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BUG: KCSAN: data-race in rds_cong_map_updated / rds_recvmsg

write to 0xffff8880b0a44ca8 of 8 bytes by task 2941 on cpu 0:
 rds_notify_cong net/rds/recv.c:530 [inline]
 rds_recvmsg+0x9b9/0x1260 net/rds/recv.c:662
 ____sys_recvmsg+0x15a/0x2e0 include/linux/uio.h:234
 ___sys_recvmsg net/socket.c:2618 [inline]
 do_recvmmsg+0x35c/0xa30 net/socket.c:2716
 __sys_recvmmsg net/socket.c:2795 [inline]
 __do_sys_recvmmsg net/socket.c:2818 [inline]
 __se_sys_recvmmsg net/socket.c:2811 [inline]
 __x64_sys_recvmmsg+0xcc/0x150 net/socket.c:2811
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880b0a44ca8 of 8 bytes by task 25933 on cpu 1:
 rds_cong_map_updated+0x200/0x2a0 net/rds/cong.c:274
 rds_loop_xmit+0xff/0x160 net/rds/loop.c:85
 rds_send_xmit+0xbca/0x1510 net/rds/send.c:367
 rds_send_worker+0x43/0x200 net/rds/threads.c:200
 process_one_work+0x3e1/0x9a0 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x20d/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 25933 Comm: kworker/u4:3 Not tainted 5.9.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: krdsd rds_send_worker
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