[syzbot] [block?] WARNING in wbt_init_enable_default

[syzbot] [block?] WARNING in wbt_init_enable_default

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    b927546677c8 Merge tag 'dma-mapping-6.19-2025-12-22' of gi..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11dc8b92580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a94030c847137a18
dashboard link: https://syzkaller.appspot.com/bug?extid=71fcf20f7c1e5043d78c
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10515f1a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b27369f4b013/disk-b9275466.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3b2d81c4be86/vmlinux-b9275466.xz
kernel image: https://storage.googleapis.com/syzbot-assets/89c2ad4f36b6/bzImage-b9275466.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+71fcf20f7c1e5043d78c@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: block/blk-wbt.c:741 at wbt_init_enable_default+0x4e/0x60 block/blk-wbt.c:741, CPU#0: syz.1.439/7602
Modules linked in:
CPU: 0 UID: 0 PID: 7602 Comm: syz.1.439 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:wbt_init_enable_default+0x4e/0x60 block/blk-wbt.c:741
Code: ff 89 c6 e8 e4 e4 40 fd 85 db 75 18 e8 9b e0 40 fd 5b e9 20 2c 90 fc cc e8 8f e0 40 fd 5b e9 14 2c 90 fc cc e8 83 e0 40 fd 90 <0f> 0b 90 5b e9 04 2c 90 fc cc 0f 1f 84 00 00 00 00 00 90 90 90 90
RSP: 0018:ffffc90004ab7ab8 EFLAGS: 00010293
RAX: ffffffff848014fd RBX: 00000000fffffff4 RCX: ffff88802a78bd00
RDX: 0000000000000000 RSI: 00000000fffffff4 RDI: 0000000000000000
RBP: 1ffff11004165212 R08: ffffffff8f822277 R09: 1ffffffff1f0444e
R10: dffffc0000000000 R11: fffffbfff1f0444f R12: 0000000000000000
R13: 1ffff110051e05f7 R14: ffff888020b29000 R15: ffff888028f02fa8
FS:  00007f3ce68426c0(0000) GS:ffff888125e1f000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f999a972100 CR3: 000000007b2b2000 CR4: 0000000000350ef0
Call Trace:
 <TASK>
 blk_register_queue+0x36a/0x3f0 block/blk-sysfs.c:935
 __add_disk+0x677/0xd50 block/genhd.c:528
 add_disk_fwnode+0xfc/0x480 block/genhd.c:597
 add_disk include/linux/blkdev.h:785 [inline]
 loop_add+0x7f0/0xad0 drivers/block/loop.c:2093
 loop_control_get_free drivers/block/loop.c:2209 [inline]
 loop_control_ioctl+0x2f2/0x5a0 drivers/block/loop.c:2224
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3ce598f749
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f3ce6842038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f3ce5be6090 RCX: 00007f3ce598f749
RDX: 0000000000000000 RSI: 0000000000004c82 RDI: 0000000000000006
RBP: 00007f3ce5a13f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f3ce5be6128 R14: 00007f3ce5be6090 R15: 00007ffd72edd058
 </TASK>


---
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Re: [syzbot] [block?] WARNING in wbt_init_enable_default

[Ming Lei]

On Wed, Dec 24, 2025 at 11:34:21PM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    b927546677c8 Merge tag 'dma-mapping-6.19-2025-12-22' of gi..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=11dc8b92580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=a94030c847137a18
> dashboard link: https://syzkaller.appspot.com/bug?extid=71fcf20f7c1e5043d78c
> compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10515f1a580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/b27369f4b013/disk-b9275466.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/3b2d81c4be86/vmlinux-b9275466.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/89c2ad4f36b6/bzImage-b9275466.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+71fcf20f7c1e5043d78c@syzkaller.appspotmail.com
> 
> ------------[ cut here ]------------
> WARNING: block/blk-wbt.c:741 at wbt_init_enable_default+0x4e/0x60 block/blk-wbt.c:741, CPU#0: syz.1.439/7602
> Modules linked in:
> CPU: 0 UID: 0 PID: 7602 Comm: syz.1.439 Not tainted syzkaller #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
> RIP: 0010:wbt_init_enable_default+0x4e/0x60 block/blk-wbt.c:741

Looks like 'echo > /sys/block/loop0/queue/queue_wb_lat' creates wbt first,
then -EBUSY is triggered.

Seems -EBUSY should be filtered for warn here.

Thanks,
Ming

Re: [syzbot] [block?] WARNING in wbt_init_enable_default

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    37a93dd5c49b Merge tag 'net-next-7.0' of git://git.kernel...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14342c02580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a512b4a06724b76a
dashboard link: https://syzkaller.appspot.com/bug?extid=71fcf20f7c1e5043d78c
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16ffbdb2580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11542eef980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0dedaafff2ad/disk-37a93dd5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/aa7fae081497/vmlinux-37a93dd5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9096b39b53e1/bzImage-37a93dd5.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+71fcf20f7c1e5043d78c@syzkaller.appspotmail.com

0x000000000001-0x000000020000 : ""
ftl_cs: FTL header corrupt!
"mq-deadline" elevator initialization, failed -12, falling back to "none"
------------[ cut here ]------------
!rwb
WARNING: block/blk-wbt.c:784 at wbt_init_enable_default+0xcb/0x120 block/blk-wbt.c:784, CPU#0: syz.0.23/6066
Modules linked in:
CPU: 0 UID: 0 PID: 6066 Comm: syz.0.23 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
RIP: 0010:wbt_init_enable_default+0xcb/0x120 block/blk-wbt.c:784
Code: df e8 d9 cc a2 06 4c 89 e7 e8 e1 38 00 00 48 89 df e8 29 56 a2 06 e8 04 76 2b fd 5b 5d 41 5c e9 9b 22 a4 06 e8 f6 75 2b fd 90 <0f> 0b 90 eb 81 e8 eb 75 2b fd 90 0f 0b 90 48 b8 00 00 00 00 00 fc
RSP: 0018:ffffc90003b3f590 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff88803364e000 RCX: 0000000000000040
RDX: ffff88802e719e40 RSI: ffffffff84daf70a RDI: ffffffff8bfa9120
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: ffffffff82708ed4 R12: ffff88802b37a620
R13: ffff88803364e390 R14: ffff88802b37a630 R15: ffff88803364e090
FS:  00007f472043f6c0(0000) GS:ffff8881245a5000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00002000000da000 CR3: 000000007affe000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 blk_register_queue+0x39e/0x4e0 block/blk-sysfs.c:942
 __add_disk+0x73f/0xe40 block/genhd.c:528
 add_disk_fwnode+0x118/0x5c0 block/genhd.c:597
 add_mtd_blktrans_dev+0xd0b/0x1520 drivers/mtd/mtd_blkdevs.c:382
 mtdblock_add_mtd+0x1cc/0x270 drivers/mtd/mtdblock.c:333
 blktrans_notify_add drivers/mtd/mtd_blkdevs.c:464 [inline]
 blktrans_notify_add+0xa2/0xf0 drivers/mtd/mtd_blkdevs.c:456
 add_mtd_device+0xbe3/0x1750 drivers/mtd/mtdcore.c:820
 mtd_add_partition+0x30a/0x660 drivers/mtd/mtdpart.c:279
 mtdchar_blkpg_ioctl+0x207/0x250 drivers/mtd/mtdchar.c:562
 mtdchar_ioctl+0x1670/0x1fd0 drivers/mtd/mtdchar.c:1218
 mtdchar_unlocked_ioctl+0xb0/0xf0 drivers/mtd/mtdchar.c:1241
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f471f59bf79
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f472043f028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f471f816090 RCX: 00007f471f59bf79
RDX: 0000000000000000 RSI: 0000000000001269 RDI: 0000000000000004
RBP: 00007f471f6327e0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f471f816128 R14: 00007f471f816090 R15: 00007ffe9ebc84a8
 </TASK>


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

Re: [syzbot] [block?] WARNING in wbt_init_enable_default

[Ming Lei]

On Thu, Feb 12, 2026 at 12:41:30PM -0800, syzbot wrote:
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    37a93dd5c49b Merge tag 'net-next-7.0' of git://git.kernel...
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=14342c02580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=a512b4a06724b76a
> dashboard link: https://syzkaller.appspot.com/bug?extid=71fcf20f7c1e5043d78c
> compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16ffbdb2580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11542eef980000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/0dedaafff2ad/disk-37a93dd5.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/aa7fae081497/vmlinux-37a93dd5.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/9096b39b53e1/bzImage-37a93dd5.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+71fcf20f7c1e5043d78c@syzkaller.appspotmail.com
> 
> 0x000000000001-0x000000020000 : ""
> ftl_cs: FTL header corrupt!
> "mq-deadline" elevator initialization, failed -12, falling back to "none"
> ------------[ cut here ]------------
> !rwb
> WARNING: block/blk-wbt.c:784 at wbt_init_enable_default+0xcb/0x120 block/blk-wbt.c:784, CPU#0: syz.0.23/6066

The warning is expected given -ENOMEM is triggered from wbt_alloc(), either
kmalloc or percpu allocator.


Thanks,
Ming