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BUG: KCSAN: data-race in rcu_gp_fqs_check_wake / rcu_note_context_switch

write to 0xffffffff85a7d1d0 of 8 bytes by task 7576 on cpu 0:
 rcu_preempt_ctxt_queue kernel/rcu/tree_plugin.h:223 [inline]
 rcu_note_context_switch+0x6f6/0x760 kernel/rcu/tree_plugin.h:315
 __schedule+0xa4/0x690 kernel/sched/core.c:4016
 preempt_schedule_common+0x37/0x90 kernel/sched/core.c:4226
 preempt_schedule+0x30/0x40 kernel/sched/core.c:4251
 ___preempt_schedule+0x16/0x20 arch/x86/entry/thunk_64.S:50
 __raw_spin_unlock_irq include/linux/spinlock_api_smp.h:169 [inline]
 _raw_spin_unlock_irq+0x74/0x80 kernel/locking/spinlock.c:199
 spin_unlock_irq include/linux/spinlock.h:388 [inline]
 start_flush_work kernel/workqueue.c:3000 [inline]
 __flush_work+0x216/0x390 kernel/workqueue.c:3039
 flush_work kernel/workqueue.c:3061 [inline]
 flush_delayed_work+0x8a/0xe0 kernel/workqueue.c:3185
 wb_shutdown+0x108/0x1e0 mm/backing-dev.c:363
 bdi_unregister+0xab/0x3a0 mm/backing-dev.c:1011
 release_bdi mm/backing-dev.c:1032 [inline]
 kref_put include/linux/kref.h:65 [inline]
 bdi_put+0x112/0x130 mm/backing-dev.c:1041
 generic_shutdown_super+0x219/0x260 fs/super.c:476
 kill_anon_super+0x2f/0x50 fs/super.c:1106
 v9fs_kill_super+0x38/0x70 fs/9p/vfs_super.c:219
 deactivate_locked_super+0x64/0xb0 fs/super.c:335
 deactivate_super fs/super.c:366 [inline]
 deactivate_super+0xca/0xe0 fs/super.c:362
 cleanup_mnt+0x27f/0x330 fs/namespace.c:1102
 __cleanup_mnt+0x1f/0x30 fs/namespace.c:1109
 task_work_run+0xf6/0x130 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x2b4/0x2c0 arch/x86/entry/common.c:163
 prepare_exit_to_usermode arch/x86/entry/common.c:194 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:274 [inline]
 do_syscall_64+0x353/0x370 arch/x86/entry/common.c:300
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffffffff85a7d1d0 of 8 bytes by task 10 on cpu 1:
 rcu_gp_fqs_check_wake kernel/rcu/tree.c:1584 [inline]
 rcu_gp_fqs_check_wake+0x93/0xd0 kernel/rcu/tree.c:1574
 rcu_gp_fqs_loop+0x36c/0x580 kernel/rcu/tree.c:1639
 rcu_gp_kthread+0x143/0x230 kernel/rcu/tree.c:1799
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 10 Comm: rcu_preempt Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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