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BUG: KCSAN: data-race in rds_cmsg_rdma_args / rds_cmsg_rdma_args

write to 0xffff888101be6500 of 8 bytes by task 5435 on cpu 0:
 rds_cmsg_rdma_args+0x63b/0xbf0 net/rds/rdma.c:715
 rds_cmsg_send+0x24a/0x3c0 net/rds/send.c:1004
 rds_sendmsg+0xc74/0x1400 net/rds/send.c:1314
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg+0x140/0x180 net/socket.c:745
 ____sys_sendmsg+0x312/0x410 net/socket.c:2584
 ___sys_sendmsg net/socket.c:2638 [inline]
 __sys_sendmsg+0x1e9/0x280 net/socket.c:2667
 __do_sys_sendmsg net/socket.c:2676 [inline]
 __se_sys_sendmsg net/socket.c:2674 [inline]
 __x64_sys_sendmsg+0x46/0x50 net/socket.c:2674
 x64_sys_call+0xae9/0x2d30 arch/x86/include/generated/asm/syscalls_64.h:47
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x1d0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

write to 0xffff888101be6500 of 8 bytes by task 5434 on cpu 1:
 rds_cmsg_rdma_args+0x63b/0xbf0 net/rds/rdma.c:715
 rds_cmsg_send+0x24a/0x3c0 net/rds/send.c:1004
 rds_sendmsg+0xc74/0x1400 net/rds/send.c:1314
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg+0x140/0x180 net/socket.c:745
 ____sys_sendmsg+0x312/0x410 net/socket.c:2584
 ___sys_sendmsg net/socket.c:2638 [inline]
 __sys_sendmsg+0x1e9/0x280 net/socket.c:2667
 __do_sys_sendmsg net/socket.c:2676 [inline]
 __se_sys_sendmsg net/socket.c:2674 [inline]
 __x64_sys_sendmsg+0x46/0x50 net/socket.c:2674
 x64_sys_call+0xae9/0x2d30 arch/x86/include/generated/asm/syscalls_64.h:47
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x1d0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000000 -> 0x0000000020000180

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 5434 Comm: syz-executor.4 Not tainted 6.9.0-rc3-syzkaller-00355-g7efd0a74039f #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
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rdma_op ffff888118b9d980 conn xmit_rdma 0000000000000000