[PATCH 4/5] btrfs: extent-tree: Kill the BUG_ON() in insert_inline_extent_backref()

[Qu Wenruo <wqu@suse.com>]

[BUG]
With crafted image, btrfs can panic at insert_inline_extent_backref():
  kernel BUG at fs/btrfs/extent-tree.c:1857!
  invalid opcode: 0000 [#1] SMP PTI
  CPU: 0 PID: 1117 Comm: btrfs-transacti Not tainted 5.0.0-rc8+ #9
  RIP: 0010:insert_inline_extent_backref+0xcc/0xe0
  Code: 45 20 49 8b 7e 50 49 89 d8 4c 8b 4d 10 48 8b 55 c8 4c 89 e1 41 57 4c 89 ee 50 ff 75 18 e8 cc bf ff ff 31 c0 48 83 c4 18 eb b2 <0f> 0b e8 9d df bd ff 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 66 66
  RSP: 0018:ffffac4dc1287be8 EFLAGS: 00010293
  RAX: 0000000000000000 RBX: 0000000000000007 RCX: 0000000000000001
  RDX: 0000000000001000 RSI: 0000000000000000 RDI: 0000000000000000
  RBP: ffffac4dc1287c28 R08: ffffac4dc1287ab8 R09: ffffac4dc1287ac0
  R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
  R13: ffff8febef88a540 R14: ffff8febeaa7bc30 R15: 0000000000000000
  FS: 0000000000000000(0000) GS:ffff8febf7a00000(0000) knlGS:0000000000000000
  CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 00007f663ace94c0 CR3: 0000000235698006 CR4: 00000000000206f0
  Call Trace:
  ? _cond_resched+0x1a/0x50
  __btrfs_inc_extent_ref.isra.64+0x7e/0x240
  ? btrfs_merge_delayed_refs+0xa5/0x330
  __btrfs_run_delayed_refs+0x653/0x1120
  btrfs_run_delayed_refs+0xdb/0x1b0
  btrfs_commit_transaction+0x52/0x950
  ? start_transaction+0x94/0x450
  transaction_kthread+0x163/0x190
  kthread+0x105/0x140
  ? btrfs_cleanup_transaction+0x560/0x560
  ? kthread_destroy_worker+0x50/0x50
  ret_from_fork+0x35/0x40
  Modules linked in:
  ---[ end trace 2ad8b3de903cf825 ]---

[CAUSE]
Due to extent tree corruption (still valid by itself, but bad cross ref),
we can allocate an extent which is still in extent tree.

Then we will try to insert/update inlined extent backref line for the
existing tree block, and triggering the BUG_ON() where we don't expect
to increase refs on non-subvolume tree block.

[FIX]
Replace that BUG_ON() with proper error message and leaf dump for debug
build.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=202829
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/extent-tree.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 199e4eed8f2d..72868d9ac58e 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -1856,7 +1856,24 @@ int insert_inline_extent_backref(struct btrfs_trans_handle *trans,
 					   num_bytes, parent, root_objectid,
 					   owner, offset, 1);
 	if (ret == 0) {
-		BUG_ON(owner < BTRFS_FIRST_FREE_OBJECTID);
+		/*
+		 * We're adding ref to an existing tree block, only happens
+		 * when creating snapshots, not possible to other trees.
+		 */
+		if (owner < BTRFS_FIRST_FREE_OBJECTID) {
+			WARN(IS_ENABLED(CONFIG_BTRFS_DEBUG), KERN_ERR
+			"invalid operation for non-subvolume tree block");
+
+			btrfs_crit(trans->fs_info,
+"invalid operation, adding refs to a non-subvolume tree block, bytenr=%llu num_bytes=%llu root_objectid=%llu",
+				   bytenr, num_bytes, root_objectid);
+			if (IS_ENABLED(CONFIG_BTRFS_DEBUG)) {
+				btrfs_crit(trans->fs_info,
+			"path->slots[0]=%d path->nodes[0]:", path->slots[0]);
+				btrfs_print_leaf(path->nodes[0]);
+			}
+			return -EUCLEAN;
+		}
 		update_inline_extent_backref(path, iref, refs_to_add,
 					     extent_op, NULL);
 	} else if (ret == -ENOENT) {
@@ -2073,6 +2090,9 @@ int btrfs_inc_extent_ref(struct btrfs_trans_handle *trans,
 /*
  * __btrfs_inc_extent_ref - insert backreference for a given extent
  *
+ * The work is opposite as __btrfs_free_extent().
+ * For more info about how it works or examples, refer to __btrfs_free_extent().
+ *
  * @trans:	    Handle of transaction
  *
  * @node:	    The delayed ref node used to get the bytenr/length for
@@ -2153,9 +2173,9 @@ static int __btrfs_inc_extent_ref(struct btrfs_trans_handle *trans,
 	/* now insert the actual backref */
 	ret = insert_extent_backref(trans, path, bytenr, parent, root_objectid,
 				    owner, offset, refs_to_add);
+out:
 	if (ret)
 		btrfs_abort_transaction(trans, ret);
-out:
 	btrfs_free_path(path);
 	return ret;
 }
-- 
2.22.0