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BUG: KCSAN: data-race in allow_direct_reclaim / balance_pgdat

write to 0xffff88823fffa998 of 8 bytes by task 737 on cpu 0:
 balance_pgdat+0x995/0xc00 mm/vmscan.c:3921
 kswapd+0x1f3/0x300 mm/vmscan.c:4125
 kthread+0x1d0/0x1f0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff88823fffa998 of 8 bytes by task 1027 on cpu 1:
 allow_direct_reclaim+0x1d5/0x2e0 mm/vmscan.c:3315
 throttle_direct_reclaim mm/vmscan.c:3411 [inline]
 try_to_free_pages+0x444/0x820 mm/vmscan.c:3458
 __perform_reclaim mm/page_alloc.c:4430 [inline]
 __alloc_pages_direct_reclaim mm/page_alloc.c:4451 [inline]
 __alloc_pages_slowpath+0x550/0xb70 mm/page_alloc.c:4855
 __alloc_pages+0x25e/0x320 mm/page_alloc.c:5213
 alloc_pages+0x21d/0x310 mm/mempolicy.c:2272
 __page_cache_alloc+0x4d/0xf0 mm/filemap.c:1005
 page_cache_ra_unbounded+0x1ae/0x410 mm/readahead.c:215
 do_page_cache_ra+0xa7/0xc0 mm/readahead.c:267
 do_sync_mmap_readahead+0x32b/0x360 mm/filemap.c:2903
 filemap_fault+0x1c9/0x7b0 mm/filemap.c:2990
 ext4_filemap_fault+0x4b/0x60 fs/ext4/inode.c:6194
 __do_fault mm/memory.c:3678 [inline]
 do_read_fault mm/memory.c:3980 [inline]
 do_fault mm/memory.c:4108 [inline]
 handle_pte_fault mm/memory.c:4367 [inline]
 __handle_mm_fault mm/memory.c:4502 [inline]
 handle_mm_fault+0xe8d/0x1a70 mm/memory.c:4600
 do_user_addr_fault+0x60c/0xc00 arch/x86/mm/fault.c:1390
 handle_page_fault arch/x86/mm/fault.c:1475 [inline]
 exc_page_fault+0x94/0x230 arch/x86/mm/fault.c:1531
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:577

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1027 Comm: systemd-journal Tainted: G        W         5.13.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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