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BUG: KCSAN: data-race in kcm_rfree / unreserve_rx_kcm

write to 0xffff888106af6f20 of 8 bytes by task 281 on cpu 0:
 unreserve_rx_kcm+0x72/0x1e0 net/kcm/kcmsock.c:312
 kcm_rcv_strparser+0x2d3/0x3d0 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:1660
 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+0x616/0xa70 kernel/workqueue.c:2421
 kthread+0x20b/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff888106af6f20 of 8 bytes by task 12273 on cpu 1:
 kcm_rfree+0xee/0x180 net/kcm/kcmsock.c:180
 skb_release_head_state+0xb3/0x170 net/core/skbuff.c:712
 skb_release_all net/core/skbuff.c:723 [inline]
 __kfree_skb+0x14/0x150 net/core/skbuff.c:739
 kfree_skb+0x50/0x170 net/core/skbuff.c:757
 kcm_recvmsg+0x3f1/0x470 net/kcm/kcmsock.c:1160
 ____sys_recvmsg+0x15d/0x310 include/linux/uio.h:234
 ___sys_recvmsg net/socket.c:2611 [inline]
 do_recvmmsg+0x34c/0x9e0 net/socket.c:2705
 __sys_recvmmsg net/socket.c:2784 [inline]
 __do_sys_recvmmsg net/socket.c:2807 [inline]
 __se_sys_recvmmsg net/socket.c:2800 [inline]
 __x64_sys_recvmmsg+0xcf/0x150 net/socket.c:2800
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 12273 Comm: syz-executor.5 Not tainted 5.12.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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