Re: recent bdi changes result in WARN_ON on luksClose / dm

[Jens Axboe <jens.axboe@oracle.com>]

On Sat, Sep 12 2009, Jens Axboe wrote:
> On Sat, Sep 12 2009, Sebastian Andrzej Siewior wrote:
> > | Orion:/# cryptsetup luksClose crypto
> > |------------[ cut here ]------------
> > |WARNING: at /home/bigeasy/git/cryptodev-2.6/mm/backing-dev.c:637 bdi_destroy+0x44/0x60()
> > |Modules linked in: cbc sha256_generic dm_crypt [last unloaded: mv_cesa]
> > |[<c0028dd8>] (unwind_backtrace+0x0/0xdc) from [<c003adb0>] (warn_slowpath_common+0x4c/0x80)
> > |[<c003adb0>] (warn_slowpath_common+0x4c/0x80) from [<c007f2e0>] (bdi_destroy+0x44/0x60)
> > |[<c007f2e0>] (bdi_destroy+0x44/0x60) from [<c012e3a0>] (blk_release_queue+0x3c/0x54)
> > |[<c012e3a0>] (blk_release_queue+0x3c/0x54) from [<c01399a8>] (kobject_release+0x5c/0x74)
> > |[<c01399a8>] (kobject_release+0x5c/0x74) from [<c013a6ac>] (kref_put+0x68/0x7c)
> > |[<c013a6ac>] (kref_put+0x68/0x7c) from [<c01b7098>] (dm_put+0x148/0x178)
> > |[<c01b7098>] (dm_put+0x148/0x178) from [<c01bb82c>] (dev_remove+0x98/0xb4)
> > |[<c01bb82c>] (dev_remove+0x98/0xb4) from [<c01bbec0>] (dm_ctl_ioctl+0x21c/0x29c)
> > |[<c01bbec0>] (dm_ctl_ioctl+0x21c/0x29c) from [<c00a153c>] (vfs_ioctl+0x2c/0x8c)
> > |[<c00a153c>] (vfs_ioctl+0x2c/0x8c) from [<c00a1bac>] (do_vfs_ioctl+0x524/0x590)
> > |[<c00a1bac>] (do_vfs_ioctl+0x524/0x590) from [<c00a1c50>] (sys_ioctl+0x38/0x5c)
> > |[<c00a1c50>] (sys_ioctl+0x38/0x5c) from [<c0023e80>] (ret_fast_syscall+0x0/0x2c)
> > |---[ end trace b3c544a14b51605c ]---
> 
> So dm is killing the queue and associated backing device, while dirty
> inodes still exist. That's not very nice. Perhaps dm_lock_for_deletion()
> should ensure that the backing is flushed?

Don't count this as a real fix, I'll investigate closer on monday. Does
the warning go away with this hack? It'll ensure that pending dirty
inodes are flushed.

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index b4845b1..ead4a9b 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -357,6 +357,17 @@ int dm_open_count(struct mapped_device *md)
 	return atomic_read(&md->open_count);
 }
 
+static void dm_flush_dirty_io(struct mapped_device *md)
+{
+	struct writeback_control wbc = {
+		.bdi		= &md->queue->backing_dev_info,
+		.sync_mode	= WB_SYNC_ALL,
+		.nr_to_write	= LONG_MAX,
+	};
+
+	bdi_start_writeback(&wbc);
+}
+
 /*
  * Guarantees nothing is using the device before it's deleted.
  */
@@ -373,6 +384,9 @@ int dm_lock_for_deletion(struct mapped_device *md)
 
 	spin_unlock(&_minor_lock);
 
+	if (!r)
+		dm_flush_dirty_io(md);
+
 	return r;
 }
 

-- 
Jens Axboe