[syzbot] [block?] [trace?] INFO: task hung in blk_trace_startstop

syzbot
2025-11-11T16:43:27Z

Hello,

syzbot found the following issue on:

HEAD commit: 4a0c9b339199 Merge tag 'probes-fixes-v6.18-rc4' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12323812580000
kernel config: https://syzkaller.appspot.com/x/.config?x=e46b8a1c645465a9
dashboard link: https://syzkaller.appspot.com/bug?extid=774863666ef5b025c9d0
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2d880d82a810/disk-4a0c9b33.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/75307faea32a/vmlinux-4a0c9b33.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9d3f4c38a2eb/bzImage-4a0c9b33.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+774863666ef5b025c9d0@syzkaller.appspotmail.com

INFO: task syz.6.3379:19656 blocked for more than 143 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.6.3379 state:D stack:28776 pid:19656 tgid:19654 ppid:16553 task_flags:0x400040 flags:0x00080002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5325 [inline]
__schedule+0x1798/0x4cc0 kernel/sched/core.c:6929
__schedule_loop kernel/sched/core.c:7011 [inline]
schedule+0x165/0x360 kernel/sched/core.c:7026
schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7083
__mutex_lock_common kernel/locking/mutex.c:676 [inline]
__mutex_lock+0x7e6/0x1350 kernel/locking/mutex.c:760
blk_trace_startstop+0xa3/0x640 kernel/trace/blktrace.c:682
blk_trace_ioctl+0x19b/0x430 kernel/trace/blktrace.c:724
blkdev_common_ioctl+0xdf4/0x2550 block/ioctl.c:630
blkdev_ioctl+0x4f6/0x6d0 block/ioctl.c:699
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+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fbcfcb8f6c9
RSP: 002b:00007fbcfdaa3038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fbcfcde6090 RCX: 00007fbcfcb8f6c9
RDX: 0000000000000000 RSI: 0000000000001275 RDI: 0000000000000003
RBP: 00007fbcfcc11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fbcfcde6128 R14: 00007fbcfcde6090 R15: 00007fbcfcf0fa28
</TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/31:
#0: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
#0: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline]
#0: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180 kernel/locking/lockdep.c:6775
2 locks held by getty/5588:
#0: ffff888032fa10a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
#1: ffffc9000332b2f0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x43e/0x1400 drivers/tty/n_tty.c:2222
3 locks held by syz.6.3379/19655:
1 lock held by syz.6.3379/19656:
#0: ffff888142f2b068 (&q->debugfs_mutex){+.+.}-{4:4}, at: blk_trace_startstop+0xa3/0x640 kernel/trace/blktrace.c:682

=============================================

NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 31 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
nmi_cpu_backtrace+0x39e/0x3d0 lib/nmi_backtrace.c:113
nmi_trigger_cpumask_backtrace+0x17a/0x300 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:160 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:332 [inline]
watchdog+0xf60/0xfa0 kernel/hung_task.c:495
kthread+0x711/0x8a0 kernel/kthread.c:463
ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 19655 Comm: syz.6.3379 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
RIP: 0010:unwind_get_return_address+0x4d/0x90 arch/x86/kernel/unwind_orc.c:369
Code: c0 75 4c 83 3b 00 74 3a 48 83 c3 48 49 89 df 49 c1 ef 03 43 80 3c 37 00 74 08 48 89 df e8 4b 30 b2 00 48 8b 3b e8 b3 cf 18 00 <85> c0 74 14 43 80 3c 37 00 74 08 48 89 df e8 30 30 b2 00 48 8b 03
RSP: 0018:ffffc9000b257668 EFLAGS: 00000202
RAX: 0000000000000001 RBX: ffffc9000b2576d0 RCX: 6861806b914a4f00
RDX: 0000000000000001 RSI: ffffffff8d8f46a3 RDI: ffffffff846da7ad
RBP: ffffc9000b257710 R08: ffffc9000b257dd0 R09: 0000000000000000
R10: ffffc9000b2576d8 R11: fffff5200164aedd R12: ffff888066a03c80
R13: 1ffff9200164aefc R14: dffffc0000000000 R15: 1ffff9200164aeda
FS: 00007fbcfdac46c0(0000) GS:ffff88812623b000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f184bdb3ad8 CR3: 0000000043d28000 CR4: 00000000003526f0
Call Trace:
<TASK>
arch_stack_walk+0xfc/0x150 arch/x86/kernel/stacktrace.c:26
stack_trace_save+0x9c/0xe0 kernel/stacktrace.c:122
save_stack+0xf5/0x1f0 mm/page_owner.c:156
__reset_page_owner+0x71/0x1f0 mm/page_owner.c:311
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1394 [inline]
__free_frozen_pages+0xbc4/0xd30 mm/page_alloc.c:2906
relay_destroy_buf+0x10e/0x3a0 kernel/relay.c:200
relay_remove_buf kernel/relay.c:220 [inline]
kref_put include/linux/kref.h:65 [inline]
relay_close_buf kernel/relay.c:435 [inline]
relay_open+0x734/0x920 kernel/relay.c:531
do_blk_trace_setup+0x561/0x980 kernel/trace/blktrace.c:572
blk_trace_setup+0x116/0x1f0 kernel/trace/blktrace.c:614
blk_trace_ioctl+0x181/0x430 kernel/trace/blktrace.c:712
blkdev_ioctl+0x41d/0x6d0 block/ioctl.c:694
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+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fbcfcb8f6c9
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:00007fbcfdac4038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fbcfcde5fa0 RCX: 00007fbcfcb8f6c9
RDX: 00002000000000c0 RSI: 00000000c0481273 RDI: 0000000000000003
RBP: 00007fbcfcc11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fbcfcde6038 R14: 00007fbcfcde5fa0 R15: 00007fbcfcf0fa28
</TASK>

---
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