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BUG: KCSAN: data-race in __filemap_fdatawrite_range / __xa_set_mark

write to 0xffff88812b8705fc of 4 bytes by task 7611 on cpu 1:
 xa_mark_set lib/xarray.c:69 [inline]
 xas_set_mark lib/xarray.c:886 [inline]
 __xa_set_mark+0x2e9/0x300 lib/xarray.c:1708
 __set_page_dirty+0x17e/0x1d0 fs/buffer.c:609
 mark_buffer_dirty+0x126/0x230 fs/buffer.c:1137
 __ext4_handle_dirty_metadata+0x20a/0x5a0 fs/ext4/ext4_jbd2.c:362
 ext4_do_update_inode fs/ext4/inode.c:5072 [inline]
 ext4_mark_iloc_dirty+0x1302/0x1660 fs/ext4/inode.c:5624
 __ext4_mark_inode_dirty+0x44c/0x600 fs/ext4/inode.c:5818
 ext4_dirty_inode+0xa6/0xc0 fs/ext4/inode.c:5854
 __mark_inode_dirty+0x72/0x740 fs/fs-writeback.c:2260
 generic_update_time fs/inode.c:1762 [inline]
 update_time fs/inode.c:1775 [inline]
 file_update_time+0x3a8/0x3f0 fs/inode.c:1990
 ext4_page_mkwrite+0xe3/0xae0 fs/ext4/inode.c:5972
 do_page_mkwrite mm/memory.c:2702 [inline]
 wp_page_shared+0x2d8/0x810 mm/memory.c:3031
 do_wp_page+0x6eb/0x740 mm/memory.c:3124
 handle_pte_fault mm/memory.c:4390 [inline]
 __handle_mm_fault mm/memory.c:4507 [inline]
 handle_mm_fault+0x1899/0x1af0 mm/memory.c:4605
 do_user_addr_fault+0x380/0x770 arch/x86/mm/fault.c:1372
 handle_page_fault arch/x86/mm/fault.c:1429 [inline]
 exc_page_fault+0xb8/0x310 arch/x86/mm/fault.c:1482
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:583

read to 0xffff88812b8705fc of 4 bytes by task 8706 on cpu 0:
 xa_marked include/linux/xarray.h:416 [inline]
 mapping_tagged include/linux/fs.h:488 [inline]
 __filemap_fdatawrite_range+0x11c/0x1d0 mm/filemap.c:418
 __filemap_fdatawrite mm/filemap.c:430 [inline]
 filemap_flush+0x1f/0x30 mm/filemap.c:457
 __sync_blockdev+0x69/0x70 fs/block_dev.c:508
 __sync_filesystem fs/sync.c:40 [inline]
 sync_filesystem+0xcb/0x160 fs/sync.c:64
 ovl_sync_fs+0x74/0x90 fs/overlayfs/super.c:281
 __sync_filesystem fs/sync.c:39 [inline]
 sync_filesystem+0x112/0x160 fs/sync.c:67
 generic_shutdown_super+0x42/0x210 fs/super.c:448
 kill_anon_super+0x23/0x40 fs/super.c:1108
 deactivate_locked_super+0x6a/0xb0 fs/super.c:335
 deactivate_super+0x85/0x90 fs/super.c:366
 cleanup_mnt+0x277/0x2e0 fs/namespace.c:1118
 __cleanup_mnt+0x15/0x20 fs/namespace.c:1125
 task_work_run+0x8e/0x110 kernel/task_work.c:141
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:165 [inline]
 exit_to_user_mode_prepare+0x1b2/0x210 kernel/entry/common.c:192
 syscall_exit_to_user_mode+0x16/0x30 kernel/entry/common.c:267
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8706 Comm: syz-executor.1 Not tainted 5.9.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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