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BUG: KCSAN: data-race in activate_page / lru_add_drain_all

write to 0xffff88812c028cc0 of 1 bytes by task 28201 on cpu 0:
 pagevec_add include/linux/pagevec.h:81 [inline]
 activate_page+0x1a4/0x2d0 mm/swap.c:360
 mark_page_accessed+0x20e/0x340 mm/swap.c:442
 shmem_getpage_gfp+0x353/0x19c0 mm/shmem.c:1828
 shmem_getpage mm/shmem.c:155 [inline]
 shmem_write_begin+0x83/0x100 mm/shmem.c:2523
 generic_perform_write+0x196/0x390 mm/filemap.c:3505
 __generic_file_write_iter+0x154/0x330 mm/filemap.c:3634
 generic_file_write_iter+0x2f3/0x3e0 mm/filemap.c:3666
 call_write_iter include/linux/fs.h:1882 [inline]
 do_iter_readv_writev+0x32e/0x3d0 fs/read_write.c:721
 do_iter_write+0x112/0x4b0 fs/read_write.c:1026
 vfs_iter_write+0x4c/0x70 fs/read_write.c:1067
 lo_write_bvec+0xc4/0x1e0 drivers/block/loop.c:287
 lo_write_simple drivers/block/loop.c:309 [inline]
 do_req_filebacked drivers/block/loop.c:632 [inline]
 loop_handle_cmd drivers/block/loop.c:2048 [inline]
 loop_queue_work+0x11f6/0x14c0 drivers/block/loop.c:2066
 kthread_worker_fn+0x283/0x3b0 kernel/kthread.c:708
 loop_kthread_worker_fn+0x3e/0x50 drivers/block/loop.c:937
 kthread+0x20d/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff88812c028cc0 of 1 bytes by task 28199 on cpu 1:
 pagevec_count include/linux/pagevec.h:68 [inline]
 need_activate_page_drain mm/swap.c:348 [inline]
 lru_add_drain_all+0x20b/0x3b0 mm/swap.c:801
 invalidate_bdev+0x50/0x70 fs/block_dev.c:96
 open_ctree+0x627/0x259c fs/btrfs/disk-io.c:2919
 btrfs_fill_super fs/btrfs/super.c:1316 [inline]
 btrfs_mount_root+0x742/0x830 fs/btrfs/super.c:1672
 legacy_get_tree+0x70/0xc0 fs/fs_context.c:592
 vfs_get_tree+0x4d/0x1a0 fs/super.c:1547
 fc_mount fs/namespace.c:978 [inline]
 vfs_kern_mount+0xc6/0x130 fs/namespace.c:1008
 btrfs_mount+0x27b/0x790 fs/btrfs/super.c:1732
 legacy_get_tree+0x70/0xc0 fs/fs_context.c:592
 vfs_get_tree+0x4d/0x1a0 fs/super.c:1547
 do_new_mount fs/namespace.c:2875 [inline]
 path_mount+0x118d/0x1c70 fs/namespace.c:3192
 do_mount fs/namespace.c:3205 [inline]
 __do_sys_mount fs/namespace.c:3413 [inline]
 __se_sys_mount+0x126/0x180 fs/namespace.c:3390
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3390
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 28199 Comm: syz-executor.5 Not tainted 5.9.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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