KCSAN: data-race in do_sys_poll / pollwake

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 6cf7ccba Merge tag 'riscv-for-linus-5.8-rc6' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12147707100000
kernel config: https://syzkaller.appspot.com/x/.config?x=570eb530a65cd98e
dashboard link: https://syzkaller.appspot.com/bug?extid=a5d15da12b55f807031f
compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project.git ca2dcbd030eadbf0aa9b660efe864ff08af6e18b)
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+a5d15d...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in do_sys_poll / pollwake

write to 0xffffc90002133c40 of 4 bytes by task 26178 on cpu 0:
__pollwake fs/select.c:197 [inline]
pollwake+0xa7/0xf0 fs/select.c:217
__wake_up_common+0xbc/0x130 kernel/sched/wait.c:93
__wake_up_common_lock kernel/sched/wait.c:123 [inline]
__wake_up+0x80/0xc0 kernel/sched/wait.c:142
unix_dgram_peer_wake_relay+0xd0/0xf0 net/unix/af_unix.c:373
__wake_up_common+0xbc/0x130 kernel/sched/wait.c:93
__wake_up_common_lock kernel/sched/wait.c:123 [inline]
__wake_up_sync_key+0x83/0xc0 kernel/sched/wait.c:190
unix_dgram_recvmsg+0x386/0x830 net/unix/af_unix.c:2135
____sys_recvmsg+0x15a/0x2e0 include/linux/uio.h:235
___sys_recvmsg net/socket.c:2617 [inline]
do_recvmmsg+0x35c/0xa30 net/socket.c:2715
__sys_recvmmsg net/socket.c:2794 [inline]
__do_sys_recvmmsg net/socket.c:2817 [inline]
__se_sys_recvmmsg net/socket.c:2810 [inline]
__x64_sys_recvmmsg+0xcc/0x150 net/socket.c:2810
do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffffc90002133c40 of 4 bytes by task 26183 on cpu 1:
poll_schedule_timeout fs/select.c:242 [inline]
do_poll fs/select.c:961 [inline]
do_sys_poll+0x9a6/0xbc0 fs/select.c:1011
__do_sys_ppoll fs/select.c:1111 [inline]
__se_sys_ppoll+0x169/0x1b0 fs/select.c:1091
__x64_sys_ppoll+0x63/0x70 fs/select.c:1091
do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 26183 Comm: syz-executor.3 Not tainted 5.8.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================


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