ext4: fix sleep inside spinlock issue with quota and dealloc (#14739)

Unlock i_block_reservation_lock before vfs_dq_reserve_block().
This patch fixes http://bugzilla.kernel.org/show_bug.cgi?id=14739

CC: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/ext4/inode.c

@@ -1816,19 +1816,17 @@ repeat:
 
 	md_needed = mdblocks - EXT4_I(inode)->i_reserved_meta_blocks;
 	total = md_needed + nrblocks;
+	spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
 
 	/*
 	 * Make quota reservation here to prevent quota overflow
 	 * later. Real quota accounting is done at pages writeout
 	 * time.
 	 */
-	if (vfs_dq_reserve_block(inode, total)) {
-		spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
+	if (vfs_dq_reserve_block(inode, total))
 		return -EDQUOT;
-	}
 
 	if (ext4_claim_free_blocks(sbi, total)) {
-		spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
 		vfs_dq_release_reservation_block(inode, total);
 		if (ext4_should_retry_alloc(inode->i_sb, &retries)) {
 			yield();
@@ -1836,10 +1834,11 @@ repeat:
 		}
 		return -ENOSPC;
 	}
+	spin_lock(&EXT4_I(inode)->i_block_reservation_lock);
 	EXT4_I(inode)->i_reserved_data_blocks += nrblocks;
-	EXT4_I(inode)->i_reserved_meta_blocks = mdblocks;
-
+	EXT4_I(inode)->i_reserved_meta_blocks += md_needed;
 	spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
+
 	return 0;       /* success */
 }