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BUG: KCSAN: data-race in activate_page / lru_add_drain_all

read to 0xffff88812c129760 of 1 bytes by task 14758 on cpu 0:
 need_activate_page_drain mm/swap.c:304 [inline]
 lru_add_drain_all+0x3a2/0x3d0 mm/swap.c:751
 invalidate_bdev+0x6e/0x90 fs/block_dev.c:97
 btrfs_get_bdev_and_sb+0xbb/0x1a0 fs/btrfs/volumes.c:510
 btrfs_open_one_device fs/btrfs/volumes.c:613 [inline]
 open_fs_devices+0x3ae/0x610 fs/btrfs/volumes.c:1156
 btrfs_open_devices+0xc5/0xd0 fs/btrfs/volumes.c:1201
 btrfs_mount_root+0x4b8/0x9c0 fs/btrfs/super.c:1533
 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:2822 [inline]
 do_mount+0x1004/0x14f0 fs/namespace.c:3142
 ksys_mount+0xe8/0x160 fs/namespace.c:3351
 __do_sys_mount fs/namespace.c:3365 [inline]
 __se_sys_mount fs/namespace.c:3362 [inline]
 __x64_sys_mount+0x70/0x90 fs/namespace.c:3362
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff88812c129760 of 1 bytes by task 14773 on cpu 1:
 pagevec_add include/linux/pagevec.h:81 [inline]
 activate_page+0x24f/0x380 mm/swap.c:314
 mark_page_accessed+0x2ba/0x520 mm/swap.c:393
 shmem_file_read_iter+0x59c/0x720 mm/shmem.c:2605
 call_read_iter include/linux/fs.h:1896 [inline]
 do_iter_readv_writev+0x54b/0x5b0 fs/read_write.c:691
 do_iter_read+0x1fc/0x3d0 fs/read_write.c:933
 vfs_iter_read+0x5c/0x80 fs/read_write.c:947
 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+0x92c/0x1623 drivers/block/loop.c:1966
 kthread_worker_fn+0x1c3/0x3a0 kernel/kthread.c:671
 loop_kthread_worker_fn+0x50/0x70 drivers/block/loop.c:901
 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: 14773 Comm: loop3 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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