WARNING: suspicious RCU usage in xt_obj_to

WARNING: suspicious RCU usage in xt_obj_to_user
Status: upstream: reported on 2021/01/01 00:49
Reported-by: syzbot+00399fa030c641ffc5ae@syzkaller.appspotmail.com
First crash: 108d, last: 108d

Sample crash report:

=============================
WARNING: suspicious RCU usage
5.10.0-syzkaller #0 Not tainted
-----------------------------
kernel/sched/core.c:7877 Illegal context switch in RCU-bh read-side critical section!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 0
1 lock held by syz-executor.0/9704:
 #0: ffff888013794458 (&xt[i].mutex){+.+.}-{3:3}, at: xt_find_table_lock+0x41/0x540 net/netfilter/x_tables.c:1206

stack backtrace:
CPU: 0 PID: 9704 Comm: syz-executor.0 Not tainted 5.10.0-syzkaller #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x107/0x163 lib/dump_stack.c:120
 ___might_sleep+0x229/0x2c0 kernel/sched/core.c:7877
 __might_fault+0x6e/0x180 mm/memory.c:5014
 xt_obj_to_user+0x31/0x110 net/netfilter/x_tables.c:277
 xt_target_to_user+0xa8/0x200 net/netfilter/x_tables.c:323
 copy_entries_to_user net/ipv4/netfilter/arp_tables.c:705 [inline]
 get_entries net/ipv4/netfilter/arp_tables.c:866 [inline]
 do_arpt_get_ctl+0x733/0x8f0 net/ipv4/netfilter/arp_tables.c:1450
 nf_getsockopt+0x72/0xd0 net/netfilter/nf_sockopt.c:116
 ip_getsockopt net/ipv4/ip_sockglue.c:1777 [inline]
 ip_getsockopt+0x164/0x1c0 net/ipv4/ip_sockglue.c:1756
 tcp_getsockopt+0x86/0xd0 net/ipv4/tcp.c:4141
 __sys_getsockopt+0x219/0x4c0 net/socket.c:2156
 __do_sys_getsockopt net/socket.c:2171 [inline]
 __se_sys_getsockopt net/socket.c:2168 [inline]
 __x64_sys_getsockopt+0xba/0x150 net/socket.c:2168
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45ef5a
Code: b8 34 01 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 cd 9f fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 49 89 ca b8 37 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 aa 9f fb ff c3 66 0f 1f 84 00 00 00 00 00
RSP: 002b:00007ffcf91ed728 EFLAGS: 00000212 ORIG_RAX: 0000000000000037
RAX: ffffffffffffffda RBX: 00007ffcf91ed790 RCX: 000000000045ef5a
RDX: 0000000000000061 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 0000000000000003 R08: 00007ffcf91ed73c R09: 000000000000000a
R10: 00007ffcf91ed790 R11: 0000000000000212 R12: 00007ffcf91ed73c
R13: 0000000000000000 R14: 0000000000000032 R15: 000000000003354d

Crashes (1):
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro	VM info	Title
ci-qemu-upstream	2020/12/28 00:44	upstream	f838f8d2	2242f77f	.config	log	report			info