Re: [bug report]kernel BUG at fs/btrfs/zoned.c:2587! triggered by blktests zbd/009

[Johannes Thumshirn <Johannes.Thumshirn@wdc.com>]

On 9/3/25 10:36 AM, Yi Zhang wrote:
> The kernel BUG was triggered by blktests zbd/009 on v6.17-rc3, please
> help check it and let me know if you need any infor/test for it,
> thanks.
[...]
> [  319.819821] assertion failed: bg->zone_unusable == 0 :: 0, in
> fs/btrfs/zoned.c:2587
> [  319.828449] ------------[ cut here ]------------
> [  319.833618] kernel BUG at fs/btrfs/zoned.c:2587!
> [  319.838793] Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
> [  319.844829] CPU: 3 UID: 0 PID: 1370 Comm: mount Tainted: G        W
>           ------  ---
> 6.17.0-0.rc3.250826gfab1beda7597.32.fc44.x86_64+debug #1 PREEMPT(lazy)
> [  319.860948] Tainted: [W]=WARN
> [  319.864259] Hardware name: Dell Inc. PowerEdge R730/0WCJNT, BIOS
> 2.19.0 12/12/2023
> [  319.872704] RIP: 0010:btrfs_zoned_reserve_data_reloc_bg.cold+0xb2/0xb4
> [  319.880014] Code: ab e8 7e ab f7 ff 0f 0b 41 b8 1b 0a 00 00 48 c7
> c1 80 9f 59 ab 31 d2 48 c7 c6 20 b8 59 ab 48 c7 c7 20 a0 59 ab e8 5a
> ab f7 ff <0f> 0b 41 b8 5f 0a 00 00 48 c7 c1 80 9f 59 ab 31 d2 48 c7 c6
> 00 b9
> [  319.900977] RSP: 0018:ffffc9000c21f930 EFLAGS: 00010282
> [  319.906816] RAX: 0000000000000047 RBX: ffff8888d1a54000 RCX: 0000000000000000
> [  319.914783] RDX: 0000000000000047 RSI: 1ffffffff629cc84 RDI: fffff52001843f18
> [  319.922742] RBP: ffff888121b7c000 R08: ffffffffa802cbb5 R09: fffff52001843edc
> [  319.930709] R10: 0000000000000003 R11: 0000000000000001 R12: 0000000000000000
> [  319.938666] R13: 0000000000000001 R14: ffff888121b7c128 R15: ffff88810f379800
> [  319.946625] FS:  00007fbd89e98840(0000) GS:ffff8890af8e8000(0000)
> knlGS:0000000000000000
> [  319.955661] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  319.962077] CR2: 0000559e0ad4b540 CR3: 00000008e14ce003 CR4: 00000000003726f0
> [  319.970046] Call Trace:
> [  319.972767]  <TASK>
> [  319.975102]  ? create_space_info+0x155/0x390
> [  319.979880]  open_ctree+0x1874/0x2203
> [  319.983977]  btrfs_fill_super.cold+0x2c/0x16d
> [  319.988850]  btrfs_get_tree_super+0x936/0xd60
> [  319.993725]  btrfs_get_tree_subvol+0x230/0x5f0
>

OK the problem is, we're ASSERTing if zone_unusable is 0 and that 
obviously fails, because zbd/009 configures scsi_debug with a zone_size 
of 4MB and a zone_capacity of 3MB. This automatically leads to an 
assertion failure as bg->zone_unusable is 1MB.

The test in there is to check if we have an empty block-group.
@Naohiro what do you think of the following:

diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
index 6e66ec491181..f897f914b78e 100644
--- a/fs/btrfs/zoned.c
+++ b/fs/btrfs/zoned.c
@@ -2590,7 +2590,8 @@ void btrfs_zoned_reserve_data_reloc_bg(struct 
btrfs_fs_info *fs_info)
                         space_info->disk_total -= bg->length * factor;
                         /* There is no allocation ever happened. */
                         ASSERT(bg->used == 0);
-                       ASSERT(bg->zone_unusable == 0);
+                       ASSERT(bg->zone_unusable == 0 ||
+                              bg->length - bg->zone_unusable == 
bg->zone_capacity);
                         /* No super block in a block group on the zoned 
setup. */
                         ASSERT(bg->bytes_super == 0);
                         spin_unlock(&space_info->lock);