writeback: splice dirty inode entries to default bdi on bdi_destroy()

We cannot safely ensure that the inodes are all gone at this point
in time, and we must not destroy this bdi with inodes having off it.
So just splice our entries to the default bdi since that one will
always persist.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 13 insertions, 1 deletions

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index fd93566345b6..3d3accb1f800 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -668,7 +668,19 @@ void bdi_destroy(struct backing_dev_info *bdi)
 {
         int i;
 
-        WARN_ON(bdi_has_dirty_io(bdi));
+        /*
+         * Splice our entries to the default_backing_dev_info, if this
+         * bdi disappears
+         */
+        if (bdi_has_dirty_io(bdi)) {
+                struct bdi_writeback *dst = &default_backing_dev_info.wb;
+
+                spin_lock(&inode_lock);
+                list_splice(&bdi->wb.b_dirty, &dst->b_dirty);
+                list_splice(&bdi->wb.b_io, &dst->b_io);
+                list_splice(&bdi->wb.b_more_io, &dst->b_more_io);
+                spin_unlock(&inode_lock);
+        }
 
         bdi_unregister(bdi);