KCSAN: data-race in do_epoll_ctl / do_epoll_ctl

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 4d02da97 Merge tag 'net-5.10-rc5' of git://git.kernel.org/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=166396e5500000
kernel config: https://syzkaller.appspot.com/x/.config?x=73fc125ff8990ab9
dashboard link: https://syzkaller.appspot.com/bug?extid=60e80f7ef1c268ce31a5
compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project.git 913f6005669cfb590c99865a90bc51ed0983d09d)
CC: [linux-...@vger.kernel.org linux-...@vger.kernel.org vi...@zeniv.linux.org.uk]

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: syzbot+60e80f...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in do_epoll_ctl / do_epoll_ctl

read-write to 0xffffffff883159e8 of 8 bytes by task 12917 on cpu 1:
do_epoll_ctl+0x41a/0x1c10 fs/eventpoll.c:2191
__do_sys_epoll_ctl fs/eventpoll.c:2281 [inline]
__se_sys_epoll_ctl fs/eventpoll.c:2272 [inline]
__x64_sys_epoll_ctl+0xb3/0xe0 fs/eventpoll.c:2272
do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffffffff883159e8 of 8 bytes by task 12916 on cpu 0:
do_epoll_ctl+0x367/0x1c10 fs/eventpoll.c:2185
__do_sys_epoll_ctl fs/eventpoll.c:2281 [inline]
__se_sys_epoll_ctl fs/eventpoll.c:2272 [inline]
__x64_sys_epoll_ctl+0xb3/0xe0 fs/eventpoll.c:2272
do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 12916 Comm: systemd-udevd Not tainted 5.10.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 12916 Comm: systemd-udevd Not tainted 5.10.0-rc4-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+0x116/0x15d lib/dump_stack.c:118
panic+0x1e7/0x5fa kernel/panic.c:231
kcsan_report+0x67b/0x680 kernel/kcsan/report.c:634
kcsan_setup_watchpoint+0x46a/0x4d0 kernel/kcsan/core.c:568
do_epoll_ctl+0x367/0x1c10 fs/eventpoll.c:2185
__do_sys_epoll_ctl fs/eventpoll.c:2281 [inline]
__se_sys_epoll_ctl fs/eventpoll.c:2272 [inline]
__x64_sys_epoll_ctl+0xb3/0xe0 fs/eventpoll.c:2272
do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7f4c9156b2aa
Code: 48 8b 0d f1 fb 2a 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 49 89 ca b8 e9 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d be fb 2a 00 f7 d8 64 89 01 48
RSP: 002b:00007ffc55baaab8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e9
RAX: ffffffffffffffda RBX: 00007ffc55baabb0 RCX: 00007f4c9156b2aa
RDX: 000000000000000e RSI: 0000000000000001 RDI: 0000000000000004
RBP: 0000563a0bb07028 R08: 0000000000000020 R09: 0000000000000018
R10: 00007ffc55baab64 R11: 0000000000000246 R12: 0000563a0bb07010
R13: 0000563a0bb080c0 R14: 0000000000000003 R15: 000000000000000e
Kernel Offset: disabled
Rebooting in 86400 seconds..


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.