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BUG: KCSAN: data-race in __mark_inode_dirty / writeback_sb_inodes

write to 0xffff8881364e4c98 of 8 bytes by task 8200 on cpu 0:
 writeback_sb_inodes+0x4a1/0xff0 fs/fs-writeback.c:1712
 wb_writeback+0x27d/0x660 fs/fs-writeback.c:1896
 wb_do_writeback+0x101/0x5d0 fs/fs-writeback.c:2041
 wb_workfn+0xc8/0x430 fs/fs-writeback.c:2082
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2275
 worker_thread+0x616/0xa70 kernel/workqueue.c:2421
 kthread+0x20b/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffff8881364e4c98 of 8 bytes by task 15598 on cpu 1:
 __mark_inode_dirty+0xb4/0x6b0 fs/fs-writeback.c:2276
 generic_update_time fs/inode.c:1763 [inline]
 update_time fs/inode.c:1776 [inline]
 file_update_time+0x3ac/0x3f0 fs/inode.c:1991
 file_modified+0x62/0x80 fs/inode.c:2014
 ext4_write_checks fs/ext4/file.c:248 [inline]
 ext4_buffered_write_iter+0x1f9/0x3e0 fs/ext4/file.c:265
 ext4_file_write_iter+0x47a/0x1060 fs/ext4/file.c:503
 call_write_iter include/linux/fs.h:1901 [inline]
 do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:740
 do_iter_write+0x112/0x4c0 fs/read_write.c:866
 vfs_iter_write+0x4c/0x70 fs/read_write.c:907
 ovl_write_iter+0x629/0x8f0 fs/overlayfs/file.c:358
 call_write_iter include/linux/fs.h:1901 [inline]
 do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:740
 do_iter_write+0x112/0x4c0 fs/read_write.c:866
 vfs_iter_write+0x4c/0x70 fs/read_write.c:907
 iter_file_splice_write+0x41a/0x770 fs/splice.c:686
 do_splice_from fs/splice.c:764 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:933
 splice_direct_to_actor+0x345/0x650 fs/splice.c:888
 do_splice_direct+0xf5/0x170 fs/splice.c:976
 do_sendfile+0x5e0/0xcf0 fs/read_write.c:1257
 __do_sys_sendfile64 fs/read_write.c:1312 [inline]
 __se_sys_sendfile64 fs/read_write.c:1304 [inline]
 __x64_sys_sendfile64+0xa9/0x130 fs/read_write.c:1304
 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: 15598 Comm: syz-executor.2 Not tainted 5.11.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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