btrfs: tree-checker: Fix wrong check on max devid

btrfs: tree-checker: Fix wrong check on max devid

commit 8bb177d18f114358a57d8ae7e206861b48b8b4de upstream.

[BUG]
The following script will cause false alert on devid check.
  #!/bin/bash

  dev1=/dev/test/test
  dev2=/dev/test/scratch1
  mnt=/mnt/btrfs

  umount $dev1 &> /dev/null
  umount $dev2 &> /dev/null
  umount $mnt &> /dev/null

  mkfs.btrfs -f $dev1

  mount $dev1 $mnt

  _fail()
  {
          echo "!!! FAILED !!!"
          exit 1
  }

  for ((i = 0; i < 4096; i++)); do
          btrfs dev add -f $dev2 $mnt || _fail
          btrfs dev del $dev1 $mnt || _fail
          dev_tmp=$dev1
          dev1=$dev2
          dev2=$dev_tmp
  done

[CAUSE]
Tree-checker uses BTRFS_MAX_DEVS() and BTRFS_MAX_DEVS_SYS_CHUNK() as
upper limit for devid.  But we can have devid holes just like above
script.

So the check for devid is incorrect and could cause false alert.

[FIX]
Just remove the whole devid check.  We don't have any hard requirement
for devid assignment.

Furthermore, even devid could get corrupted by a bitflip, we still have
dev extents verification at mount time, so corrupted data won't sneak
in.

This fixes fstests btrfs/194.

Reported-by: Anand Jain <anand.jain@oracle.com>
Fixes: ab4ba2e13346 ("btrfs: tree-checker: Verify dev item")
CC: stable@vger.kernel.org # 5.2+
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
[bwh: Backported to 4.19: adjust context]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>