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

Nikolay Borisov
2019-07-10T11:12:25Z

On 10.07.19 г. 11:02 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.
>
> 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");

Again, the text of the warn doesn't bring any value, make it plain
WARN_ON(IS_ENABLED())

> +
> + 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:

I think this silently fixes a bug if insert_inline_extent_backref fails.
If that's the case then it should be in a dedicated patch with an
explicit rationale

> btrfs_free_path(path);
> return ret;
> }
>