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BUG: KCSAN: data-race in do_nanosleep / prepare_signal

write to 0xffff888107bda02c of 4 bytes by task 20955 on cpu 1:
 freezer_count include/linux/freezer.h:121 [inline]
 freezable_schedule include/linux/freezer.h:173 [inline]
 do_nanosleep+0x121/0x3d0 kernel/time/hrtimer.c:1878
 hrtimer_nanosleep+0xfa/0x1c0 kernel/time/hrtimer.c:1931
 common_nsleep+0x69/0x80 kernel/time/posix-timers.c:1227
 __do_sys_clock_nanosleep kernel/time/posix-timers.c:1267 [inline]
 __se_sys_clock_nanosleep kernel/time/posix-timers.c:1245 [inline]
 __x64_sys_clock_nanosleep+0x1ee/0x220 kernel/time/posix-timers.c:1245
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888107bda02c of 4 bytes by task 8430 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+0x64/0x790 kernel/signal.c:1082
 send_signal+0x398/0x3e0 kernel/signal.c:1242
 do_send_sig_info+0x9b/0xe0 kernel/signal.c:1291
 group_send_sig_info kernel/signal.c:1414 [inline]
 kill_pid_info+0x7f/0x100 kernel/signal.c:1448
 kill_proc_info kernel/signal.c:1465 [inline]
 kill_something_info kernel/signal.c:1562 [inline]
 __do_sys_kill kernel/signal.c:3683 [inline]
 __se_sys_kill+0xd3/0x450 kernel/signal.c:3677
 __x64_sys_kill+0x2d/0x40 kernel/signal.c:3677
 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: 8430 Comm: syz-executor.1 Not tainted 5.11.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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