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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 7989 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_irq+0x57/0x90 kernel/sched/core.c:4328
 restore_regs_and_return_to_kernel+0x0/0x25
 arch_local_irq_restore arch/x86/include/asm/paravirt.h:756 [inline]
 kcsan_setup_watchpoint+0x1d4/0x460 kernel/kcsan/core.c:436
 check_access kernel/kcsan/core.c:466 [inline]
 __tsan_read1 kernel/kcsan/core.c:593 [inline]
 __tsan_read1+0xc2/0x100 kernel/kcsan/core.c:593
 xas_start+0x160/0x230 lib/xarray.c:192
 xas_load+0x2a/0x100 lib/xarray.c:232
 find_get_entry+0xdd/0x330 mm/filemap.c:1533
 find_lock_entry+0x3f/0x1c0 mm/filemap.c:1584
 shmem_getpage_gfp+0x183/0x1390 mm/shmem.c:1770
 shmem_fault+0x114/0x3f0 mm/shmem.c:2065
 __do_fault+0xae/0x1f0 mm/memory.c:3092
 do_read_fault mm/memory.c:3489 [inline]
 do_fault mm/memory.c:3618 [inline]
 handle_pte_fault mm/memory.c:3849 [inline]
 __handle_mm_fault+0x1f90/0x2c70 mm/memory.c:3973
 handle_mm_fault+0x21b/0x530 mm/memory.c:4010
 faultin_page mm/gup.c:640 [inline]
 __get_user_pages+0x485/0x1160 mm/gup.c:845
 populate_vma_page_range+0xe6/0x100 mm/gup.c:1223
 __mm_populate+0x168/0x2a0 mm/gup.c:1271
 mm_populate include/linux/mm.h:2357 [inline]
 vm_mmap_pgoff+0x181/0x190 mm/util.c:501
 ksys_mmap_pgoff+0x99/0x420 mm/mmap.c:1629
 __do_sys_mmap arch/x86/kernel/sys_x86_64.c:100 [inline]
 __se_sys_mmap arch/x86/kernel/sys_x86_64.c:91 [inline]
 __x64_sys_mmap+0x2e/0x40 arch/x86/kernel/sys_x86_64.c:91
 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 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+0x1df/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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