[PATCH v3 2/2] btrfs: reset device back to allocation state when removing

[Johannes Thumshirn <jthumshirn@suse.de>]

When closing a device, btrfs_close_one_device() first allocates a new
device, copies the device to close's name, replaces it in the dev_list
with the copy and then finally frees it.

This involves two memory allocation, which can potentially fail. As this
code path is tricky to unwind, the allocation failures where handled by
BUG_ON()s.

But this copying isn't strictly needed, all that is needed is resetting
the device in question to it's state it had after the allocation.

Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
---
 fs/btrfs/volumes.c | 34 +++++++++++++++-------------------
 1 file changed, 15 insertions(+), 19 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 2398b071bcf6..3d04fa4a0ba6 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1064,38 +1064,34 @@ static void btrfs_close_bdev(struct btrfs_device *device)
 static void btrfs_close_one_device(struct btrfs_device *device)
 {
 	struct btrfs_fs_devices *fs_devices = device->fs_devices;
-	struct btrfs_device *new_device;
-	struct rcu_string *name;
 
 	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) &&
 	    device->devid != BTRFS_DEV_REPLACE_DEVID) {
 		list_del_init(&device->dev_alloc_list);
 		fs_devices->rw_devices--;
 	}
+	clear_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
 
-	if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state))
+	if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state)) {
 		fs_devices->missing_devices--;
+		clear_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state);
+	}
 
+	clear_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state);
 	btrfs_close_bdev(device);
-	if (device->bdev)
+	if (device->bdev) {
 		fs_devices->open_devices--;
-
-	new_device = btrfs_alloc_device(NULL, &device->devid,
-					device->uuid);
-	BUG_ON(IS_ERR(new_device)); /* -ENOMEM */
-
-	/* Safe because we are under uuid_mutex */
-	if (device->name) {
-		name = rcu_string_strdup(device->name->str, GFP_NOFS);
-		BUG_ON(!name); /* -ENOMEM */
-		rcu_assign_pointer(new_device->name, name);
+		device->bdev = NULL;
 	}
 
-	list_replace_rcu(&device->dev_list, &new_device->dev_list);
-	new_device->fs_devices = device->fs_devices;
-
-	synchronize_rcu();
-	btrfs_free_device(device);
+	/* Verify the device is back in a pristine state  */
+	ASSERT(!test_bit(BTRFS_DEV_STATE_FLUSH_SENT, &device->dev_state));
+	ASSERT(!test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state));
+	ASSERT(list_empty(&device->dev_alloc_list));
+	ASSERT(list_empty(&device->post_commit_list));
+	ASSERT(atomic_read(&device->reada_in_flight) == 0);
+	ASSERT(atomic_read(&device->dev_stats_ccnt) == 0);
+	ASSERT(RB_EMPTY_ROOT(&device->alloc_state.state));
 }
 
 static int close_fs_devices(struct btrfs_fs_devices *fs_devices)
-- 
2.16.4