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BUG: KCSAN: data-race in kcm_rcv_strparser / kcm_rfree

write to 0xffff888100f8bb78 of 1 bytes by task 772 on cpu 1:
 reserve_rx_kcm net/kcm/kcmsock.c:282 [inline]
 kcm_rcv_strparser+0x250/0x3a0 net/kcm/kcmsock.c:362
 __strp_recv+0x65d/0xde0 net/strparser/strparser.c:309
 strp_recv+0x6d/0x80 net/strparser/strparser.c:343
 tcp_read_sock+0x287/0xb90 net/ipv4/tcp.c:1662
 strp_read_sock net/strparser/strparser.c:366 [inline]
 do_strp_work net/strparser/strparser.c:414 [inline]
 strp_work+0xd9/0x170 net/strparser/strparser.c:423
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2275
 worker_thread+0x635/0xb90 kernel/workqueue.c:2421
 kthread+0x1fd/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffff888100f8bb78 of 1 bytes by task 10584 on cpu 0:
 kcm_rfree+0xb7/0x170 net/kcm/kcmsock.c:180
 skb_release_head_state+0xb3/0x170 net/core/skbuff.c:656
 skb_release_all net/core/skbuff.c:667 [inline]
 __kfree_skb+0x14/0x150 net/core/skbuff.c:683
 kfree_skb+0x50/0x170 net/core/skbuff.c:701
 kcm_recvmsg+0x3c0/0x440 net/kcm/kcmsock.c:1160
 ____sys_recvmsg+0x15d/0x310 include/linux/uio.h:234
 ___sys_recvmsg net/socket.c:2610 [inline]
 do_recvmmsg+0x4b3/0x990 net/socket.c:2710
 __sys_recvmmsg net/socket.c:2789 [inline]
 __do_sys_recvmmsg net/socket.c:2812 [inline]
 __se_sys_recvmmsg net/socket.c:2805 [inline]
 __x64_sys_recvmmsg+0xcf/0x150 net/socket.c:2805
 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: 10584 Comm: syz-executor.0 Not tainted 5.11.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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