Re: [PATCH v2 4/5] btrfs: extent-tree: Kill the BUG_ON() in insert_inline_extent_backref()

[Nikolay Borisov <nborisov@suse.com>]

On 25.07.19 г. 9:12 ч., Qu Wenruo wrote:
> [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.
> The offending tree block of that case is from csum tree.
> The newly allocated tree block is also for csum tree.
> 
> Then we will try to insert an tree block ref for the existing tree block
> ref.
> 
> For btrfs tree extent item, a tree block can never be shared directly by
> the same tree twice.
> We have such BUG_ON() to prevent such problem, but BUG_ON() is
> definitely not good enough.
> 
> [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>

Reviewed-by: Nikolay Borisov <nborisov@suse.com>

> ---
>  fs/btrfs/extent-tree.c | 20 +++++++++++++++++++-
>  1 file changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 74e4b138218e..19dd9148a3aa 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -1856,7 +1856,22 @@ 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 refs to an tree block we already own, this
> +		 * should not happen at all.
> +		 */
> +		if (owner < BTRFS_FIRST_FREE_OBJECTID) {
> +			btrfs_crit(trans->fs_info,
> +"invalid operation, adding refs to an existing tree ref, bytenr=%llu num_bytes=%llu root_objectid=%llu",
> +				   bytenr, num_bytes, root_objectid);
> +			if (IS_ENABLED(CONFIG_BTRFS_DEBUG)) {
> +				WARN_ON(1);
> +				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 +2088,9 @@ 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
>