On Tue, May 8, 2018 at 9:15 AM, robbieko <robbieko@xxxxxxxxxxxx> wrote:
> From: Robbie Ko <robbieko@xxxxxxxxxxxx>
>
> [BUG]
> btrfs send BUG on parent commit_root node receive destination
> is at the same volume.
I can't make sense of that sentence.
>
> [Example]
> btrfs send -e -p /mnt/snap1/ /mnt/snap2/ | btrfs receive -e /mnt/temp
So, is -e necessary?
So doing that, for any parent and send snapshots, triggers the bug?
(and regardless of -e)
If that was enough I'm pretty sure almost everyone would be reporting
send/receive as unusable.
Please clarify.
>
> [REASON]
> 1. When send with the parent, the send process will get the parent
> commit_root(A), then send commit_root(B) and then compare the
> tree between A and B.
> 2. The receive process will take snapshot from parent, then the parent
> commit_root changes from A to C, so A will be released.
I don't understand this. How can the commit_root change?
The snapshot is readonly, it's can't be modified after it's created.
> 3. Then A will be assigned to other leaf nodes.
> 4. Therefore, the send process will use invalid A, resulting in
> invalid memory access.
>
> [FIX]
> We create new root and copy from parent/send commit_root to
> avoid invalid memory access.
>
> CallTrace looks like this:
> ------------[ cut here ]------------
> kernel BUG at fs/btrfs/ctree.c:1861!
> invalid opcode: 0000 [#1] SMP
> CPU: 6 PID: 24235 Comm: btrfs Tainted: P O 3.10.105 #23721
3.10 kernel....
You should reproduce any bugs you find on more recent kernels...
> ffff88046652d680 ti: ffff88041b720000 task.ti: ffff88041b720000
> RIP: 0010:[<ffffffffa08dd0e8>] read_node_slot+0x108/0x110 [btrfs]
> RSP: 0018:ffff88041b723b68 EFLAGS: 00010246
> RAX: ffff88043ca6b000 RBX: ffff88041b723c50 RCX: ffff880000000000
> RDX: 000000000000004c RSI: ffff880314b133f8 RDI: ffff880458b24000
> RBP: 0000000000000000 R08: 0000000000000001 R09: ffff88041b723c66
> R10: 0000000000000001 R11: 0000000000001000 R12: ffff8803f3e48890
> R13: ffff8803f3e48880 R14: ffff880466351800 R15: 0000000000000001
> FS: 00007f8c321dc8c0(0000) GS:ffff88047fcc0000(0000)
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> R2: 00007efd1006d000 CR3: 0000000213a24000 CR4: 00000000003407e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Stack:
> ffff88041b723c50 ffff8803f3e48880 ffff8803f3e48890 ffff8803f3e48880
> ffff880466351800 0000000000000001 ffffffffa08dd9d7 ffff88041b723c50
> ffff8803f3e48880 ffff88041b723c66 ffffffffa08dde85 a9ff88042d2c4400
> Call Trace:
> [<ffffffffa08dd9d7>] ? tree_move_down.isra.33+0x27/0x50 [btrfs]
> [<ffffffffa08dde85>] ? tree_advance+0xb5/0xc0 [btrfs]
> [<ffffffffa08e83d4>] ? btrfs_compare_trees+0x2d4/0x760 [btrfs]
> [<ffffffffa0982050>] ? finish_inode_if_needed+0x870/0x870 [btrfs]
> [<ffffffffa09841ea>] ? btrfs_ioctl_send+0xeda/0x1050 [btrfs]
> [<ffffffffa094bd3d>] ? btrfs_ioctl+0x1e3d/0x33f0 [btrfs]
> [<ffffffff81111133>] ? handle_pte_fault+0x373/0x990
> [<ffffffff8153a096>] ? atomic_notifier_call_chain+0x16/0x20
> [<ffffffff81063256>] ? set_task_cpu+0xb6/0x1d0
> [<ffffffff811122c3>] ? handle_mm_fault+0x143/0x2a0
> [<ffffffff81539cc0>] ? __do_page_fault+0x1d0/0x500
> [<ffffffff81062f07>] ? check_preempt_curr+0x57/0x90
> [<ffffffff8115075a>] ? do_vfs_ioctl+0x4aa/0x990
> [<ffffffff81034f83>] ? do_fork+0x113/0x3b0
> [<ffffffff812dd7d7>] ? trace_hardirqs_off_thunk+0x3a/0x6c
> [<ffffffff81150cc8>] ? SyS_ioctl+0x88/0xa0
> [<ffffffff8153e422>] ? system_call_fastpath+0x16/0x1b
> ---[ end trace 29576629ee80b2e1 ]---
>
> Signed-off-by: Robbie Ko <robbieko@xxxxxxxxxxxx>
> ---
> fs/btrfs/ctree.c | 26 ++++++++++++++++++++++++--
> 1 file changed, 24 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
> index b88a79e..c9ce52f 100644
> --- a/fs/btrfs/ctree.c
> +++ b/fs/btrfs/ctree.c
> @@ -5398,6 +5398,8 @@ int btrfs_compare_trees(struct btrfs_root *left_root,
> u64 right_blockptr;
> u64 left_gen;
> u64 right_gen;
> + struct extent_buffer *left_root_node = NULL;
> + struct extent_buffer *right_root_node = NULL;
>
> left_path = btrfs_alloc_path();
> if (!left_path) {
> @@ -5416,6 +5418,20 @@ int btrfs_compare_trees(struct btrfs_root *left_root,
> goto out;
> }
>
> + left_root_node = alloc_dummy_extent_buffer(left_root->fs_info, 0);
> + if (!left_root_node) {
> + ret = -ENOMEM;
> + goto out;
> + }
> + extent_buffer_get(left_root_node);
> +
> + right_root_node = alloc_dummy_extent_buffer(left_root->fs_info, 0);
> + if (!right_root_node) {
> + ret = -ENOMEM;
> + goto out;
> + }
> + extent_buffer_get(right_root_node);
> +
> left_path->search_commit_root = 1;
> left_path->skip_locking = 1;
> right_path->search_commit_root = 1;
> @@ -5460,12 +5476,16 @@ int btrfs_compare_trees(struct btrfs_root *left_root,
> down_read(&fs_info->commit_root_sem);
> left_level = btrfs_header_level(left_root->commit_root);
> left_root_level = left_level;
> - left_path->nodes[left_level] = left_root->commit_root;
> + copy_extent_buffer_full(left_root_node, left_root->commit_root);
> + set_bit(EXTENT_BUFFER_UPTODATE, &left_root_node->bflags);
> + left_path->nodes[left_level] = left_root_node;
> extent_buffer_get(left_path->nodes[left_level]);
>
> right_level = btrfs_header_level(right_root->commit_root);
> right_root_level = right_level;
> - right_path->nodes[right_level] = right_root->commit_root;
> + copy_extent_buffer_full(right_root_node, right_root->commit_root);
> + set_bit(EXTENT_BUFFER_UPTODATE, &right_root_node->bflags);
> + right_path->nodes[right_level] = right_root_node;
> extent_buffer_get(right_path->nodes[right_level]);
> up_read(&fs_info->commit_root_sem);
>
> @@ -5613,6 +5633,8 @@ int btrfs_compare_trees(struct btrfs_root *left_root,
> out:
> btrfs_free_path(left_path);
> btrfs_free_path(right_path);
> + free_extent_buffer(left_root_node);
> + free_extent_buffer(right_root_node);
> kvfree(tmp_buf);
> return ret;
> }
> --
> 1.9.1
>
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--
Filipe David Manana,
“Whether you think you can, or you think you can't — you're right.”
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