1 files changed, 38 insertions, 7 deletions

diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index 7e65bad522cb..ac89a5deaca2 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -238,15 +238,47 @@ static struct page *read_sb_page(mddev_t *mddev, long offset, unsigned long inde
 
 }
 
+static mdk_rdev_t *next_active_rdev(mdk_rdev_t *rdev, mddev_t *mddev)
+{
+        /* Iterate the disks of an mddev, using rcu to protect access to the
+         * linked list, and raising the refcount of devices we return to ensure
+         * they don't disappear while in use.
+         * As devices are only added or removed when raid_disk is < 0 and
+         * nr_pending is 0 and In_sync is clear, the entries we return will
+         * still be in the same position on the list when we re-enter
+         * list_for_each_continue_rcu.
+         */
+        struct list_head *pos;
+        rcu_read_lock();
+        if (rdev == NULL)
+                /* start at the beginning */
+                pos = &mddev->disks;
+        else {
+                /* release the previous rdev and start from there. */
+                rdev_dec_pending(rdev, mddev);
+                pos = &rdev->same_set;
+        }
+        list_for_each_continue_rcu(pos, &mddev->disks) {
+                rdev = list_entry(pos, mdk_rdev_t, same_set);
+                if (rdev->raid_disk >= 0 &&
+                    test_bit(In_sync, &rdev->flags) &&
+                    !test_bit(Faulty, &rdev->flags)) {
+                        /* this is a usable devices */
+                        atomic_inc(&rdev->nr_pending);
+                        rcu_read_unlock();
+                        return rdev;
+                }
+        }
+        rcu_read_unlock();
+        return NULL;
+}
+
 static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
 {
-        mdk_rdev_t *rdev;
+        mdk_rdev_t *rdev = NULL;
         mddev_t *mddev = bitmap->mddev;
 
-        rcu_read_lock();
-        rdev_for_each_rcu(rdev, mddev)
-                if (test_bit(In_sync, &rdev->flags)
-                    && !test_bit(Faulty, &rdev->flags)) {
+        while ((rdev = next_active_rdev(rdev, mddev)) != NULL) {
                         int size = PAGE_SIZE;
                         if (page->index == bitmap->file_pages-1)
                                 size = roundup(bitmap->last_page_size,
@@ -281,8 +313,7 @@ static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
                                        + page->index * (PAGE_SIZE/512),
                                        size,
                                        page);
-                }
-        rcu_read_unlock();
+        }
 
         if (wait)
                 md_super_wait(mddev);