3 files changed, 36 insertions, 3 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 41133b0..4be231e 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3044,7 +3044,13 @@ static void set_avail_alloc_bits(struct btrfs_fs_info *fs_info, u64 flags)
 
 u64 btrfs_reduce_alloc_profile(struct btrfs_root *root, u64 flags)
 {
-	u64 num_devices = root->fs_info->fs_devices->rw_devices;
+	/*
+	 * we add in the count of missing devices because we want
+	 * to make sure that any RAID levels on a degraded FS
+	 * continue to be honored.
+	 */
+	u64 num_devices = root->fs_info->fs_devices->rw_devices +
+		root->fs_info->fs_devices->missing_devices;
 
 	if (num_devices == 1)
 		flags &= ~(BTRFS_BLOCK_GROUP_RAID1 | BTRFS_BLOCK_GROUP_RAID0);
@@ -7891,7 +7897,14 @@ static u64 update_block_group_flags(struct btrfs_root *root, u64 flags)
 	u64 stripped = BTRFS_BLOCK_GROUP_RAID0 |
 		BTRFS_BLOCK_GROUP_RAID1 | BTRFS_BLOCK_GROUP_RAID10;
 
-	num_devices = root->fs_info->fs_devices->rw_devices;
+	/*
+	 * we add in the count of missing devices because we want
+	 * to make sure that any RAID levels on a degraded FS
+	 * continue to be honored.
+	 */
+	num_devices = root->fs_info->fs_devices->rw_devices +
+		root->fs_info->fs_devices->missing_devices;
+
 	if (num_devices == 1) {
 		stripped |= BTRFS_BLOCK_GROUP_DUP;
 		stripped = flags & ~stripped;
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 91851b5..177b731 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -413,12 +413,16 @@ static noinline int device_list_add(const char *path,
 
 		device->fs_devices = fs_devices;
 		fs_devices->num_devices++;
-	} else if (strcmp(device->name, path)) {
+	} else if (!device->name || strcmp(device->name, path)) {
 		name = kstrdup(path, GFP_NOFS);
 		if (!name)
 			return -ENOMEM;
 		kfree(device->name);
 		device->name = name;
+		if (device->missing) {
+			fs_devices->missing_devices--;
+			device->missing = 0;
+		}
 	}
 
 	if (found_transid > fs_devices->latest_trans) {
@@ -1238,6 +1242,9 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
 
 	device->fs_devices->num_devices--;
 
+	if (device->missing)
+		root->fs_info->fs_devices->missing_devices--;
+
 	next_device = list_entry(root->fs_info->fs_devices->devices.next,
 				 struct btrfs_device, dev_list);
 	if (device->bdev == root->fs_info->sb->s_bdev)
@@ -3084,7 +3091,9 @@ static struct btrfs_device *add_missing_dev(struct btrfs_root *root,
 	device->devid = devid;
 	device->work.func = pending_bios_fn;
 	device->fs_devices = fs_devices;
+	device->missing = 1;
 	fs_devices->num_devices++;
+	fs_devices->missing_devices++;
 	spin_lock_init(&device->io_lock);
 	INIT_LIST_HEAD(&device->dev_alloc_list);
 	memcpy(device->uuid, dev_uuid, BTRFS_UUID_SIZE);
@@ -3282,6 +3291,15 @@ static int read_one_dev(struct btrfs_root *root,
 			device = add_missing_dev(root, devid, dev_uuid);
 			if (!device)
 				return -ENOMEM;
+		} else if (!device->missing) {
+			/*
+			 * this happens when a device that was properly setup
+			 * in the device info lists suddenly goes bad.
+			 * device->bdev is NULL, and so we have to set
+			 * device->missing to one here
+			 */
+			root->fs_info->fs_devices->missing_devices++;
+			device->missing = 1;
 		}
 	}
 
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 31b0fab..a668c01 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -45,6 +45,7 @@ struct btrfs_device {
 	int barriers;
 	int writeable;
 	int in_fs_metadata;
+	int missing;
 
 	spinlock_t io_lock;
 
@@ -94,6 +95,7 @@ struct btrfs_fs_devices {
 	u64 num_devices;
 	u64 open_devices;
 	u64 rw_devices;
+	u64 missing_devices;
 	u64 total_rw_bytes;
 	struct block_device *latest_bdev;