upstream test error: WARNING in ep_scan_ready_list

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    3950e975 Merge branch 'exec-linus' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13be87cc900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c2b75627f23a2ff9
dashboard link: https://syzkaller.appspot.com/bug?extid=d99fcdc44745d2f54a57
compiler:       clang version 11.0.0 (https://github.com/llvm/llvm-project.git ca2dcbd030eadbf0aa9b660efe864ff08af6e18b)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d99fcdc44745d2f54a57@xxxxxxxxxxxxxxxxxxxxxxxxx

------------[ cut here ]------------
WARNING: CPU: 1 PID: 1 at fs/eventpoll.c:688 ep_scan_ready_list+0x9f/0x470 fs/eventpoll.c:688
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 1 Comm: systemd Not tainted 5.8.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x16e/0x25d lib/dump_stack.c:118
 panic+0x20c/0x69a kernel/panic.c:231
 __warn+0x211/0x240 kernel/panic.c:600
 report_bug+0x153/0x1d0 lib/bug.c:198
 handle_bug+0x4d/0x90 arch/x86/kernel/traps.c:235
 exc_invalid_op+0x16/0x70 arch/x86/kernel/traps.c:255
 asm_exc_invalid_op+0x12/0x20 arch/x86/include/asm/idtentry.h:547
RIP: 0010:ep_scan_ready_list+0x9f/0x470 fs/eventpoll.c:688
Code: 37 d4 c6 ff 85 db 74 1d e8 1e d0 c6 ff 40 84 ed 75 0c eb 1d e8 12 d0 c6 ff 40 84 ed 74 13 e8 08 d0 c6 ff eb 1c e8 01 d0 c6 ff <0f> 0b 40 84 ed 75 ed e8 f5 cf c6 ff 4c 89 f7 44 89 fe e8 1a 8b a5
RSP: 0000:ffffc90000c73dc8 EFLAGS: 00010293
RAX: ffffffff81853bff RBX: 0000000000000000 RCX: ffff88812b766040
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffffffff81853bd9 R09: 0000ffff88619eb7
R10: 0000ffffffffffff R11: 0000000000000000 R12: 0000000000000000
R13: ffffc90000c73de8 R14: ffff8881297af600 R15: 0000000000000000
 ep_send_events fs/eventpoll.c:1788 [inline]
 ep_poll fs/eventpoll.c:1944 [inline]
 do_epoll_wait+0x55c/0x920 fs/eventpoll.c:2333
 __do_sys_epoll_wait fs/eventpoll.c:2343 [inline]
 __se_sys_epoll_wait fs/eventpoll.c:2340 [inline]
 __x64_sys_epoll_wait+0x4d/0x60 fs/eventpoll.c:2340
 do_syscall_64+0x6a/0xe0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7f310b8db303
Code: 49 89 ca b8 e8 00 00 00 0f 05 48 3d 01 f0 ff ff 73 34 c3 48 83 ec 08 e8 0b c2 00 00 48 89 04 24 49 89 ca b8 e8 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 51 c2 00 00 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:00007ffdc7ffa4c0 EFLAGS: 00000293 ORIG_RAX: 00000000000000e8
RAX: ffffffffffffffda RBX: 000055e909e78f50 RCX: 00007f310b8db303
RDX: 0000000000000025 RSI: 00007ffdc7ffa4d0 RDI: 0000000000000004
RBP: 00007ffdc7ffa790 R08: 846474467368a395 R09: 00000000000061c0
R10: 00000000ffffffff R11: 0000000000000293 R12: 00007ffdc7ffa4d0
R13: 0000000000000001 R14: ffffffffffffffff R15: 0000000000000002
Kernel Offset: disabled
Rebooting in 86400 seconds..


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