INFO: task syz-executor4:6281 blocked for more than 140 seconds. Not tainted 4.20.0 #166 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. syz-executor4 D17768 6281 1 0x80000004 Call Trace: context_switch kernel/sched/core.c:2831 [inline] __schedule+0x86c/0x1ed0 kernel/sched/core.c:3472 schedule+0xfe/0x460 kernel/sched/core.c:3516 schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3574 __mutex_lock_common kernel/locking/mutex.c:1002 [inline] __mutex_lock+0xbe7/0x1700 kernel/locking/mutex.c:1072 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087 acct_get kernel/acct.c:161 [inline] slow_acct_process kernel/acct.c:577 [inline] acct_process+0x48b/0x875 kernel/acct.c:605 do_exit+0x1b89/0x26d0 kernel/exit.c:857 do_group_exit+0x177/0x440 kernel/exit.c:970 get_signal+0x8b0/0x1980 kernel/signal.c:2517 do_signal+0x9c/0x21c0 arch/x86/kernel/signal.c:816 exit_to_usermode_loop+0x2e5/0x380 arch/x86/entry/common.c:162 prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline] syscall_return_slowpath arch/x86/entry/common.c:268 [inline] do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x41134a Code: f2 0f 58 d0 f2 0f 5c c8 48 f7 c6 ff ff 0f 00 7c 65 0f 57 c0 f2 48 0f 2a c3 f2 0f 59 c1 f2 0f 10 0d 3b 09 57 00 f2 0f 59 c8 f2 <0f> 58 d1 f2 0f 10 05 43 0a 57 00 f2 0f 5c d0 0f 57 c0 66 0f 2e d0 RSP: 002b:00007fffd5c68e38 EFLAGS: 00000246 ORIG_RAX: 000000000000003d RAX: fffffffffffffe00 RBX: 00000000012d699b RCX: 000000000041134a RDX: 0000000040000000 RSI: 00007fffd5c68e70 RDI: ffffffffffffffff RBP: 000000000000036d R08: 0000000000000001 R09: 0000000000000001 R10: 0000000000000000 R11: 0000000000000246 R12: 00000000012d6940 R13: 0000000000052f1e R14: 00000000000000d3 R15: 0000000000000004 Showing all locks held in the system: 1 lock held by khungtaskd/1019: #0: 00000000ec668f11 (rcu_read_lock){....}, at: debug_show_all_locks+0xd0/0x424 kernel/locking/lockdep.c:4379 1 lock held by rsyslogd/6018: #0: 0000000013d9c452 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0x1bb/0x200 fs/file.c:766 2 locks held by getty/6140: #0: 0000000059639af9 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353 #1: 0000000090c66847 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154 2 locks held by getty/6141: #0: 000000003267c340 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353 #1: 00000000596cc57b (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154 2 locks held by getty/6142: #0: 00000000db89ecec (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353 #1: 00000000d0ff07a1 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154 2 locks held by getty/6143: #0: 000000007cadbe9a (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353 #1: 00000000e9fd18f0 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154 2 locks held by getty/6144: #0: 0000000085dab17f (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353 #1: 000000005c40fcc8 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154 2 locks held by getty/6145: #0: 00000000303a1b72 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353 #1: 000000008c2bc9cb (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154 2 locks held by getty/6146: #0: 00000000d6f8aa9d (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353 #1: 00000000ff510006 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154 1 lock held by syz-executor4/6281: #0: 00000000b9d9ba7c (&acct->lock#2){+.+.}, at: acct_get kernel/acct.c:161 [inline] #0: 00000000b9d9ba7c (&acct->lock#2){+.+.}, at: slow_acct_process kernel/acct.c:577 [inline] #0: 00000000b9d9ba7c (&acct->lock#2){+.+.}, at: acct_process+0x48b/0x875 kernel/acct.c:605 2 locks held by syz-executor2/10460: #0: 0000000005c4d746 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353 #1: 00000000ca615552 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154 3 locks held by syz-executor4/15405: #0: 00000000b9d9ba7c (&acct->lock#2){+.+.}, at: acct_get kernel/acct.c:161 [inline] #0: 00000000b9d9ba7c (&acct->lock#2){+.+.}, at: slow_acct_process kernel/acct.c:577 [inline] #0: 00000000b9d9ba7c (&acct->lock#2){+.+.}, at: acct_process+0x48b/0x875 kernel/acct.c:605 #1: 000000000edb43a4 (sb_writers#4){.+.+}, at: file_start_write_trylock include/linux/fs.h:2817 [inline] #1: 000000000edb43a4 (sb_writers#4){.+.+}, at: do_acct_process+0x1338/0x1660 kernel/acct.c:517 #2: 000000001bb0b750 (&sb->s_type->i_mutex_key#9){++++}, at: inode_trylock include/linux/fs.h:777 [inline] #2: 000000001bb0b750 (&sb->s_type->i_mutex_key#9){++++}, at: ext4_file_write_iter+0x2a1/0x1420 fs/ext4/file.c:232 ============================================= NMI backtrace for cpu 0 CPU: 0 PID: 1019 Comm: khungtaskd Not tainted 4.20.0 #166 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x1d3/0x2c6 lib/dump_stack.c:113 nmi_cpu_backtrace.cold.4+0x63/0xa2 lib/nmi_backtrace.c:101 nmi_trigger_cpumask_backtrace+0x1c2/0x22c lib/nmi_backtrace.c:62 arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38 trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline] check_hung_uninterruptible_tasks kernel/hung_task.c:205 [inline] watchdog+0xb51/0x1060 kernel/hung_task.c:289 kthread+0x35a/0x440 kernel/kthread.c:246 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352 Sending NMI from CPU 0 to CPUs 1: NMI backtrace for cpu 1 skipped: idling at native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:57