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BUG: KCSAN: data-race in __lru_cache_add / lru_add_drain_all

read to 0xffff88812bf27620 of 1 bytes by task 11474 on cpu 0:
 lru_add_drain_all+0xf5/0x350 mm/swap.c:728
 invalidate_bdev+0x6e/0x90 fs/block_dev.c:97
 open_ctree+0x174c/0x3ce2 fs/btrfs/disk-io.c:2796
 btrfs_fill_super fs/btrfs/super.c:1213 [inline]
 btrfs_mount_root+0x8c7/0xb00 fs/btrfs/super.c:1561
 legacy_get_tree+0x7e/0xf0 fs/fs_context.c:647
 vfs_get_tree+0x56/0x1a0 fs/super.c:1545
 fc_mount+0x20/0x80 fs/namespace.c:962
 vfs_kern_mount.part.0+0xe6/0xf0 fs/namespace.c:992
 vfs_kern_mount+0x49/0x70 fs/namespace.c:979
 btrfs_mount+0x250/0xf37 fs/btrfs/super.c:1621
 legacy_get_tree+0x7e/0xf0 fs/fs_context.c:647
 vfs_get_tree+0x56/0x1a0 fs/super.c:1545
 do_new_mount fs/namespace.c:2823 [inline]
 do_mount+0x1049/0x1560 fs/namespace.c:3143
 ksys_mount+0xe8/0x160 fs/namespace.c:3352
 __do_sys_mount fs/namespace.c:3366 [inline]
 __se_sys_mount fs/namespace.c:3363 [inline]
 __x64_sys_mount+0x70/0x90 fs/namespace.c:3363
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff88812bf27620 of 1 bytes by task 11498 on cpu 1:
 pagevec_add include/linux/pagevec.h:81 [inline]
 __lru_cache_add+0xbf/0x1d0 mm/swap.c:405
 lru_cache_add mm/swap.c:442 [inline]
 lru_cache_add_active_or_unevictable+0xb6/0x1f0 mm/swap.c:472
 wp_page_copy+0x820/0x1120 mm/memory.c:2369
 do_wp_page+0x192/0x11f0 mm/memory.c:2628
 handle_pte_fault mm/memory.c:3865 [inline]
 __handle_mm_fault+0x1ab1/0x2c70 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 11498 Comm: blkid Not tainted 5.4.0-rc6+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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