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BUG: KCSAN: data-race in sync_inodes_sb / xas_set_mark

write to 0xffff8880b645f464 of 4 bytes by task 11682 on cpu 0:
 xa_mark_set lib/xarray.c:68 [inline]
 xas_set_mark lib/xarray.c:885 [inline]
 xas_set_mark+0x14d/0x160 lib/xarray.c:869
 __xa_set_mark+0xd3/0x100 lib/xarray.c:1699
 __set_page_dirty+0x152/0x270 fs/buffer.c:584
 mark_buffer_dirty+0x27f/0x2c0 fs/buffer.c:1112
 __block_commit_write.isra.0+0x11f/0x170 fs/buffer.c:2041
 block_commit_write fs/buffer.c:2433 [inline]
 block_page_mkwrite+0x226/0x230 fs/buffer.c:2482
 ext4_page_mkwrite+0x5af/0xce0 fs/ext4/inode.c:6217
 do_page_mkwrite+0x100/0x210 mm/memory.c:2208
 wp_page_shared mm/memory.c:2507 [inline]
 do_wp_page+0xd65/0x11f0 mm/memory.c:2619
 handle_pte_fault mm/memory.c:3865 [inline]
 __handle_mm_fault+0x1ab1/0x2c70 mm/memory.c:3973
 handle_mm_fault+0x21b/0x530 mm/memory.c:4010
 do_user_addr_fault arch/x86/mm/fault.c:1441 [inline]
 __do_page_fault+0x456/0x8d0 arch/x86/mm/fault.c:1506
 do_page_fault+0x38/0x194 arch/x86/mm/fault.c:1530
 page_fault+0x34/0x40 arch/x86/entry/entry_64.S:1202

read to 0xffff8880b645f464 of 4 bytes by task 10397 on cpu 1:
 mapping_tagged include/linux/fs.h:521 [inline]
 wait_sb_inodes fs/fs-writeback.c:2415 [inline]
 sync_inodes_sb+0x2c7/0x410 fs/fs-writeback.c:2558
 __sync_filesystem fs/sync.c:34 [inline]
 sync_filesystem fs/sync.c:67 [inline]
 sync_filesystem+0x138/0x1a0 fs/sync.c:48
 ovl_sync_fs+0x92/0xa0 fs/overlayfs/super.c:276
 __sync_filesystem fs/sync.c:39 [inline]
 sync_filesystem fs/sync.c:67 [inline]
 sync_filesystem+0x168/0x1a0 fs/sync.c:48
 generic_shutdown_super+0x6b/0x260 fs/super.c:448
 kill_anon_super+0x2f/0x50 fs/super.c:1106
 deactivate_locked_super+0x64/0xb0 fs/super.c:335
 deactivate_super fs/super.c:366 [inline]
 deactivate_super+0xca/0xe0 fs/super.c:362
 cleanup_mnt+0x27f/0x330 fs/namespace.c:1102
 __cleanup_mnt+0x1f/0x30 fs/namespace.c:1109
 task_work_run+0xf6/0x130 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x2b4/0x2c0 arch/x86/entry/common.c:163
 prepare_exit_to_usermode arch/x86/entry/common.c:194 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:274 [inline]
 do_syscall_64+0x353/0x370 arch/x86/entry/common.c:300
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 10397 Comm: syz-executor.3 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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