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BUG: KCSAN: data-race in do_signal_stop / prepare_signal

read to 0xffff888121176024 of 4 bytes by interrupt on cpu 0:
 sig_task_ignored kernel/signal.c:94 [inline]
 sig_ignored kernel/signal.c:119 [inline]
 prepare_signal+0x1f5/0x7a0 kernel/signal.c:956
 send_sigqueue+0xc1/0x4b0 kernel/signal.c:1859
 posix_timer_event kernel/time/posix-timers.c:328 [inline]
 posix_timer_fn+0x10d/0x230 kernel/time/posix-timers.c:354
 __run_hrtimer kernel/time/hrtimer.c:1517 [inline]
 __hrtimer_run_queues+0x274/0x5f0 kernel/time/hrtimer.c:1579
 hrtimer_interrupt+0x22a/0x480 kernel/time/hrtimer.c:1641
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1110 [inline]
 smp_apic_timer_interrupt+0xdc/0x280 arch/x86/kernel/apic/apic.c:1135
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829
 __sanitizer_cov_trace_pc+0x48/0x50 kernel/kcov.c:194
 sctp_association_free+0x183/0x480 net/sctp/associola.c:363
 sctp_cmd_delete_tcb net/sctp/sm_sideeffect.c:934 [inline]
 sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1322 [inline]
 sctp_side_effects net/sctp/sm_sideeffect.c:1189 [inline]
 sctp_do_sm+0x277f/0x2f10 net/sctp/sm_sideeffect.c:1160
 sctp_assoc_bh_rcv+0x2d7/0x460 net/sctp/associola.c:1045
 sctp_inq_push+0x107/0x1a0 net/sctp/inqueue.c:80
 sctp_backlog_rcv+0x112/0x7d0 net/sctp/input.c:344
 sk_backlog_rcv include/net/sock.h:949 [inline]
 __release_sock+0x135/0x1e0 net/core/sock.c:2437
 release_sock+0x61/0x160 net/core/sock.c:2953
 sctp_connect net/sctp/socket.c:4897 [inline]
 sctp_inet_connect+0xe7/0x120 net/sctp/socket.c:4910
 __sys_connect_file+0xf4/0x100 net/socket.c:1844
 __sys_connect+0x121/0x150 net/socket.c:1861
 __do_sys_connect net/socket.c:1872 [inline]
 __se_sys_connect net/socket.c:1869 [inline]
 __x64_sys_connect+0x4c/0x60 net/socket.c:1869
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff888121176024 of 4 bytes by task 12505 on cpu 1:
 freezer_count include/linux/freezer.h:121 [inline]
 freezable_schedule include/linux/freezer.h:173 [inline]
 do_signal_stop+0x204/0x500 kernel/signal.c:2390
 get_signal+0x61b/0x1320 kernel/signal.c:2694
 do_signal+0x2f/0x6c0 arch/x86/kernel/signal.c:815
 exit_to_usermode_loop+0x250/0x2c0 arch/x86/entry/common.c:160
 prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:278 [inline]
 do_syscall_64+0x384/0x3a0 arch/x86/entry/common.c:304
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 12505 Comm: syz-executor.0 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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