syzbot

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dst_release underflow
WARNING: CPU: 1 PID: 10 at net/core/dst.c:173 dst_release net/core/dst.c:173 [inline]
WARNING: CPU: 1 PID: 10 at net/core/dst.c:173 dst_release+0xd2/0xe0 net/core/dst.c:167
Modules linked in:
CPU: 1 PID: 10 Comm: kworker/u4:1 Not tainted 5.14.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: netns cleanup_net
RIP: 0010:dst_release net/core/dst.c:173 [inline]
RIP: 0010:dst_release+0xd2/0xe0 net/core/dst.c:167
Code: 89 c3 89 c6 e8 2f d7 55 fa 85 db 74 a4 e9 a0 cb 0e 02 e8 71 ce 55 fa 48 c7 c7 00 f8 8a 8a c6 05 db b5 39 06 01 e8 c5 fe d0 01 <0f> 0b eb c6 66 2e 0f 1f 84 00 00 00 00 00 41 56 41 55 41 54 55 48
RSP: 0018:ffffc90000f0f9e8 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffff888012216280 RSI: ffffffff815cfbd8 RDI: fffff520001e1f2f
RBP: ffffe8ffffcc8ac0 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffff815c994e R11: 0000000000000000 R12: ffff88802d43ad00
R13: 00000000ffffffff R14: 0000000000000007 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000001886708 CR3: 0000000031629000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 dst_cache_destroy net/core/dst_cache.c:160 [inline]
 dst_cache_destroy+0xcb/0x190 net/core/dst_cache.c:152
 ip_tunnel_dev_free+0x21/0x60 net/ipv4/ip_tunnel.c:1011
 netdev_run_todo+0x6b4/0xa80 net/core/dev.c:10589
 ip_tunnel_delete_nets+0x3a4/0x5b0 net/ipv4/ip_tunnel.c:1124
 ops_exit_list+0x10d/0x160 net/core/net_namespace.c:171
 cleanup_net+0x4ea/0xb00 net/core/net_namespace.c:591
 process_one_work+0x9bf/0x16b0 kernel/workqueue.c:2297
 worker_thread+0x658/0x11f0 kernel/workqueue.c:2444
 kthread+0x3e5/0x4d0 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295