress and synchronise it
with other activities, such as shared access in a SAN, or backing up critical
sections during a tricky reshape.

Writing a number of sectors (which must be a multiple of the chunk size if
such is meaningful) causes a resync to pause when it gets to that point.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

6 files changed, 107 insertions, 10 deletions

diff --git a/Documentation/md.txt b/Documentation/md.txt
index 5818628207b5..396cdd982c26 100644
--- a/Documentation/md.txt
+++ b/Documentation/md.txt
@@ -416,6 +416,16 @@ also have
      sectors in total that could need to be processed.  The two
      numbers are separated by a '/'  thus effectively showing one
      value, a fraction of the process that is complete.
+     A 'select' on this attribute will return when resync completes,
+     when it reaches the current sync_max (below) and possibly at
+     other times.
+
+   sync_max
+     This is a number of sectors at which point a resync/recovery
+     process will pause.  When a resync is active, the value can
+     only ever be increased, never decreased.  The value of 'max'
+     effectively disables the limit.
+
 
    sync_speed
      This shows the current actual speed, in K/sec, of the current
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 00788c56276f..79eb63fdb4b3 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -275,6 +275,7 @@ static mddev_t * mddev_find(dev_t unit)
         spin_lock_init(&new->write_lock);
         init_waitqueue_head(&new->sb_wait);
         new->reshape_position = MaxSector;
+        new->resync_max = MaxSector;
 
         new->queue = blk_alloc_queue(GFP_KERNEL);
         if (!new->queue) {
@@ -2921,6 +2922,43 @@ sync_completed_show(mddev_t *mddev, char *page)
 static struct md_sysfs_entry md_sync_completed = __ATTR_RO(sync_completed);
 
 static ssize_t
+max_sync_show(mddev_t *mddev, char *page)
+{
+        if (mddev->resync_max == MaxSector)
+                return sprintf(page, "max\n");
+        else
+                return sprintf(page, "%llu\n",
+                               (unsigned long long)mddev->resync_max);
+}
+static ssize_t
+max_sync_store(mddev_t *mddev, const char *buf, size_t len)
+{
+        if (strncmp(buf, "max", 3) == 0)
+                mddev->resync_max = MaxSector;
+        else {
+                char *ep;
+                unsigned long long max = simple_strtoull(buf, &ep, 10);
+                if (ep == buf || (*ep != 0 && *ep != '\n'))
+                        return -EINVAL;
+                if (max < mddev->resync_max &&
+                    test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
+                        return -EBUSY;
+
+                /* Must be a multiple of chunk_size */
+                if (mddev->chunk_size) {
+                        if (max & (sector_t)((mddev->chunk_size>>9)-1))
+                                return -EINVAL;
+                }
+                mddev->resync_max = max;
+        }
+        wake_up(&mddev->recovery_wait);
+        return len;
+}
+
+static struct md_sysfs_entry md_max_sync =
+__ATTR(sync_max, S_IRUGO|S_IWUSR, max_sync_show, max_sync_store);
+
+static ssize_t
 suspend_lo_show(mddev_t *mddev, char *page)
 {
         return sprintf(page, "%llu\n", (unsigned long long)mddev->suspend_lo);
@@ -3030,6 +3068,7 @@ static struct attribute *md_redundancy_attrs[] = {
         &md_sync_max.attr,
         &md_sync_speed.attr,
         &md_sync_completed.attr,
+        &md_max_sync.attr,
         &md_suspend_lo.attr,
         &md_suspend_hi.attr,
         &md_bitmap.attr,
@@ -3579,6 +3618,7 @@ static int do_md_stop(mddev_t * mddev, int mode)
                 mddev->size = 0;
                 mddev->raid_disks = 0;
                 mddev->recovery_cp = 0;
+                mddev->resync_max = MaxSector;
                 mddev->reshape_position = MaxSector;
                 mddev->external = 0;
 
@@ -5443,8 +5483,16 @@ void md_do_sync(mddev_t *mddev)
                 sector_t sectors;
 
                 skipped = 0;
+                if (j >= mddev->resync_max) {
+                        sysfs_notify(&mddev->kobj, NULL, "sync_completed");
+                        wait_event(mddev->recovery_wait,
+                                   mddev->resync_max > j
+                                   || kthread_should_stop());
+                }
+                if (kthread_should_stop())
+                        goto interrupted;
                 sectors = mddev->pers->sync_request(mddev, j, &skipped,
-                                            currspeed < speed_min(mddev));
+                                                  currspeed < speed_min(mddev));
                 if (sectors == 0) {
                         set_bit(MD_RECOVERY_ERR, &mddev->recovery);
                         goto out;
@@ -5486,15 +5534,9 @@ void md_do_sync(mddev_t *mddev)
                 }
 
 
-                if (kthread_should_stop()) {
-                        /*
-                         * got a signal, exit.
-                         */
-                        printk(KERN_INFO 
-                                "md: md_do_sync() got signal ... exiting\n");
-                        set_bit(MD_RECOVERY_INTR, &mddev->recovery);
-                        goto out;
-                }
+                if (kthread_should_stop())
+                        goto interrupted;
+
 
                 /*
                  * this loop exits only if either when we are slower than
@@ -5558,9 +5600,22 @@ void md_do_sync(mddev_t *mddev)
 
  skip:
         mddev->curr_resync = 0;
+        mddev->resync_max = MaxSector;
+        sysfs_notify(&mddev->kobj, NULL, "sync_completed");
         wake_up(&resync_wait);
         set_bit(MD_RECOVERY_DONE, &mddev->recovery);
         md_wakeup_thread(mddev->thread);
+        return;
+
+ interrupted:
+        /*
+         * got a signal, exit.
+         */
+        printk(KERN_INFO
+               "md: md_do_sync() got signal ... exiting\n");
+        set_bit(MD_RECOVERY_INTR, &mddev->recovery);
+        goto out;
+
 }
 EXPORT_SYMBOL_GPL(md_do_sync);
 
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index e0b8d0dd7a87..ae7c15207df5 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -1767,6 +1767,8 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
                 return rv;
         }
 
+        if (max_sector > mddev->resync_max)
+                max_sector = mddev->resync_max; /* Don't do IO beyond here */
         nr_sectors = 0;
         sync_blocks = 0;
         do {
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index ba125277c6c4..d6f12882424d 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1657,6 +1657,9 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
                 return (max_sector - sector_nr) + sectors_skipped;
         }
 
+        if (max_sector > mddev->resync_max)
+                max_sector = mddev->resync_max; /* Don't do IO beyond here */
+
         /* make sure whole request will fit in a chunk - if chunks
          * are meaningful
          */
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 388a974d63ef..e946de6f46bc 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3698,6 +3698,25 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped
                 release_stripe(sh);
                 first_sector += STRIPE_SECTORS;
         }
+        /* If this takes us to the resync_max point where we have to pause,
+         * then we need to write out the superblock.
+         */
+        sector_nr += conf->chunk_size>>9;
+        if (sector_nr >= mddev->resync_max) {
+                /* Cannot proceed until we've updated the superblock... */
+                wait_event(conf->wait_for_overlap,
+                           atomic_read(&conf->reshape_stripes) == 0);
+                mddev->reshape_position = conf->expand_progress;
+                set_bit(MD_CHANGE_DEVS, &mddev->flags);
+                md_wakeup_thread(mddev->thread);
+                wait_event(mddev->sb_wait,
+                           !test_bit(MD_CHANGE_DEVS, &mddev->flags)
+                           || kthread_should_stop());
+                spin_lock_irq(&conf->device_lock);
+                conf->expand_lo = mddev->reshape_position;
+                spin_unlock_irq(&conf->device_lock);
+                wake_up(&conf->wait_for_overlap);
+        }
         return conf->chunk_size>>9;
 }
 
@@ -3734,6 +3753,12 @@ static inline sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *ski
         if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
                 return reshape_request(mddev, sector_nr, skipped);
 
+        /* No need to check resync_max as we never do more than one
+         * stripe, and as resync_max will always be on a chunk boundary,
+         * if the check in md_do_sync didn't fire, there is no chance
+         * of overstepping resync_max here
+         */
+
         /* if there is too many failed drives and we are trying
          * to resync, then assert that we are finished, because there is
          * nothing we can do.
diff --git a/include/linux/raid/md_k.h b/include/linux/raid/md_k.h
index b579cc628303..c77dca3221ed 100644
--- a/include/linux/raid/md_k.h
+++ b/include/linux/raid/md_k.h
@@ -219,6 +219,8 @@ struct mddev_s
         atomic_t                        recovery_active; /* blocks scheduled, but not written */
         wait_queue_head_t               recovery_wait;
         sector_t                        recovery_cp;
+        sector_t                        resync_max;     /* resync should pause
+                                                         * when it gets here */
 
         spinlock_t                      write_lock;
         wait_queue_head_t               sb_wait;        /* for waiting on superblock updates */