Subject: WARNING: suspicious RCU usage in get_counters

From: syzbot <[email-masked]>
Date: Sun, 29 Nov 2020 02:58:23 -0800

Hello,

syzbot found the following issue on:

HEAD commit:    127c501a Merge tag '5.10-rc5-smb3-fixes' of git://git.samb..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17f4912d500000
kernel config:  https://syzkaller.appspot.com/x/.config?x=6d1e98d0b97781e4
dashboard link: https://syzkaller.appspot.com/bug?extid=5cfc290df4bbf069bc65
compiler:       gcc (GCC) 10.1.0-syz 20200507

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

=============================
WARNING: suspicious RCU usage
5.10.0-rc5-syzkaller #0 Not tainted
-----------------------------
kernel/sched/core.c:7270 Illegal context switch in RCU-sched 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.3/10331:
 #0: ffff8880459f8308 (&xt[i].mutex){+.+.}-{3:3}, at: xt_find_table_lock+0x41/0x540 net/netfilter/x_tables.c:1206

stack backtrace:
CPU: 3 PID: 10331 Comm: syz-executor.3 Not tainted 5.10.0-rc5-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:77 [inline]
 dump_stack+0x107/0x163 lib/dump_stack.c:118
 ___might_sleep+0x25d/0x2b0 kernel/sched/core.c:7270
 get_counters+0x2f5/0x520 net/ipv4/netfilter/ip_tables.c:765
 do_ipt_get_ctl+0x634/0x9d0 net/ipv4/netfilter/ip_tables.c:805
 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:3882
 __sys_getsockopt+0x219/0x4c0 net/socket.c:2173
 __do_sys_getsockopt net/socket.c:2188 [inline]
 __se_sys_getsockopt net/socket.c:2185 [inline]
 __x64_sys_getsockopt+0xba/0x150 net/socket.c:2185
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45ec3a
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:00007ffccbec9f78 EFLAGS: 00000212 ORIG_RAX: 0000000000000037
RAX: ffffffffffffffda RBX: 00007ffccbec9fb0 RCX: 000000000045ec3a
RDX: 0000000000000041 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 0000000000734000 R08: 00007ffccbec9fac R09: 0000000000004000
R10: 00007ffccbeca010 R11: 0000000000000212 R12: 00007ffccbeca010
R13: 0000000000000003 R14: 0000000000732bc0 R15: 0000000000000000

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