Btrfs: fix incorrect space accounting after failure to insert inline extent

When using compression, if we fail to insert an inline extent we
incorrectly end up attempting to free the reserved data space twice,
once through extent_clear_unlock_delalloc(), because we pass it the
flag EXTENT_DO_ACCOUNTING, and once through a direct call to
btrfs_free_reserved_data_space_noquota(). This results in a trace
like the following:

[  834.576240] ------------[ cut here ]------------
[  834.576825] WARNING: CPU: 2 PID: 486 at fs/btrfs/extent-tree.c:4316 btrfs_free_reserved_data_space_noquota+0x60/0x9f [btrfs]
[  834.579501] Modules linked in: btrfs crc32c_generic xor raid6_pq ppdev i2c_piix4 acpi_cpufreq psmouse tpm_tis parport_pc pcspkr serio_raw tpm_tis_core sg parport evdev i2c_core tpm button loop autofs4 ext4 crc16 jbd2 mbcache sr_mod cdrom sd_mod ata_generic virtio_scsi ata_piix virtio_pci libata virtio_ring virtio scsi_mod e1000 floppy [last unloaded: btrfs]
[  834.592116] CPU: 2 PID: 486 Comm: kworker/u32:4 Not tainted 4.10.0-rc8-btrfs-next-37+ #2
[  834.593316] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.9.1-0-gb3ef39f-prebuilt.qemu-project.org 04/01/2014
[  834.595273] Workqueue: btrfs-delalloc btrfs_delalloc_helper [btrfs]
[  834.596103] Call Trace:
[  834.596103]  dump_stack+0x67/0x90
[  834.596103]  __warn+0xc2/0xdd
[  834.596103]  warn_slowpath_null+0x1d/0x1f
[  834.596103]  btrfs_free_reserved_data_space_noquota+0x60/0x9f [btrfs]
[  834.596103]  compress_file_range.constprop.42+0x2fa/0x3fc [btrfs]
[  834.596103]  ? submit_compressed_extents+0x3a7/0x3a7 [btrfs]
[  834.596103]  async_cow_start+0x32/0x4d [btrfs]
[  834.596103]  btrfs_scrubparity_helper+0x187/0x3e7 [btrfs]
[  834.596103]  btrfs_delalloc_helper+0xe/0x10 [btrfs]
[  834.596103]  process_one_work+0x273/0x4e4
[  834.596103]  worker_thread+0x1eb/0x2ca
[  834.596103]  ? rescuer_thread+0x2b6/0x2b6
[  834.596103]  kthread+0x100/0x108
[  834.596103]  ? __list_del_entry+0x22/0x22
[  834.596103]  ret_from_fork+0x2e/0x40
[  834.611656] ---[ end trace 719902fe6bdef08f ]---

So fix this by not calling directly btrfs_free_reserved_data_space_noquota()
if an error happened.
Signed-off-by: Filipe Manana <fdmanana@suse.com>

fs/btrfs/inode.c

@@ -590,8 +590,10 @@ static noinline void compress_file_range(struct inode *inode,
 						     PAGE_SET_WRITEBACK |
 						     page_error_op |
 						     PAGE_END_WRITEBACK);
-			btrfs_free_reserved_data_space_noquota(inode, start,
-						end - start + 1);
+			if (ret == 0)
+				btrfs_free_reserved_data_space_noquota(inode,
+							       start,
+							       end - start + 1);
 			goto free_pages_out;
 		}
 	}