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BUG: KCSAN: data-race in __lru_cache_add / lru_add_drain_all

write to 0xffff88812c029b60 of 1 bytes by task 6570 on cpu 0:
 pagevec_add include/linux/pagevec.h:81 [inline]
 __lru_cache_add+0xb8/0x1c0 mm/swap.c:410
 lru_cache_add_anon+0x98/0x120 mm/swap.c:423
 shmem_getpage_gfp+0x4d4/0x14c0 mm/shmem.c:1885
 shmem_getpage mm/shmem.c:154 [inline]
 shmem_file_read_iter+0x221/0x730 mm/shmem.c:2565
 call_read_iter include/linux/fs.h:1895 [inline]
 do_iter_readv_writev+0x570/0x5d0 fs/read_write.c:691
 do_iter_read+0x1e4/0x3a0 fs/read_write.c:933
 vfs_iter_read+0x56/0x80 fs/read_write.c:975
 lo_read_simple drivers/block/loop.c:351 [inline]
 do_req_filebacked drivers/block/loop.c:625 [inline]
 loop_handle_cmd drivers/block/loop.c:1952 [inline]
 loop_queue_work+0x8d3/0x1514 drivers/block/loop.c:1966
 kthread_worker_fn+0x1d0/0x3c0 kernel/kthread.c:671
 loop_kthread_worker_fn+0x49/0x60 drivers/block/loop.c:901
 kthread+0x1cb/0x1f0 kernel/kthread.c:255
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffff88812c029b60 of 1 bytes by task 6492 on cpu 1:
 lru_add_drain_all+0x169/0x3a0 mm/swap.c:746
 invalidate_bdev+0x65/0x90 fs/block_dev.c:97
 btrfs_get_bdev_and_sb+0xb3/0x1a0 fs/btrfs/volumes.c:521
 btrfs_open_one_device fs/btrfs/volumes.c:624 [inline]
 open_fs_devices+0x3b2/0x610 fs/btrfs/volumes.c:1198
 btrfs_open_devices+0xb1/0xc0 fs/btrfs/volumes.c:1243
 btrfs_mount_root+0x4b8/0x9c0 fs/btrfs/super.c:1554
 legacy_get_tree+0x78/0xf0 fs/fs_context.c:622
 vfs_get_tree+0x52/0x190 fs/super.c:1547
 fc_mount+0x1d/0x80 fs/namespace.c:962
 vfs_kern_mount.part.0+0xe0/0xf0 fs/namespace.c:992
 vfs_kern_mount+0x46/0x60 fs/namespace.c:979
 btrfs_mount+0x250/0xf37 fs/btrfs/super.c:1642
 legacy_get_tree+0x78/0xf0 fs/fs_context.c:622
 vfs_get_tree+0x52/0x190 fs/super.c:1547
 do_new_mount fs/namespace.c:2822 [inline]
 do_mount+0xff0/0x14d0 fs/namespace.c:3107
 __do_sys_mount fs/namespace.c:3316 [inline]
 __se_sys_mount fs/namespace.c:3293 [inline]
 __x64_sys_mount+0x12b/0x1a0 fs/namespace.c:3293
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 6492 Comm: syz-executor.0 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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