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BUG: KCSAN: data-race in balance_pgdat / shrink_node

write to 0xffff88813fffb698 of 8 bytes by task 2189 on cpu 1:
 balance_pgdat+0x9d5/0xc40 mm/vmscan.c:3732
 kswapd+0x1de/0x310 mm/vmscan.c:3936
 kthread+0x1fd/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffff88813fffb698 of 8 bytes by task 8425 on cpu 0:
 shrink_node+0x831/0x1210 mm/vmscan.c:2762
 shrink_zones+0x29f/0x470 mm/vmscan.c:2981
 do_try_to_free_pages+0x193/0x6f0 mm/vmscan.c:3036
 try_to_free_pages+0x399/0x870 mm/vmscan.c:3275
 __perform_reclaim mm/page_alloc.c:4376 [inline]
 __alloc_pages_direct_reclaim mm/page_alloc.c:4397 [inline]
 __alloc_pages_slowpath+0x52f/0x9c0 mm/page_alloc.c:4801
 __alloc_pages_nodemask+0x269/0x350 mm/page_alloc.c:5011
 alloc_pages_current+0x21d/0x310 mm/mempolicy.c:2267
 alloc_pages include/linux/gfp.h:547 [inline]
 __page_cache_alloc+0x4d/0xf0 mm/filemap.c:977
 pagecache_get_page+0x554/0x980 mm/filemap.c:1837
 filemap_fault+0x1ef/0xbf0 mm/filemap.c:2823
 ext4_filemap_fault+0x4b/0x60 fs/ext4/inode.c:6201
 __do_fault mm/memory.c:3625 [inline]
 do_read_fault+0x403/0x760 mm/memory.c:4019
 do_fault mm/memory.c:4147 [inline]
 handle_pte_fault mm/memory.c:4387 [inline]
 __handle_mm_fault mm/memory.c:4522 [inline]
 handle_mm_fault+0xff1/0x17b0 mm/memory.c:4620
 do_user_addr_fault+0x433/0x830 arch/x86/mm/fault.c:1393
 handle_page_fault arch/x86/mm/fault.c:1450 [inline]
 exc_page_fault+0x94/0x2a0 arch/x86/mm/fault.c:1506
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:580

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8425 Comm: syz-fuzzer Not tainted 5.11.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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