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BUG: KCSAN: data-race in do_recvmmsg / sock_alloc_send_pskb

write to 0xffff888070d7c270 of 4 bytes by task 4584 on cpu 1:
 do_recvmmsg+0x46e/0x540 net/socket.c:2762
 __sys_recvmmsg+0x1f1/0x200 net/socket.c:2785
 __do_sys_recvmmsg net/socket.c:2808 [inline]
 __se_sys_recvmmsg net/socket.c:2801 [inline]
 __x64_sys_recvmmsg+0x82/0xb0 net/socket.c:2801
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888070d7c270 of 4 bytes by task 4580 on cpu 0:
 sock_error include/net/sock.h:2156 [inline]
 sock_alloc_send_pskb+0xb5/0x510 net/core/sock.c:2222
 sock_alloc_send_skb+0x37/0x50 net/core/sock.c:2259
 __ip_append_data.isra.0+0x110c/0x1ef0 net/ipv4/ip_output.c:1089
 ip_make_skb+0x18d/0x1e0 net/ipv4/ip_output.c:1626
 udp_sendmsg+0x1540/0x1930 net/ipv4/udp.c:1173
 inet_sendmsg+0x69/0x90 net/ipv4/af_inet.c:807
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg+0x98/0xc0 net/socket.c:672
 ____sys_sendmsg+0x207/0x4c0 net/socket.c:2343
 ___sys_sendmsg+0xb5/0x100 net/socket.c:2397
 __sys_sendmmsg+0x10e/0x310 net/socket.c:2487
 __do_sys_sendmmsg net/socket.c:2516 [inline]
 __se_sys_sendmmsg net/socket.c:2513 [inline]
 __x64_sys_sendmmsg+0x60/0x80 net/socket.c:2513
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 4580 Comm: syz-executor.0 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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