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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 9061 on cpu 1:
 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_irq+0x57/0x90 kernel/sched/core.c:4328
 restore_regs_and_return_to_kernel+0x0/0x25
 __read_once_size+0x51/0xe0 include/linux/compiler.h:229
 arch_atomic_read arch/x86/include/asm/atomic.h:31 [inline]
 atomic_read include/asm-generic/atomic-instrumented.h:40 [inline]
 atomic_fetch_add_unless include/linux/atomic-fallback.h:1086 [inline]
 atomic_add_unless include/linux/atomic-fallback.h:1111 [inline]
 page_ref_add_unless include/linux/page_ref.h:157 [inline]
 __page_cache_add_speculative include/linux/pagemap.h:186 [inline]
 page_cache_get_speculative include/linux/pagemap.h:202 [inline]
 find_get_pages_range_tag+0x2dc/0x670 mm/filemap.c:1936
 pagevec_lookup_range_tag+0x45/0x70 mm/swap.c:1054
 mpage_prepare_extent_to_map+0x1e2/0x760 fs/ext4/inode.c:2645
 ext4_writepages+0xb2b/0x2300 fs/ext4/inode.c:2866
 do_writepages+0x6b/0x170 mm/page-writeback.c:2344
 __filemap_fdatawrite_range+0x1c5/0x230 mm/filemap.c:421
 generic_fadvise+0x4a0/0x4b0 mm/fadvise.c:115
 vfs_fadvise+0x92/0xa0 mm/fadvise.c:187
 ksys_fadvise64_64+0x61/0xa0 mm/fadvise.c:201
 __do_sys_fadvise64 mm/fadvise.c:216 [inline]
 __se_sys_fadvise64 mm/fadvise.c:214 [inline]
 __x64_sys_fadvise64+0x5e/0x80 mm/fadvise.c:214
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffffffff85a7d1d0 of 8 bytes by task 10 on cpu 0:
 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: 0 PID: 10 Comm: rcu_preempt Not tainted 5.4.0-rc7+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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