Merge git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstable

* git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstable:
  Btrfs: prevent RAID level downgrades when space is low
  Btrfs: account for missing devices in RAID allocation profiles
  Btrfs: EIO when we fail to read tree roots
  Btrfs: fix compiler warnings
  Btrfs: Make async snapshot ioctl more generic
  Btrfs: pwrite blocked when writing from the mmaped buffer of the same page
  Btrfs: Fix a crash when mounting a subvolume
  Btrfs: fix sync subvol/snapshot creation
  Btrfs: Fix page leak in compressed writeback path
  Btrfs: do not BUG if we fail to remove the orphan item for dead snapshots
  Btrfs: fixup return code for btrfs_del_orphan_item
  Btrfs: do not do fast caching if we are allocating blocks for tree_root
  Btrfs: deal with space cache errors better
  Btrfs: fix use after free in O_DIRECT

fs/btrfs/disk-io.c

@@ -696,6 +696,7 @@ static int btree_submit_bio_hook(struct inode *inode, int rw, struct bio *bio,
 				   __btree_submit_bio_done);
 }
 
+#ifdef CONFIG_MIGRATION
 static int btree_migratepage(struct address_space *mapping,
 			struct page *newpage, struct page *page)
 {
@@ -712,12 +713,9 @@ static int btree_migratepage(struct address_space *mapping,
 	if (page_has_private(page) &&
 	    !try_to_release_page(page, GFP_KERNEL))
 		return -EAGAIN;
-#ifdef CONFIG_MIGRATION
 	return migrate_page(mapping, newpage, page);
-#else
-	return -ENOSYS;
-#endif
 }
+#endif
 
 static int btree_writepage(struct page *page, struct writeback_control *wbc)
 {
@@ -1009,7 +1007,10 @@ static int find_and_setup_root(struct btrfs_root *tree_root,
 	blocksize = btrfs_level_size(root, btrfs_root_level(&root->root_item));
 	root->node = read_tree_block(root, btrfs_root_bytenr(&root->root_item),
 				     blocksize, generation);
-	BUG_ON(!root->node);
+	if (!root->node || !btrfs_buffer_uptodate(root->node, generation)) {
+		free_extent_buffer(root->node);
+		return -EIO;
+	}
 	root->commit_root = btrfs_root_node(root);
 	return 0;
 }

fs/btrfs/extent-tree.c

@@ -429,6 +429,7 @@ static int caching_kthread(void *data)
 
 static int cache_block_group(struct btrfs_block_group_cache *cache,
 			     struct btrfs_trans_handle *trans,
+			     struct btrfs_root *root,
 			     int load_cache_only)
 {
 	struct btrfs_fs_info *fs_info = cache->fs_info;
@@ -442,9 +443,12 @@ static int cache_block_group(struct btrfs_block_group_cache *cache,
 
 	/*
 	 * We can't do the read from on-disk cache during a commit since we need
-	 * to have the normal tree locking.
+	 * to have the normal tree locking.  Also if we are currently trying to
+	 * allocate blocks for the tree root we can't do the fast caching since
+	 * we likely hold important locks.
 	 */
-	if (!trans->transaction->in_commit) {
+	if (!trans->transaction->in_commit &&
+	    (root && root != root->fs_info->tree_root)) {
 		spin_lock(&cache->lock);
 		if (cache->cached != BTRFS_CACHE_NO) {
 			spin_unlock(&cache->lock);
@@ -2741,6 +2745,7 @@ static int cache_save_setup(struct btrfs_block_group_cache *block_group,
 	struct btrfs_root *root = block_group->fs_info->tree_root;
 	struct inode *inode = NULL;
 	u64 alloc_hint = 0;
+	int dcs = BTRFS_DC_ERROR;
 	int num_pages = 0;
 	int retries = 0;
 	int ret = 0;
@@ -2795,6 +2800,8 @@ static int cache_save_setup(struct btrfs_block_group_cache *block_group,
 
 	spin_lock(&block_group->lock);
 	if (block_group->cached != BTRFS_CACHE_FINISHED) {
+		/* We're not cached, don't bother trying to write stuff out */
+		dcs = BTRFS_DC_WRITTEN;
 		spin_unlock(&block_group->lock);
 		goto out_put;
 	}
@@ -2821,6 +2828,8 @@ static int cache_save_setup(struct btrfs_block_group_cache *block_group,
 	ret = btrfs_prealloc_file_range_trans(inode, trans, 0, 0, num_pages,
 					      num_pages, num_pages,
 					      &alloc_hint);
+	if (!ret)
+		dcs = BTRFS_DC_SETUP;
 	btrfs_free_reserved_data_space(inode, num_pages);
 out_put:
 	iput(inode);
@@ -2828,10 +2837,7 @@ static int cache_save_setup(struct btrfs_block_group_cache *block_group,
 	btrfs_release_path(root, path);
 out:
 	spin_lock(&block_group->lock);
-	if (ret)
-		block_group->disk_cache_state = BTRFS_DC_ERROR;
-	else
-		block_group->disk_cache_state = BTRFS_DC_SETUP;
+	block_group->disk_cache_state = dcs;
 	spin_unlock(&block_group->lock);
 
 	return ret;
@@ -3037,7 +3043,13 @@ 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);
@@ -4080,7 +4092,7 @@ static int update_block_group(struct btrfs_trans_handle *trans,
 		 * space back to the block group, otherwise we will leak space.
 		 */
 		if (!alloc && cache->cached == BTRFS_CACHE_NO)
-			cache_block_group(cache, trans, 1);
+			cache_block_group(cache, trans, NULL, 1);
 
 		byte_in_group = bytenr - cache->key.objectid;
 		WARN_ON(byte_in_group > cache->key.offset);
@@ -4930,11 +4942,31 @@ static noinline int find_free_extent(struct btrfs_trans_handle *trans,
 		btrfs_get_block_group(block_group);
 		search_start = block_group->key.objectid;
 
+		/*
+		 * this can happen if we end up cycling through all the
+		 * raid types, but we want to make sure we only allocate
+		 * for the proper type.
+		 */
+		if (!block_group_bits(block_group, data)) {
+		    u64 extra = BTRFS_BLOCK_GROUP_DUP |
+				BTRFS_BLOCK_GROUP_RAID1 |
+				BTRFS_BLOCK_GROUP_RAID10;
+
+			/*
+			 * if they asked for extra copies and this block group
+			 * doesn't provide them, bail.  This does allow us to
+			 * fill raid0 from raid1.
+			 */
+			if ((data & extra) && !(block_group->flags & extra))
+				goto loop;
+		}
+
 have_block_group:
 		if (unlikely(block_group->cached == BTRFS_CACHE_NO)) {
 			u64 free_percent;
 
-			ret = cache_block_group(block_group, trans, 1);
+			ret = cache_block_group(block_group, trans,
+						orig_root, 1);
 			if (block_group->cached == BTRFS_CACHE_FINISHED)
 				goto have_block_group;
 
@@ -4958,7 +4990,8 @@ static noinline int find_free_extent(struct btrfs_trans_handle *trans,
 			if (loop > LOOP_CACHING_NOWAIT ||
 			    (loop > LOOP_FIND_IDEAL &&
 			     atomic_read(&space_info->caching_threads) < 2)) {
-				ret = cache_block_group(block_group, trans, 0);
+				ret = cache_block_group(block_group, trans,
+							orig_root, 0);
 				BUG_ON(ret);
 			}
 			found_uncached_bg = true;
@@ -5515,7 +5548,7 @@ int btrfs_alloc_logged_file_extent(struct btrfs_trans_handle *trans,
 	u64 num_bytes = ins->offset;
 
 	block_group = btrfs_lookup_block_group(root->fs_info, ins->objectid);
-	cache_block_group(block_group, trans, 0);
+	cache_block_group(block_group, trans, NULL, 0);
 	caching_ctl = get_caching_control(block_group);
 
 	if (!caching_ctl) {
@@ -6300,9 +6333,13 @@ int btrfs_drop_snapshot(struct btrfs_root *root,
 					   NULL, NULL);
 		BUG_ON(ret < 0);
 		if (ret > 0) {
-			ret = btrfs_del_orphan_item(trans, tree_root,
-						    root->root_key.objectid);
-			BUG_ON(ret);
+			/* if we fail to delete the orphan item this time
+			 * around, it'll get picked up the next time.
+			 *
+			 * The most common failure here is just -ENOENT.
+			 */
+			btrfs_del_orphan_item(trans, tree_root,
+					      root->root_key.objectid);
 		}
 	}
 
@@ -7878,7 +7915,14 @@ 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;
@@ -8247,7 +8291,6 @@ int btrfs_read_block_groups(struct btrfs_root *root)
 			break;
 		if (ret != 0)
 			goto error;
-
 		leaf = path->nodes[0];
 		btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
 		cache = kzalloc(sizeof(*cache), GFP_NOFS);

fs/btrfs/file.c

@@ -48,30 +48,34 @@ static noinline int btrfs_copy_from_user(loff_t pos, int num_pages,
 					 struct page **prepared_pages,
 					 struct iov_iter *i)
 {
-	size_t copied;
+	size_t copied = 0;
 	int pg = 0;
 	int offset = pos & (PAGE_CACHE_SIZE - 1);
+	int total_copied = 0;
 
 	while (write_bytes > 0) {
 		size_t count = min_t(size_t,
 				     PAGE_CACHE_SIZE - offset, write_bytes);
 		struct page *page = prepared_pages[pg];
-again:
-		if (unlikely(iov_iter_fault_in_readable(i, count)))
-			return -EFAULT;
-
-		/* Copy data from userspace to the current page */
-		copied = iov_iter_copy_from_user(page, i, offset, count);
+		/*
+		 * Copy data from userspace to the current page
+		 *
+		 * Disable pagefault to avoid recursive lock since
+		 * the pages are already locked
+		 */
+		pagefault_disable();
+		copied = iov_iter_copy_from_user_atomic(page, i, offset, count);
+		pagefault_enable();
 
 		/* Flush processor's dcache for this page */
 		flush_dcache_page(page);
 		iov_iter_advance(i, copied);
 		write_bytes -= copied;
+		total_copied += copied;
 
+		/* Return to btrfs_file_aio_write to fault page */
 		if (unlikely(copied == 0)) {
-			count = min_t(size_t, PAGE_CACHE_SIZE - offset,
-				      iov_iter_single_seg_count(i));
-			goto again;
+			break;
 		}
 
 		if (unlikely(copied < PAGE_CACHE_SIZE - offset)) {
@@ -81,7 +85,7 @@ static noinline int btrfs_copy_from_user(loff_t pos, int num_pages,
 			offset = 0;
 		}
 	}
-	return 0;
+	return total_copied;
 }
 
 /*
@@ -854,6 +858,8 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
 	unsigned long last_index;
 	int will_write;
 	int buffered = 0;
+	int copied = 0;
+	int dirty_pages = 0;
 
 	will_write = ((file->f_flags & O_DSYNC) || IS_SYNC(inode) ||
 		      (file->f_flags & O_DIRECT));
@@ -970,7 +976,17 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
 		WARN_ON(num_pages > nrptrs);
 		memset(pages, 0, sizeof(struct page *) * nrptrs);
 
-		ret = btrfs_delalloc_reserve_space(inode, write_bytes);
+		/*
+		 * Fault pages before locking them in prepare_pages
+		 * to avoid recursive lock
+		 */
+		if (unlikely(iov_iter_fault_in_readable(&i, write_bytes))) {
+			ret = -EFAULT;
+			goto out;
+		}
+
+		ret = btrfs_delalloc_reserve_space(inode,
+					num_pages << PAGE_CACHE_SHIFT);
 		if (ret)
 			goto out;
 
@@ -978,37 +994,49 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
 				    pos, first_index, last_index,
 				    write_bytes);
 		if (ret) {
-			btrfs_delalloc_release_space(inode, write_bytes);
+			btrfs_delalloc_release_space(inode,
+					num_pages << PAGE_CACHE_SHIFT);
 			goto out;
 		}
 
-		ret = btrfs_copy_from_user(pos, num_pages,
+		copied = btrfs_copy_from_user(pos, num_pages,
 					   write_bytes, pages, &i);
-		if (ret == 0) {
+		dirty_pages = (copied + PAGE_CACHE_SIZE - 1) >>
+					PAGE_CACHE_SHIFT;
+
+		if (num_pages > dirty_pages) {
+			if (copied > 0)
+				atomic_inc(
+					&BTRFS_I(inode)->outstanding_extents);
+			btrfs_delalloc_release_space(inode,
+					(num_pages - dirty_pages) <<
+					PAGE_CACHE_SHIFT);
+		}
+
+		if (copied > 0) {
 			dirty_and_release_pages(NULL, root, file, pages,
-						num_pages, pos, write_bytes);
+						dirty_pages, pos, copied);
 		}
 
 		btrfs_drop_pages(pages, num_pages);
-		if (ret) {
-			btrfs_delalloc_release_space(inode, write_bytes);
-			goto out;
-		}
 
-		if (will_write) {
-			filemap_fdatawrite_range(inode->i_mapping, pos,
-						 pos + write_bytes - 1);
-		} else {
-			balance_dirty_pages_ratelimited_nr(inode->i_mapping,
-							   num_pages);
-			if (num_pages <
-			    (root->leafsize >> PAGE_CACHE_SHIFT) + 1)
-				btrfs_btree_balance_dirty(root, 1);
-			btrfs_throttle(root);
+		if (copied > 0) {
+			if (will_write) {
+				filemap_fdatawrite_range(inode->i_mapping, pos,
+							 pos + copied - 1);
+			} else {
+				balance_dirty_pages_ratelimited_nr(
+							inode->i_mapping,
+							dirty_pages);
+				if (dirty_pages <
+				(root->leafsize >> PAGE_CACHE_SHIFT) + 1)
+					btrfs_btree_balance_dirty(root, 1);
+				btrfs_throttle(root);
+			}
 		}
 
-		pos += write_bytes;
-		num_written += write_bytes;
+		pos += copied;
+		num_written += copied;
 
 		cond_resched();
 	}

fs/btrfs/free-space-cache.c

@@ -290,7 +290,7 @@ int load_free_space_cache(struct btrfs_fs_info *fs_info,
 		       (unsigned long long)BTRFS_I(inode)->generation,
 		       (unsigned long long)generation,
 		       (unsigned long long)block_group->key.objectid);
-		goto out;
+		goto free_cache;
 	}
 
 	if (!num_entries)
@@ -524,6 +524,12 @@ int btrfs_write_out_cache(struct btrfs_root *root,
 		return 0;
 	}
 
+	node = rb_first(&block_group->free_space_offset);
+	if (!node) {
+		iput(inode);
+		return 0;
+	}
+
 	last_index = (i_size_read(inode) - 1) >> PAGE_CACHE_SHIFT;
 	filemap_write_and_wait(inode->i_mapping);
 	btrfs_wait_ordered_range(inode, inode->i_size &
@@ -543,10 +549,6 @@ int btrfs_write_out_cache(struct btrfs_root *root,
 	 */
 	first_page_offset = (sizeof(u32) * num_checksums) + sizeof(u64);
 
-	node = rb_first(&block_group->free_space_offset);
-	if (!node)
-		goto out_free;
-
 	/*
 	 * Lock all pages first so we can lock the extent safely.
 	 *

fs/btrfs/inode.c

@@ -495,7 +495,7 @@ static noinline int compress_file_range(struct inode *inode,
 		add_async_extent(async_cow, start, num_bytes,
 				 total_compressed, pages, nr_pages_ret);
 
-		if (start + num_bytes < end && start + num_bytes < actual_end) {
+		if (start + num_bytes < end) {
 			start += num_bytes;
 			pages = NULL;
 			cond_resched();
@@ -5712,9 +5712,9 @@ static void btrfs_end_dio_bio(struct bio *bio, int err)
 
 	if (err) {
 		printk(KERN_ERR "btrfs direct IO failed ino %lu rw %lu "
-		      "disk_bytenr %lu len %u err no %d\n",
-		      dip->inode->i_ino, bio->bi_rw, bio->bi_sector,
-		      bio->bi_size, err);
+		      "sector %#Lx len %u err no %d\n",
+		      dip->inode->i_ino, bio->bi_rw,
+		      (unsigned long long)bio->bi_sector, bio->bi_size, err);
 		dip->errors = 1;
 
 		/*
@@ -5934,8 +5934,7 @@ static void btrfs_submit_direct(int rw, struct bio *bio, struct inode *inode,
 	 */
 	if (write) {
 		struct btrfs_ordered_extent *ordered;
-		ordered = btrfs_lookup_ordered_extent(inode,
-						      dip->logical_offset);
+		ordered = btrfs_lookup_ordered_extent(inode, file_offset);
 		if (!test_bit(BTRFS_ORDERED_PREALLOC, &ordered->flags) &&
 		    !test_bit(BTRFS_ORDERED_NOCOW, &ordered->flags))
 			btrfs_free_reserved_extent(root, ordered->start,

fs/btrfs/ioctl.c

@@ -947,23 +947,42 @@ static noinline int btrfs_ioctl_snap_create_transid(struct file *file,
 
 static noinline int btrfs_ioctl_snap_create(struct file *file,
 					    void __user *arg, int subvol,
-					    int async)
+					    int v2)
 {
 	struct btrfs_ioctl_vol_args *vol_args = NULL;
-	struct btrfs_ioctl_async_vol_args *async_vol_args = NULL;
+	struct btrfs_ioctl_vol_args_v2 *vol_args_v2 = NULL;
 	char *name;
 	u64 fd;
-	u64 transid = 0;
 	int ret;
 
-	if (async) {
-		async_vol_args = memdup_user(arg, sizeof(*async_vol_args));
-		if (IS_ERR(async_vol_args))
-			return PTR_ERR(async_vol_args);
+	if (v2) {
+		u64 transid = 0;
+		u64 *ptr = NULL;
 
-		name = async_vol_args->name;
-		fd = async_vol_args->fd;
-		async_vol_args->name[BTRFS_SNAPSHOT_NAME_MAX] = '\0';
+		vol_args_v2 = memdup_user(arg, sizeof(*vol_args_v2));
+		if (IS_ERR(vol_args_v2))
+			return PTR_ERR(vol_args_v2);
+
+		if (vol_args_v2->flags & ~BTRFS_SUBVOL_CREATE_ASYNC) {
+			ret = -EINVAL;
+			goto out;
+		}
+
+		name = vol_args_v2->name;
+		fd = vol_args_v2->fd;
+		vol_args_v2->name[BTRFS_SUBVOL_NAME_MAX] = '\0';
+
+		if (vol_args_v2->flags & BTRFS_SUBVOL_CREATE_ASYNC)
+			ptr = &transid;
+
+		ret = btrfs_ioctl_snap_create_transid(file, name, fd,
+						      subvol, ptr);
+
+		if (ret == 0 && ptr &&
+		    copy_to_user(arg +
+				 offsetof(struct btrfs_ioctl_vol_args_v2,
+					  transid), ptr, sizeof(*ptr)))
+			ret = -EFAULT;
 	} else {
 		vol_args = memdup_user(arg, sizeof(*vol_args));
 		if (IS_ERR(vol_args))
@@ -971,20 +990,13 @@ static noinline int btrfs_ioctl_snap_create(struct file *file,
 		name = vol_args->name;
 		fd = vol_args->fd;
 		vol_args->name[BTRFS_PATH_NAME_MAX] = '\0';
-	}
-
-	ret = btrfs_ioctl_snap_create_transid(file, name, fd,
-					      subvol, &transid);
 
-	if (!ret && async) {
-		if (copy_to_user(arg +
-				offsetof(struct btrfs_ioctl_async_vol_args,
-				transid), &transid, sizeof(transid)))
-			return -EFAULT;
+		ret = btrfs_ioctl_snap_create_transid(file, name, fd,
+						      subvol, NULL);
 	}
-
+out:
 	kfree(vol_args);
-	kfree(async_vol_args);
+	kfree(vol_args_v2);
 
 	return ret;
 }
@@ -2246,7 +2258,7 @@ long btrfs_ioctl(struct file *file, unsigned int
 		return btrfs_ioctl_getversion(file, argp);
 	case BTRFS_IOC_SNAP_CREATE:
 		return btrfs_ioctl_snap_create(file, argp, 0, 0);
-	case BTRFS_IOC_SNAP_CREATE_ASYNC:
+	case BTRFS_IOC_SNAP_CREATE_V2:
 		return btrfs_ioctl_snap_create(file, argp, 0, 1);
 	case BTRFS_IOC_SUBVOL_CREATE:
 		return btrfs_ioctl_snap_create(file, argp, 1, 0);

fs/btrfs/ioctl.h

@@ -30,11 +30,15 @@ struct btrfs_ioctl_vol_args {
 	char name[BTRFS_PATH_NAME_MAX + 1];
 };
 
-#define BTRFS_SNAPSHOT_NAME_MAX 4079
-struct btrfs_ioctl_async_vol_args {
+#define BTRFS_SUBVOL_CREATE_ASYNC	(1ULL << 0)
+
+#define BTRFS_SUBVOL_NAME_MAX 4039
+struct btrfs_ioctl_vol_args_v2 {
 	__s64 fd;
 	__u64 transid;
-	char name[BTRFS_SNAPSHOT_NAME_MAX + 1];
+	__u64 flags;
+	__u64 unused[4];
+	char name[BTRFS_SUBVOL_NAME_MAX + 1];
 };
 
 #define BTRFS_INO_LOOKUP_PATH_MAX 4080
@@ -187,6 +191,6 @@ struct btrfs_ioctl_space_args {
 				    struct btrfs_ioctl_space_args)
 #define BTRFS_IOC_START_SYNC _IOR(BTRFS_IOCTL_MAGIC, 24, __u64)
 #define BTRFS_IOC_WAIT_SYNC  _IOW(BTRFS_IOCTL_MAGIC, 22, __u64)
-#define BTRFS_IOC_SNAP_CREATE_ASYNC _IOW(BTRFS_IOCTL_MAGIC, 23, \
-				   struct btrfs_ioctl_async_vol_args)
+#define BTRFS_IOC_SNAP_CREATE_V2 _IOW(BTRFS_IOCTL_MAGIC, 23, \
+				   struct btrfs_ioctl_vol_args_v2)
 #endif

fs/btrfs/orphan.c

@@ -56,8 +56,12 @@ int btrfs_del_orphan_item(struct btrfs_trans_handle *trans,
 		return -ENOMEM;
 
 	ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
-	if (ret)
+	if (ret < 0)
 		goto out;
+	if (ret) {
+		ret = -ENOENT;
+		goto out;
+	}
 
 	ret = btrfs_del_item(trans, root, path);
 

fs/btrfs/super.c

@@ -685,9 +685,9 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
 		mutex_unlock(&root->d_inode->i_mutex);
 
 		if (IS_ERR(new_root)) {
+			dput(root);
 			deactivate_locked_super(s);
 			error = PTR_ERR(new_root);
-			dput(root);
 			goto error_free_subvol_name;
 		}
 		if (!new_root->d_inode) {

fs/btrfs/volumes.c

@@ -412,12 +412,16 @@ 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) {
@@ -1236,6 +1240,9 @@ 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)
@@ -3080,7 +3087,9 @@ 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);
@@ -3278,6 +3287,15 @@ 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;
 		}
 	}
 

fs/btrfs/volumes.h

@@ -44,6 +44,7 @@ struct btrfs_device {
 
 	int writeable;
 	int in_fs_metadata;
+	int missing;
 
 	spinlock_t io_lock;
 
@@ -93,6 +94,7 @@ 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;