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BUG: KCSAN: data-race in kcm_rfree / unreserve_rx_kcm

write to 0xffff88809b4b13a0 of 8 bytes by task 3520 on cpu 0:
 unreserve_rx_kcm+0x72/0x1e0 net/kcm/kcmsock.c:312
 kcm_rcv_strparser+0x2d5/0x3d0 net/kcm/kcmsock.c:372
 __strp_recv+0x699/0xf00 net/strparser/strparser.c:309
 strp_recv+0x6d/0x80 net/strparser/strparser.c:343
 tcp_read_sock+0x290/0xb10 net/ipv4/tcp.c:1646
 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+0x3e1/0x9a0 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

read to 0xffff88809b4b13a0 of 8 bytes by task 14257 on cpu 1:
 kcm_rfree+0xee/0x180 net/kcm/kcmsock.c:180
 skb_release_head_state+0xb3/0x170 net/core/skbuff.c:651
 skb_release_all net/core/skbuff.c:662 [inline]
 __kfree_skb+0x14/0x150 net/core/skbuff.c:678
 kfree_skb+0x53/0x190 net/core/skbuff.c:696
 kcm_recvmsg+0x3c4/0x440 net/kcm/kcmsock.c:1160
 ____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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 14257 Comm: syz-executor.2 Not tainted 5.9.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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