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BUG: KCSAN: data-race in do_signal_stop / prepare_signal

write to 0xffff88800d6ef02c of 4 bytes by task 28096 on cpu 1:
 freezer_count include/linux/freezer.h:121 [inline]
 freezable_schedule include/linux/freezer.h:173 [inline]
 do_signal_stop+0x56f/0x6e0 kernel/signal.c:2396
 get_signal+0x65d/0x14e0 kernel/signal.c:2733
 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+0x11a/0x1b0 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

read to 0xffff88800d6ef02c 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+0x872/0xd80 kernel/signal.c:962
 send_sigqueue+0xea/0x430 kernel/signal.c:1861
 posix_timer_event kernel/time/posix-timers.c:354 [inline]
 posix_timer_fn+0xe8/0x210 kernel/time/posix-timers.c:380
 __run_hrtimer+0x163/0x460 kernel/time/hrtimer.c:1519
 __hrtimer_run_queues kernel/time/hrtimer.c:1583 [inline]
 hrtimer_interrupt+0x36e/0xa30 kernel/time/hrtimer.c:1645
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1085 [inline]
 __sysvec_apic_timer_interrupt+0x6f/0x200 arch/x86/kernel/apic/apic.c:1102
 asm_call_irq_on_stack+0xf/0x20
 __run_sysvec_on_irqstack arch/x86/include/asm/irq_stack.h:37 [inline]
 run_sysvec_on_irqstack_cond arch/x86/include/asm/irq_stack.h:89 [inline]
 sysvec_apic_timer_interrupt+0x52/0x90 arch/x86/kernel/apic/apic.c:1096
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:629
 __sanitizer_cov_trace_pc+0x51/0x60 kernel/kcov.c:203
 entry_to_node lib/radix-tree.c:393 [inline]
 radix_tree_load_root lib/radix-tree.c:394 [inline]
 idr_get_free+0xa9/0x5d0 lib/radix-tree.c:1484
 idr_alloc_u32 lib/idr.c:46 [inline]
 idr_alloc_cyclic+0xe3/0x2d0 lib/idr.c:125
 __kernfs_new_node+0xbd/0x360 fs/kernfs/dir.c:632
 kernfs_new_node+0x5b/0xd0 fs/kernfs/dir.c:688
 __kernfs_create_file+0x45/0x1a0 fs/kernfs/file.c:985
 sysfs_add_file_mode_ns+0x1c1/0x250 fs/sysfs/file.c:306
 create_files fs/sysfs/group.c:64 [inline]
 internal_create_group+0x2e4/0x850 fs/sysfs/group.c:149
 internal_create_groups fs/sysfs/group.c:189 [inline]
 sysfs_create_groups+0x3d/0xf0 fs/sysfs/group.c:215
 device_add_groups drivers/base/core.c:2204 [inline]
 device_add_attrs drivers/base/core.c:2363 [inline]
 device_add+0x6fe/0xe50 drivers/base/core.c:3060
 netdev_register_kobject+0xfd/0x230 net/core/net-sysfs.c:1939
 register_netdevice+0xbcf/0x1100 net/core/dev.c:10057
 register_netdev+0x37/0x50 net/core/dev.c:10182
 loopback_net_init+0x52/0xf0 drivers/net/loopback.c:216
 ops_init+0x1e7/0x230 net/core/net_namespace.c:152
 setup_net+0x12b/0x640 net/core/net_namespace.c:342
 copy_net_ns+0x2a9/0x450 net/core/net_namespace.c:483
 create_new_namespaces+0x231/0x560 kernel/nsproxy.c:110
 copy_namespaces+0x116/0x160 kernel/nsproxy.c:178
 copy_process+0x12cb/0x2e00 kernel/fork.c:2100
 kernel_clone+0x14b/0x690 kernel/fork.c:2462
 __do_sys_clone kernel/fork.c:2579 [inline]
 __se_sys_clone kernel/fork.c:2563 [inline]
 __x64_sys_clone+0xc8/0xf0 kernel/fork.c:2563
 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: 28141 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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