INFO: task can't die in inet_twsk_purge

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    a9e26cb5 Add linux-next specific files for 20201208
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=161a9613500000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e259434a8eaf0206
dashboard link: https://syzkaller.appspot.com/bug?extid=4c1b0c5364346e7beafa
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=109cf703500000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1587c923500000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4c1b0c5364346e7beafa@xxxxxxxxxxxxxxxxxxxxxxxxx

INFO: task syz-executor343:8498 can't die for more than 143 seconds.
task:syz-executor343 state:R  running task     stack:25920 pid: 8498 ppid:  8495 flags:0x00004006
Call Trace:
 context_switch kernel/sched/core.c:4325 [inline]
 __schedule+0x8eb/0x21b0 kernel/sched/core.c:5076
 preempt_schedule_irq+0x4e/0x90 kernel/sched/core.c:5338
 rcu_read_unlock include/linux/rcupdate.h:694 [inline]
 inet_twsk_purge+0x57f/0x810 net/ipv4/inet_timewait_sock.c:299
INFO: task syz-executor343:8743 can't die for more than 145 seconds.
task:syz-executor343 state:R  running task     stack:25768 pid: 8743 ppid:  8494 flags:0x00004006
Call Trace:
 context_switch kernel/sched/core.c:4325 [inline]
 __schedule+0x8eb/0x21b0 kernel/sched/core.c:5076
 preempt_schedule_notrace+0x5b/0xd0 kernel/sched/core.c:5309
INFO: task syz-executor343:8744 can't die for more than 147 seconds.
task:syz-executor343 state:R  running task     stack:25784 pid: 8744 ppid:  8490 flags:0x00004006
Call Trace:
 context_switch kernel/sched/core.c:4325 [inline]
 __schedule+0x8eb/0x21b0 kernel/sched/core.c:5076
INFO: task syz-executor343:8745 can't die for more than 148 seconds.
task:syz-executor343 state:D stack:25864 pid: 8745 ppid:  8491 flags:0x00004006
Call Trace:
 context_switch kernel/sched/core.c:4325 [inline]
 __schedule+0x8eb/0x21b0 kernel/sched/core.c:5076
 schedule+0xcf/0x270 kernel/sched/core.c:5155
 synchronize_rcu_expedited+0x458/0x620 kernel/rcu/tree_exp.h:852
 synchronize_rcu+0xee/0x190 kernel/rcu/tree.c:3729
 ops_exit_list+0x10d/0x160 net/core/net_namespace.c:190
 setup_net+0x508/0x850 net/core/net_namespace.c:365
 copy_net_ns+0x376/0x7b0 net/core/net_namespace.c:483
 create_new_namespaces+0x3f6/0xb20 kernel/nsproxy.c:110
 unshare_nsproxy_namespaces+0xbd/0x230 kernel/nsproxy.c:231
 ksys_unshare+0x445/0x8e0 kernel/fork.c:2958
 __do_sys_unshare kernel/fork.c:3026 [inline]
 __se_sys_unshare kernel/fork.c:3024 [inline]
 __x64_sys_unshare+0x2d/0x40 kernel/fork.c:3024
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x4414a9
RSP: 002b:00007ffd8be6e998 EFLAGS: 00000246 ORIG_RAX: 0000000000000110
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004414a9
RDX: 00000000004414a9 RSI: ffffffffffffffff RDI: 0000000040000000
RBP: 000000000007851d R08: 00000000000000c2 R09: 00000000000000c2
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004021a0
R13: 0000000000402230 R14: 0000000000000000 R15: 0000000000000000
INFO: task syz-executor343:8748 can't die for more than 151 seconds.
task:syz-executor343 state:R  running task     stack:25784 pid: 8748 ppid:  8493 flags:0x00004006
Call Trace:
 context_switch kernel/sched/core.c:4325 [inline]
 __schedule+0x8eb/0x21b0 kernel/sched/core.c:5076
 native_restore_fl arch/x86/include/asm/irqflags.h:41 [inline]
 arch_local_irq_restore arch/x86/include/asm/irqflags.h:84 [inline]
 lock_is_held_type+0xc2/0x100 kernel/locking/lockdep.c:5478


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