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BUG: KCSAN: data-race in __rcu_read_unlock / sync_rcu_exp_select_node_cpus

read to 0xffffffff85a7d458 of 8 bytes by task 15476 on cpu 1:
 rcu_read_unlock_special kernel/rcu/tree_plugin.h:614 [inline]
 __rcu_read_unlock+0x1f6/0x3c0 kernel/rcu/tree_plugin.h:383
 rcu_read_unlock include/linux/rcupdate.h:652 [inline]
 filemap_map_pages+0x5b3/0x990 mm/filemap.c:2688
 do_fault_around mm/memory.c:3450 [inline]
 do_read_fault mm/memory.c:3484 [inline]
 do_fault mm/memory.c:3618 [inline]
 handle_pte_fault mm/memory.c:3849 [inline]
 __handle_mm_fault+0x2544/0x2c70 mm/memory.c:3973
 handle_mm_fault+0x21b/0x530 mm/memory.c:4010
 do_user_addr_fault arch/x86/mm/fault.c:1441 [inline]
 __do_page_fault+0x3fb/0x9e0 arch/x86/mm/fault.c:1506
 do_page_fault+0x54/0x233 arch/x86/mm/fault.c:1530
 page_fault+0x34/0x40 arch/x86/entry/entry_64.S:1202

write to 0xffffffff85a7d458 of 8 bytes by task 8189 on cpu 0:
 sync_rcu_exp_select_node_cpus+0x208/0x510 kernel/rcu/tree_exp.h:371
 sync_rcu_exp_select_cpus+0x30c/0x590 kernel/rcu/tree_exp.h:439
 rcu_exp_sel_wait_wake kernel/rcu/tree_exp.h:575 [inline]
 wait_rcu_exp_gp+0x25/0x40 kernel/rcu/tree_exp.h:589
 process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
 worker_thread+0xa0/0x800 kernel/workqueue.c:2415
 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: 0 PID: 8189 Comm: kworker/0:5 Not tainted 5.4.0-rc6+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: rcu_gp wait_rcu_exp_gp
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