[syzbot] [io-uring?] INFO: task hung in vfs_coredump

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 2aeda9592360 Add linux-next specific files for 20250627
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=12f9a982580000
kernel config: https://syzkaller.appspot.com/x/.config?x=7f5c1d958b70bf47
dashboard link: https://syzkaller.appspot.com/bug?extid=c29db0c6705a06cb65f2
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14ff688c580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d532560074a3/disk-2aeda959.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/483001f76864/vmlinux-2aeda959.xz
kernel image: https://storage.googleapis.com/syzbot-assets/8f233cdc1c77/bzImage-2aeda959.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c29db0...@syzkaller.appspotmail.com

INFO: task syz.0.23:6175 blocked for more than 143 seconds.
Not tainted 6.16.0-rc3-next-20250627-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.23 state:D stack:27624 pid:6175 tgid:6170 ppid:5972 task_flags:0x400640 flags:0x00004006
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5313 [inline]
__schedule+0x16f5/0x4d00 kernel/sched/core.c:6696
__schedule_loop kernel/sched/core.c:6774 [inline]
schedule+0x165/0x360 kernel/sched/core.c:6789
schedule_timeout+0x9a/0x270 kernel/time/sleep_timeout.c:75
do_wait_for_common kernel/sched/completion.c:100 [inline]
__wait_for_common+0x3da/0x710 kernel/sched/completion.c:121
wait_for_common kernel/sched/completion.c:132 [inline]
wait_for_completion_state+0x1c/0x40 kernel/sched/completion.c:269
coredump_wait fs/coredump.c:534 [inline]
vfs_coredump+0x8c2/0x2ab0 fs/coredump.c:1128
get_signal+0x1109/0x1340 kernel/signal.c:3019
arch_do_signal_or_restart+0x9a/0x750 arch/x86/kernel/signal.c:337
exit_to_user_mode_loop+0x75/0x110 kernel/entry/common.c:111
exit_to_user_mode_prepare include/linux/entry-common.h:330 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:414 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:449 [inline]
do_syscall_64+0x2bd/0x3b0 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f612984f830
RSP: 002b:00007f612a722b38 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: 0000000000000000 RBX: 00007f6129bb6088 RCX: 00007f612998e929
RDX: 00007f612a722b40 RSI: 00007f612a722c70 RDI: 000000000000000b
RBP: 00007f6129bb6080 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f6129bb608c
R13: 0000000000000000 R14: 00007fff3502f910 R15: 00007fff3502f9f8
</TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/31:
#0: ffffffff8e13bf20 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
#0: ffffffff8e13bf20 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
#0: ffffffff8e13bf20 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180 kernel/locking/lockdep.c:6770
3 locks held by kworker/u9:1/5156:
#0: ffff88804419a148 ((wq_completion)hci7){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3214 [inline]
#0: ffff88804419a148 ((wq_completion)hci7){+.+.}-{0:0}, at: process_scheduled_works+0x9b4/0x17b0 kernel/workqueue.c:3322
#1: ffffc9001023fbc0 ((work_completion)(&hdev->power_on)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3215 [inline]
#1: ffffc9001023fbc0 ((work_completion)(&hdev->power_on)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x17b0 kernel/workqueue.c:3322
#2: ffff888020f40dc0 (&hdev->req_lock){+.+.}-{4:4}, at: hci_dev_do_open net/bluetooth/hci_core.c:428 [inline]
#2: ffff888020f40dc0 (&hdev->req_lock){+.+.}-{4:4}, at: hci_power_on+0x1ac/0x680 net/bluetooth/hci_core.c:959
2 locks held by getty/5598:
#0: ffff8880303340a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
#1: ffffc9000331b2f0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x43e/0x1400 drivers/tty/n_tty.c:2222
1 lock held by syz.0.23/6171:
1 lock held by syz.2.43/6314:
1 lock held by syz.3.47/6351:
1 lock held by syz.4.49/6392:
1 lock held by syz.5.51/6429:
1 lock held by syz.6.54/6471:
1 lock held by dhcpcd/6476:
#0: ffff888077ab0e08 (&sb->s_type->i_mutex_key#11){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:869 [inline]
#0: ffff888077ab0e08 (&sb->s_type->i_mutex_key#11){+.+.}-{4:4}, at: __sock_release net/socket.c:648 [inline]
#0: ffff888077ab0e08 (&sb->s_type->i_mutex_key#11){+.+.}-{4:4}, at: sock_close+0x9b/0x240 net/socket.c:1439
2 locks held by dhcpcd/6477:
#0: ffff88805fcdc258 (sk_lock-AF_PACKET){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1667 [inline]
#0: ffff88805fcdc258 (sk_lock-AF_PACKET){+.+.}-{0:0}, at: packet_do_bind+0x32/0xcd0 net/packet/af_packet.c:3252
#1: ffffffff8e141a38 (rcu_state.exp_mutex){+.+.}-{4:4}, at: exp_funnel_lock kernel/rcu/tree_exp.h:343 [inline]
#1: ffffffff8e141a38 (rcu_state.exp_mutex){+.+.}-{4:4}, at: synchronize_rcu_expedited+0x3b9/0x730 kernel/rcu/tree_exp.h:967
1 lock held by dhcpcd/6478:
#0: ffff888044c5a258 (sk_lock-AF_PACKET){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1667 [inline]
#0: ffff888044c5a258 (sk_lock-AF_PACKET){+.+.}-{0:0}, at: packet_do_bind+0x32/0xcd0 net/packet/af_packet.c:3252
1 lock held by syz-executor/6480:
2 locks held by dhcpcd/6483:
#0: ffff888079892258 (sk_lock-AF_PACKET){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1667 [inline]
#0: ffff888079892258 (sk_lock-AF_PACKET){+.+.}-{0:0}, at: packet_do_bind+0x32/0xcd0 net/packet/af_packet.c:3252
#1: ffffffff8e141a38 (rcu_state.exp_mutex){+.+.}-{4:4}, at: exp_funnel_lock kernel/rcu/tree_exp.h:343 [inline]
#1: ffffffff8e141a38 (rcu_state.exp_mutex){+.+.}-{4:4}, at: synchronize_rcu_expedited+0x3b9/0x730 kernel/rcu/tree_exp.h:967

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

NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 31 Comm: khungtaskd Not tainted 6.16.0-rc3-next-20250627-syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
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:307 [inline]
watchdog+0xfee/0x1030 kernel/hung_task.c:470
kthread+0x711/0x8a0 kernel/kthread.c:463
ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 6314 Comm: syz.2.43 Not tainted 6.16.0-rc3-next-20250627-syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:arch_atomic_read arch/x86/include/asm/atomic.h:23 [inline]
RIP: 0010:raw_atomic_read include/linux/atomic/atomic-arch-fallback.h:457 [inline]
RIP: 0010:rcu_is_watching_curr_cpu include/linux/context_tracking.h:128 [inline]
RIP: 0010:rcu_is_watching+0x5a/0xb0 kernel/rcu/tree.c:751
Code: f0 48 c1 e8 03 42 80 3c 38 00 74 08 4c 89 f7 e8 7c 42 7d 00 48 c7 c3 18 4f a1 92 49 03 1e 48 89 d8 48 c1 e8 03 42 0f b6 04 38 <84> c0 75 34 8b 03 65 ff 0d 89 90 f9 10 74 11 83 e0 04 c1 e8 02 5b
RSP: 0018:ffffc900000079a8 EFLAGS: 00000802
RAX: 0000000000000000 RBX: ffff8880b8632f18 RCX: 1370d027c6756400
RDX: 0000000000000000 RSI: ffffffff8be31f60 RDI: ffffffff8be31f20
RBP: ffffffff81745448 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: fffffbfff33acaae R12: 0000000000000002
R13: ffffffff8e13bfe0 R14: ffffffff8dbb8cb0 R15: dffffc0000000000
FS: 00007f61f8d9d6c0(0000) GS:ffff888125c1e000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055a134a81660 CR3: 000000007fa0a000 CR4: 00000000003526f0
Call Trace:
<IRQ>
trace_lock_acquire include/trace/events/lock.h:24 [inline]
lock_acquire+0x5f/0x360 kernel/locking/lockdep.c:5834
rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
rcu_read_lock_sched include/linux/rcupdate.h:932 [inline]
pfn_valid include/linux/mmzone.h:2163 [inline]
__virt_addr_valid+0x1e5/0x5c0 arch/x86/mm/physaddr.c:65
kasan_addr_to_slab+0xf/0x90 mm/kasan/common.c:37
kasan_record_aux_stack+0xf/0xd0 mm/kasan/generic.c:533
insert_work+0x3d/0x330 kernel/workqueue.c:2187
__queue_work+0xbaf/0xfb0 kernel/workqueue.c:2346
call_timer_fn+0x17b/0x5f0 kernel/time/timer.c:1747
expire_timers kernel/time/timer.c:1793 [inline]
__run_timers kernel/time/timer.c:2372 [inline]
__run_timer_base+0x646/0x860 kernel/time/timer.c:2384
run_timer_base kernel/time/timer.c:2393 [inline]
run_timer_softirq+0xb7/0x180 kernel/time/timer.c:2403
handle_softirqs+0x286/0x870 kernel/softirq.c:579
__do_softirq kernel/softirq.c:613 [inline]
invoke_softirq kernel/softirq.c:453 [inline]
__irq_exit_rcu+0xca/0x1f0 kernel/softirq.c:680
irq_exit_rcu+0x9/0x30 kernel/softirq.c:696
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1050 [inline]
sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1050
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
RIP: 0010:lock_acquire+0x175/0x360 kernel/locking/lockdep.c:5875
Code: 00 00 00 00 9c 8f 44 24 30 f7 44 24 30 00 02 00 00 0f 85 cd 00 00 00 f7 44 24 08 00 02 00 00 74 01 fb 65 48 8b 05 5b 83 02 11 <48> 3b 44 24 58 0f 85 f2 00 00 00 48 83 c4 60 5b 41 5c 41 5d 41 5e
RSP: 0018:ffffc90003e6f980 EFLAGS: 00000206
RAX: 1370d027c6756400 RBX: 0000000000000000 RCX: 1370d027c6756400
RDX: 0000000000000000 RSI: ffffffff8db80736 RDI: ffffffff8be31f80
RBP: ffffffff84bc6539 R08: 0000000000000000 R09: ffffffff84bc6539
R10: ffffc90003e6fb00 R11: fffff520007cdf65 R12: 0000000000000000
R13: ffff88806038c0a8 R14: 0000000000000001 R15: 0000000000000246
__mutex_lock_common kernel/locking/mutex.c:602 [inline]
__mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
io_cqring_do_overflow_flush+0x19/0x30 io_uring/io_uring.c:665
io_cqring_wait io_uring/io_uring.c:2701 [inline]
__do_sys_io_uring_enter io_uring/io_uring.c:3508 [inline]
__se_sys_io_uring_enter+0x1fce/0x2b20 io_uring/io_uring.c:3403
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f61f7f8e929
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:00007f61f8d9d038 EFLAGS: 00000246 ORIG_RAX: 00000000000001aa
RAX: ffffffffffffffda RBX: 00007f61f81b5fa0 RCX: 00007f61f7f8e929
RDX: 0000000000001797 RSI: 0000000000000001 RDI: 0000000000000003
RBP: 00007f61f8010b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f61f81b5fa0 R15: 00007ffcfc501968
</TASK>


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

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.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[Jens Axboe]

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 886368cd2c40..887521656bca 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -660,11 +660,16 @@ static void io_cqring_overflow_kill(struct io_ring_ctx *ctx)
__io_cqring_overflow_flush(ctx, true);
}

-static void io_cqring_do_overflow_flush(struct io_ring_ctx *ctx)
+static int io_cqring_do_overflow_flush(struct io_ring_ctx *ctx)
{
- mutex_lock(&ctx->uring_lock);
+ int ret;
+
+ ret = mutex_lock_killable(&ctx->uring_lock);
+ if (unlikely(ret))
+ return ret;
__io_cqring_overflow_flush(ctx, false);
mutex_unlock(&ctx->uring_lock);
+ return 0;
}

/* must to be called somewhat shortly after putting a request */
@@ -2612,8 +2617,11 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events, u32 flags,
max(IO_LOCAL_TW_DEFAULT_MAX, min_events));
io_run_task_work();

- if (unlikely(test_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq)))
- io_cqring_do_overflow_flush(ctx);
+ if (unlikely(test_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq))) {
+ ret = io_cqring_do_overflow_flush(ctx);
+ if (ret)
+ return ret;
+ }
if (__io_cqring_events_user(ctx) >= min_events)
return 0;

@@ -2698,8 +2706,11 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events, u32 flags,
check_cq = READ_ONCE(ctx->check_cq);
if (unlikely(check_cq)) {
/* let the caller flush overflows, retry */
- if (check_cq & BIT(IO_CHECK_CQ_OVERFLOW_BIT))
- io_cqring_do_overflow_flush(ctx);
+ if (check_cq & BIT(IO_CHECK_CQ_OVERFLOW_BIT)) {
+ ret = io_cqring_do_overflow_flush(ctx);
+ if (ret)
+ break;
+ }
if (check_cq & BIT(IO_CHECK_CQ_DROPPED_BIT)) {
ret = -EBADR;
break;


--
Jens Axboe

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+c29db0...@syzkaller.appspotmail.com
Tested-by: syzbot+c29db0...@syzkaller.appspotmail.com

Tested on:

commit: 8d6c5833 Add linux-next specific files for 20250703
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=11670582580000
kernel config: https://syzkaller.appspot.com/x/.config?x=d7dc16394230c170
dashboard link: https://syzkaller.appspot.com/bug?extid=c29db0c6705a06cb65f2
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
patch: https://syzkaller.appspot.com/x/patch.diff?x=16837770580000

Note: testing is done by a robot and is best-effort only.

[Jens Axboe]

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git

--
Jens Axboe

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+c29db0...@syzkaller.appspotmail.com
Tested-by: syzbot+c29db0...@syzkaller.appspotmail.com

Tested on:

commit: 5f9df768 Merge branch 'mm-everything' of git://git.ker..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git --
console output: https://syzkaller.appspot.com/x/log.txt?x=137fc0f0580000
kernel config: https://syzkaller.appspot.com/x/.config?x=44a6ca1881a12208

dashboard link: https://syzkaller.appspot.com/bug?extid=c29db0c6705a06cb65f2
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7

Note: no patches were applied.

[Jens Axboe]

Pretty sure this was a fluke in linux-next, as it triggered around
that coredump rework, but then stopped triggering.

#syz invalid

--
Jens Axboe