[ 1221.689686] rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks: { P387 } 1202612 jiffies s: 625 root: 0x0/T
[ 1221.689962] rcu: blocking rcu_node structures (internal RCU debug):
[ 1237.184651] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
[ 1237.184851] rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-3): P387/1:b..l
[ 1237.184903] rcu: 	(detected by 3, t=1218104 jiffies, g=945, q=258 ncpus=4)
[ 1237.184946] task:grep            state:D stack:12736 pid:387   tgid:387   ppid:1      task_flags:0x40010c flags:0x00004002
[ 1237.185033] Call Trace:
[ 1237.185055]  <TASK>
[ 1237.185082]  __schedule+0x4e3/0xb40
[ 1237.185130]  schedule+0x27/0xd0
[ 1237.185162]  synchronize_rcu_expedited+0x17c/0x2f0
[ 1237.185210]  ? __pfx_autoremove_wake_function+0x10/0x10
[ 1237.185257]  ? __pfx_wait_rcu_exp_gp+0x10/0x10
[ 1237.185297]  namespace_unlock+0x20e/0x2e0
[ 1237.185334]  put_mnt_ns+0x68/0x80
[ 1237.185378]  free_nsproxy+0x16/0x190
[ 1237.185412]  do_exit+0x267/0xae0
[ 1237.185449]  ? ksys_read+0x65/0xe0
[ 1237.185486]  make_task_dead+0x7d/0x160
[ 1237.185513]  rewind_stack_and_make_dead+0x16/0x20
[ 1237.185561] RIP: 0033:0x7f08bad46292
[ 1237.185594] RSP: 002b:00007ffda3bda808 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
[ 1237.185649] RAX: ffffffffffffffda RBX: 0000000000018000 RCX: 00007f08bad46292
[ 1237.185707] RDX: 0000000000018000 RSI: 0000558cde187000 RDI: 0000000000000005
[ 1237.185758] RBP: 0000558cde187000 R08: 0000000000000003 R09: 0000000000000000
[ 1237.185809] R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffda3bda8e0
[ 1237.185860] R13: 0000000000000005 R14: 0000000000001000 R15: 0000000000000005
[ 1237.185912]  </TASK>