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

From: Qu Wenruo <[email-masked]>
Date: Wed, 28 Aug 2019 10:33:13 +0800

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 <[email-masked]>
Fixes: ab4ba2e13346 ("btrfs: tree-checker: Verify dev item")
CC: [email-masked] # 5.2+
Signed-off-by: Qu Wenruo <[email-masked]>
Reviewed-by: David Sterba <[email-masked]>
Signed-off-by: David Sterba <[email-masked]>
[bwh: Backported to 4.19: adjust context]
Signed-off-by: Ben Hutchings <[email-masked]>
---
 fs/btrfs/tree-checker.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/fs/btrfs/tree-checker.c b/fs/btrfs/tree-checker.c
index b5e7caeb28a2..a0222e6a11c5 100644
--- a/fs/btrfs/tree-checker.c
+++ b/fs/btrfs/tree-checker.c
@@ -629,7 +629,6 @@ static int check_dev_item(struct btrfs_fs_info *fs_info,
 			  struct btrfs_key *key, int slot)
 {
 	struct btrfs_dev_item *ditem;
-	u64 max_devid = max(BTRFS_MAX_DEVS(fs_info), BTRFS_MAX_DEVS_SYS_CHUNK);
 
 	if (key->objectid != BTRFS_DEV_ITEMS_OBJECTID) {
 		dev_item_err(fs_info, leaf, slot,
@@ -637,12 +636,6 @@ static int check_dev_item(struct btrfs_fs_info *fs_info,
 			     key->objectid, BTRFS_DEV_ITEMS_OBJECTID);
 		return -EUCLEAN;
 	}
-	if (key->offset > max_devid) {
-		dev_item_err(fs_info, leaf, slot,
-			     "invalid devid: has=%llu expect=[0, %llu]",
-			     key->offset, max_devid);
-		return -EUCLEAN;
-	}
 	ditem = btrfs_item_ptr(leaf, slot, struct btrfs_dev_item);
 	if (btrfs_device_id(leaf, ditem) != key->offset) {
 		dev_item_err(fs_info, leaf, slot,