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BUG: KCSAN: data-race in kernel_clone / prepare_signal

read-write to 0xffff88803541f02c of 4 bytes by task 19543 on cpu 1:
 freezer_count include/linux/freezer.h:121 [inline]
 wait_for_vfork_done kernel/fork.c:1265 [inline]
 kernel_clone+0x2d3/0x680 kernel/fork.c:2495
 __do_sys_clone kernel/fork.c:2581 [inline]
 __se_sys_clone kernel/fork.c:2565 [inline]
 __x64_sys_clone+0xc8/0xf0 kernel/fork.c:2565
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88803541f02c of 4 bytes by task 19566 on cpu 0:
 sig_task_ignored kernel/signal.c:94 [inline]
 sig_ignored kernel/signal.c:119 [inline]
 prepare_signal+0x872/0xd80 kernel/signal.c:962
 __send_signal+0x64/0x780 kernel/signal.c:1082
 send_signal+0x39f/0x3d0 kernel/signal.c:1242
 __group_send_sig_info kernel/signal.c:1281 [inline]
 do_notify_parent_cldstop+0x23a/0x290 kernel/signal.c:2068
 do_signal_stop+0x502/0x6b0 kernel/signal.c:2390
 get_signal+0x645/0x1440 kernel/signal.c:2730
 arch_do_signal_or_restart+0x2a/0x270 arch/x86/kernel/signal.c:811
 handle_signal_work kernel/entry/common.c:147 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:171 [inline]
 exit_to_user_mode_prepare+0x109/0x1a0 kernel/entry/common.c:201
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:302
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 19566 Comm: syz-executor.0 Not tainted 5.10.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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