BUG: KCSAN: data-race in sync_inodes_sb / xas_set_mark

write to 0xffff88811d4bb82c of 4 bytes by task 14985 on cpu 0:
 xa_mark_set lib/xarray.c:69 [inline]
 xas_set_mark lib/xarray.c:886 [inline]
 xas_set_mark+0x140/0x150 lib/xarray.c:870
 __xa_set_mark+0xdd/0x110 lib/xarray.c:1708
 __set_page_dirty+0x151/0x270 fs/buffer.c:618
 mark_buffer_dirty+0x26e/0x2b0 fs/buffer.c:1146
 __block_commit_write.isra.0+0x11d/0x170 fs/buffer.c:2075
 block_commit_write fs/buffer.c:2467 [inline]
 block_page_mkwrite+0x21d/0x230 fs/buffer.c:2516
 ext4_page_mkwrite+0x4e8/0x820 fs/ext4/inode.c:5958
 do_page_mkwrite+0xfa/0x210 mm/memory.c:2529
 wp_page_shared mm/memory.c:2856 [inline]
 do_wp_page+0xa07/0xca0 mm/memory.c:2973
 handle_pte_fault mm/memory.c:4231 [inline]
 __handle_mm_fault+0x2d96/0x2da0 mm/memory.c:4345
 handle_mm_fault+0x21c/0x540 mm/memory.c:4382
 do_user_addr_fault arch/x86/mm/fault.c:1464 [inline]
 do_page_fault+0x48a/0xa96 arch/x86/mm/fault.c:1535
 page_fault+0x34/0x40 arch/x86/entry/entry_64.S:1203

read to 0xffff88811d4bb82c of 4 bytes by task 9276 on cpu 1:
 mapping_tagged include/linux/fs.h:521 [inline]
 wait_sb_inodes fs/fs-writeback.c:2415 [inline]
 sync_inodes_sb+0x3c6/0x500 fs/fs-writeback.c:2558
 __sync_filesystem fs/sync.c:34 [inline]
 sync_filesystem fs/sync.c:67 [inline]
 sync_filesystem+0x12d/0x1a0 fs/sync.c:48
 ovl_sync_fs+0x89/0xa0 fs/overlayfs/super.c:277
 __sync_filesystem fs/sync.c:39 [inline]
 sync_filesystem fs/sync.c:67 [inline]
 sync_filesystem+0x15d/0x1a0 fs/sync.c:48
 generic_shutdown_super+0x68/0x270 fs/super.c:448
 kill_anon_super+0x28/0x50 fs/super.c:1108
 deactivate_locked_super+0x5d/0xb0 fs/super.c:335
 deactivate_super fs/super.c:366 [inline]
 deactivate_super+0xca/0xe0 fs/super.c:362
 cleanup_mnt+0x27a/0x330 fs/namespace.c:1102
 __cleanup_mnt+0x1c/0x30 fs/namespace.c:1109
 task_work_run+0xba/0x120 kernel/task_work.c:123
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x2ae/0x2c0 arch/x86/entry/common.c:165
 prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:279 [inline]
 do_syscall_64+0x38b/0x3b0 arch/x86/entry/common.c:305
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 9276 Comm: syz-executor.3 Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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