------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 1 PID: 7640 at lib/refcount.c:28 refcount_warn_saturate+0x11b/0x1a0 lib/refcount.c:28
Modules linked in:
CPU: 1 PID: 7640 Comm: syz.0.882 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
RIP: 0010:refcount_warn_saturate+0x11b/0x1a0 lib/refcount.c:28
Code: 09 01 48 c7 c7 20 c8 79 8a e8 a1 e7 cd 05 0f 0b eb c4 e8 48 34 95 fd c6 05 46 4e 92 09 01 48 c7 c7 80 c8 79 8a e8 85 e7 cd 05 <0f> 0b eb a8 e8 2c 34 95 fd c6 05 27 4e 92 09 01 48 c7 c7 c0 c7 79
RSP: 0018:ffffc9000cfe7a20 EFLAGS: 00010246
RAX: 7f337e60b7e30b00 RBX: 0000000000000003 RCX: ffff88807ed48000
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffffffff901d6187 R09: 1ffffffff203ac30
R10: dffffc0000000000 R11: fffffbfff203ac31 R12: 1ffff920019fcf83
R13: ffff888020caf000 R14: 0000000000000003 R15: ffffffff84e065d0
FS:  00007f74eb6f66c0(0000) GS:ffff8880b9000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000560cb0bb9190 CR3: 000000007a6d5000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 bt_tags_iter+0x23a/0x2e0 block/blk-mq-tag.c:307
 __sbitmap_for_each_set include/linux/sbitmap.h:263 [inline]
 sbitmap_for_each_set+0x271/0x490 include/linux/sbitmap.h:284
 bt_tags_for_each block/blk-mq-tag.c:334 [inline]
 __blk_mq_all_tag_iter block/blk-mq-tag.c:345 [inline]
 blk_mq_tagset_busy_iter+0x2b2/0x3a0 block/blk-mq-tag.c:386
 nbd_clear_que drivers/block/nbd.c:864 [inline]
 nbd_clear_sock drivers/block/nbd.c:1255 [inline]
 nbd_clear_sock_ioctl drivers/block/nbd.c:1394 [inline]
 __nbd_ioctl drivers/block/nbd.c:1422 [inline]
 nbd_ioctl+0x2cf/0xe70 drivers/block/nbd.c:1482
 blkdev_ioctl+0x33b/0x700 block/ioctl.c:604
 block_ioctl+0xac/0xf0 block/fops.c:496
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f74ec4a93b9
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:00007f74eb6f6028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f74ec6af080 RCX: 00007f74ec4a93b9
RDX: 0000000000000000 RSI: 000000000000ab04 RDI: 0000000000000003
RBP: 00007f74ec534974 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000001 R14: 00007f74ec6af080 R15: 00007fff1af7bab8
 </TASK>