[PATCH] btrfs: tree-checker: Don't check device size as we can have valid 0 total_bytes

[Qu Wenruo <wqu@suse.com>]

Under the following call traces, btrfs can commit device with 0
total_bytes onto disk:
btrfs_rm_device()
|- btrfs_shrink_device()
|  |- btrfs_device_set_total_bytes(device, 0)
|  |- btrfs_update_device()
|  |- btrfs_commit_transaction() #1
|- btrfs_rm_dev_item()

This will trigger write time tree checker warning.
And further more, this can create valid btrfs with device->total_bytes
== 0 and triggering read time tree-checker if power loss happens after
above transaction #1 but before next transaction.

So this dev item check is too restrict.

Please fold this patch into commit 87d87c6dcbbe ("btrfs: tree-checker:
Verify dev item") in misc-next branch.

The fuzzed image can be already addressed by commit 1b3922a8bc74
("btrfs: Use real device structure to verify dev extent") thus we don't
need that strict check anymore.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/tree-checker.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/fs/btrfs/tree-checker.c b/fs/btrfs/tree-checker.c
index d2c3c1f8870d..974208ac56da 100644
--- a/fs/btrfs/tree-checker.c
+++ b/fs/btrfs/tree-checker.c
@@ -657,16 +657,11 @@ static int check_dev_item(struct extent_buffer *leaf,
 	}
 
 	/*
-	 * Since btrfs device add doesn't check device size at all, we could
-	 * have device item whose size is smaller than 1M which is useless, but
-	 * still valid.
-	 * So here we can only check the obviously wrong case.
+	 * For device total_bytes, we don't have solid way to check it, as it can
+	 * be 0 for device removal.
+	 * device size check can only be done by dev extents check.
 	 */
-	if (btrfs_device_total_bytes(leaf, ditem) == 0) {
-		dev_item_err(leaf, slot,
-			     "invalid total bytes: have 0");
-		return -EUCLEAN;
-	}
+
 	if (btrfs_device_bytes_used(leaf, ditem) >
 	    btrfs_device_total_bytes(leaf, ditem)) {
 		dev_item_err(leaf, slot,
-- 
2.21.0