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BUG: KCSAN: data-race in __writeback_single_inode / ext4_sync_file

write to 0xffff88812a3f6688 of 8 bytes by task 24662 on cpu 1:
 __writeback_single_inode+0x256/0x580 fs/fs-writeback.c:1492
 writeback_single_inode+0x11f/0x580 fs/fs-writeback.c:1570
 sync_inode fs/fs-writeback.c:2606 [inline]
 sync_inode_metadata+0x52/0x70 fs/fs-writeback.c:2626
 ext4_fsync_nojournal fs/ext4/fsync.c:92 [inline]
 ext4_sync_file+0x335/0x690 fs/ext4/fsync.c:170
 vfs_fsync_range+0x107/0x120 fs/sync.c:200
 generic_write_sync include/linux/fs.h:2741 [inline]
 ext4_buffered_write_iter+0x36b/0x3b0 fs/ext4/file.c:276
 ext4_file_write_iter+0x49e/0x1060 include/linux/fs.h:779
 call_write_iter include/linux/fs.h:1877 [inline]
 do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:721
 do_iter_write+0x112/0x4b0 fs/read_write.c:847
 vfs_iter_write+0x4c/0x70 fs/read_write.c:888
 iter_file_splice_write+0x41a/0x770 fs/splice.c:769
 do_splice_from fs/splice.c:865 [inline]
 direct_splice_actor+0x95/0x160 fs/splice.c:1035
 splice_direct_to_actor+0x365/0x660 fs/splice.c:990
 do_splice_direct+0xf2/0x170 fs/splice.c:1078
 do_sendfile+0x56a/0xba0 fs/read_write.c:1238
 __do_sys_sendfile64 fs/read_write.c:1293 [inline]
 __se_sys_sendfile64 fs/read_write.c:1285 [inline]
 __x64_sys_sendfile64+0xa9/0x130 fs/read_write.c:1285
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812a3f6688 of 8 bytes by task 24669 on cpu 0:
 ext4_fsync_nojournal fs/ext4/fsync.c:87 [inline]
 ext4_sync_file+0x26c/0x690 fs/ext4/fsync.c:170
 vfs_fsync_range+0x107/0x120 fs/sync.c:200
 generic_write_sync include/linux/fs.h:2741 [inline]
 ext4_buffered_write_iter+0x36b/0x3b0 fs/ext4/file.c:276
 ext4_file_write_iter+0x49e/0x1060 include/linux/fs.h:779
 call_write_iter include/linux/fs.h:1877 [inline]
 do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:721
 do_iter_write+0x112/0x4b0 fs/read_write.c:847
 vfs_iter_write+0x4c/0x70 fs/read_write.c:888
 iter_file_splice_write+0x41a/0x770 fs/splice.c:769
 do_splice_from fs/splice.c:865 [inline]
 direct_splice_actor+0x95/0x160 fs/splice.c:1035
 splice_direct_to_actor+0x365/0x660 fs/splice.c:990
 do_splice_direct+0xf2/0x170 fs/splice.c:1078
 do_sendfile+0x56a/0xba0 fs/read_write.c:1238
 __do_sys_sendfile64 fs/read_write.c:1293 [inline]
 __se_sys_sendfile64 fs/read_write.c:1285 [inline]
 __x64_sys_sendfile64+0xa9/0x130 fs/read_write.c:1285
 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: 0 PID: 24669 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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