bdi: reimplement bdev_inode_switch_bdi()

A block_device may be attached to different gendisks and thus
different bdis over time.  bdev_inode_switch_bdi() is used to switch
the associated bdi.  The function assumes that the inode could be
dirty and transfers it between bdis if so.  This is a bit nasty in
that it reaches into bdi internals.

This patch reimplements the function so that it writes out the inode
if dirty.  This is a lot simpler and can be implemented without
exposing bdi internals.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 11 insertions, 21 deletions

diff --git a/fs/block_dev.c b/fs/block_dev.c
index d3251eca6429..cc8d68ac29aa 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -50,32 +50,22 @@ inline struct block_device *I_BDEV(struct inode *inode)
 EXPORT_SYMBOL(I_BDEV);
 
 /*
- * Move the inode from its current bdi to a new bdi. If the inode is dirty we
- * need to move it onto the dirty list of @dst so that the inode is always on
- * the right list.
+ * Move the inode from its current bdi to a new bdi.  Make sure the inode
+ * is clean before moving so that it doesn't linger on the old bdi.
  */
 static void bdev_inode_switch_bdi(struct inode *inode,
                         struct backing_dev_info *dst)
 {
-        struct backing_dev_info *old = inode->i_data.backing_dev_info;
-        bool wakeup_bdi = false;
-
-        if (unlikely(dst == old))               /* deadlock avoidance */
-                return;
-        bdi_lock_two(&old->wb, &dst->wb);
-        spin_lock(&inode->i_lock);
-        inode->i_data.backing_dev_info = dst;
-        if (inode->i_state & I_DIRTY) {
-                if (bdi_cap_writeback_dirty(dst) && !wb_has_dirty_io(&dst->wb))
-                        wakeup_bdi = true;
-                list_move(&inode->i_wb_list, &dst->wb.b_dirty);
+        while (true) {
+                spin_lock(&inode->i_lock);
+                if (!(inode->i_state & I_DIRTY)) {
+                        inode->i_data.backing_dev_info = dst;
+                        spin_unlock(&inode->i_lock);
+                        return;
+                }
+                spin_unlock(&inode->i_lock);
+                WARN_ON_ONCE(write_inode_now(inode, true));
         }
-        spin_unlock(&inode->i_lock);
-        spin_unlock(&old->wb.list_lock);
-        spin_unlock(&dst->wb.list_lock);
-
-        if (wakeup_bdi)
-                bdi_wakeup_thread_delayed(dst);
 }
 
 /* Kill _all_ buffers and pagecache , dirty or not.. */