[PATCH 2/2] dm-bdev-keep-bdev-always-referenced.patch

[Mikulas Patocka <mpatocka@redhat.com>]

Always keep the reference to structure block_device.

Reference to block_device is obtained with function bdget_disk (and is released
with bdput.

bdget_disk was called while the device was being suspended, in dm_suspend() ---
however at this point, there could be another devices already suspended.

bdget_disk can wait for IO and allocate memory and this could result in waiting
for already suspended device, resulting in deadlock.

It caused bug https://bugzilla.redhat.com/show_bug.cgi?id=179786

This patch changes the code so that it gets the reference to struct block_device
when struct mapped_device is allocated and initialized in (alloc_dev) and drops
the reference when it is destroyed in free_dev. Thus, there is no call to
bdget_disk, while any device is suspended.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 drivers/md/dm.c |   37 +++++++++----------------------------
 1 file changed, 9 insertions(+), 28 deletions(-)

Index: linux-2.6.30-rc2-devel/drivers/md/dm.c
===================================================================
--- linux-2.6.30-rc2-devel.orig/drivers/md/dm.c	2009-04-15 16:24:19.000000000 +0200
+++ linux-2.6.30-rc2-devel/drivers/md/dm.c	2009-04-15 16:24:25.000000000 +0200
@@ -1183,6 +1183,10 @@ static struct mapped_device *alloc_dev(i
 	if (!md->wq)
 		goto bad_thread;
 
+	md->bdev = bdget_disk(md->disk, 0);
+	if (!md->bdev)
+		goto bad_bdev;
+
 	/* Populate the mapping, nobody knows we exist yet */
 	spin_lock(&_minor_lock);
 	old_md = idr_replace(&_minor_idr, md, minor);
@@ -1192,6 +1196,8 @@ static struct mapped_device *alloc_dev(i
 
 	return md;
 
+bad_bdev:
+	destroy_workqueue(md->wq);
 bad_thread:
 	put_disk(md->disk);
 bad_disk:
@@ -1217,10 +1223,8 @@ static void free_dev(struct mapped_devic
 {
 	int minor = MINOR(disk_devt(md->disk));
 
-	if (md->bdev) {
-		unlock_fs(md);
-		bdput(md->bdev);
-	}
+	unlock_fs(md);
+	bdput(md->bdev);
 	destroy_workqueue(md->wq);
 	mempool_destroy(md->tio_pool);
 	mempool_destroy(md->io_pool);
@@ -1280,8 +1284,7 @@ static int __bind(struct mapped_device *
 	if (size != get_capacity(md->disk))
 		memset(&md->geometry, 0, sizeof(md->geometry));
 
-	if (md->bdev)
-		__set_size(md, size);
+	__set_size(md, size);
 
 	if (!size) {
 		dm_table_destroy(t);
@@ -1523,11 +1526,6 @@ int dm_swap_table(struct mapped_device *
 	if (!dm_suspended(md))
 		goto out;
 
-	/* without bdev, the device size cannot be changed */
-	if (!md->bdev)
-		if (get_capacity(md->disk) != dm_table_get_size(table))
-			goto out;
-
 	__unbind(md);
 	r = __bind(md, table);
 
@@ -1606,13 +1604,6 @@ int dm_suspend(struct mapped_device *md,
 
 	/* bdget() can stall if the pending I/Os are not flushed */
 	if (!noflush) {
-		md->bdev = bdget_disk(md->disk, 0);
-		if (!md->bdev) {
-			DMWARN("bdget failed in dm_suspend");
-			r = -ENOMEM;
-			goto out;
-		}
-
 		/*
 		 * Flush I/O to the device. noflush supersedes do_lockfs,
 		 * because lock_fs() needs to flush I/Os.
@@ -1678,11 +1669,6 @@ int dm_suspend(struct mapped_device *md,
 	set_bit(DMF_SUSPENDED, &md->flags);
 
 out:
-	if (r && md->bdev) {
-		bdput(md->bdev);
-		md->bdev = NULL;
-	}
-
 	dm_table_put(map);
 
 out_unlock:
@@ -1711,11 +1697,6 @@ int dm_resume(struct mapped_device *md)
 
 	unlock_fs(md);
 
-	if (md->bdev) {
-		bdput(md->bdev);
-		md->bdev = NULL;
-	}
-
 	clear_bit(DMF_SUSPENDED, &md->flags);
 
 	dm_table_unplug_all(map);