writeback: Fix periodic writeback after fs mount

commit a5faeaf9109578e65e1a32e2a3e76c8b47e7dcb6 upstream.

Code in blkdev.c moves a device inode to default_backing_dev_info when
the last reference to the device is put and moves the device inode back
to its bdi when the first reference is acquired. This includes moving to
wb.b_dirty list if the device inode is dirty. The code however doesn't
setup timer to wake corresponding flusher thread and while wb.b_dirty
list is non-empty __mark_inode_dirty() will not set it up either. Thus
periodic writeback is effectively disabled until a sync(2) call which can
lead to unexpected data loss in case of crash or power failure.

Fix the problem by setting up a timer for periodic writeback in case we
add the first dirty inode to wb.b_dirty list in bdev_inode_switch_bdi().

Reported-by: Bert De Jonghe <Bert.DeJonghe@amplidata.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 97e4cb5b556998ee62cf17402bf56242a8336b94..b5eb8c1816184320888ab2a7582189dc7fb8674e 100644 (file)
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -55,13 +55,21 @@ EXPORT_SYMBOL(I_BDEV);
 static void bdev_inode_switch_bdi(struct inode *inode,
                        struct backing_dev_info *dst)
 {
+       bool wakeup_bdi = false;
+
        spin_lock(&inode_wb_list_lock);
        spin_lock(&inode->i_lock);
        inode->i_data.backing_dev_info = dst;
-       if (inode->i_state & I_DIRTY)
+       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);
+       }
        spin_unlock(&inode->i_lock);
        spin_unlock(&inode_wb_list_lock);
+
+       if (wakeup_bdi)
+               bdi_wakeup_thread_delayed(dst);
 }
 
 sector_t blkdev_max_block(struct block_device *bdev)