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

[Jens Axboe <axboe@kernel.dk>]

On 7/2/25 9:52 AM, syzbot wrote:
> 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+c29db0c6705a06cb65f2@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 syzkaller@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


#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