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BUG: KCSAN: data-race in __writeback_single_inode / ext4_set_iomap

read-write to 0xffff88810e786c58 of 8 bytes by task 20960 on cpu 0:
 __writeback_single_inode+0x248/0x560 fs/fs-writeback.c:1492
 writeback_single_inode+0x126/0x580 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+0x359/0x6c0 fs/ext4/fsync.c:170
 vfs_fsync_range+0x107/0x120 fs/sync.c:200
 generic_write_sync include/linux/fs.h:2739 [inline]
 ext4_buffered_write_iter+0x384/0x3d0 fs/ext4/file.c:278
 ext4_file_write_iter+0x45e/0x1090 fs/ext4/file.c:503
 call_write_iter include/linux/fs.h:1903 [inline]
 do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:740
 do_iter_write+0x112/0x4b0 fs/read_write.c:866
 vfs_iter_write+0x4c/0x70 fs/read_write.c:907
 iter_file_splice_write+0x42a/0x780 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+0x5db/0xca0 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

read to 0xffff88810e786c58 of 8 bytes by task 20957 on cpu 1:
 ext4_inode_datasync_dirty fs/ext4/inode.c:3322 [inline]
 ext4_set_iomap+0x182/0x440 fs/ext4/inode.c:3337
 ext4_iomap_begin+0x641/0x690 fs/ext4/inode.c:3476
 iomap_apply+0x8d/0x4a0 fs/iomap/apply.c:46
 __iomap_dio_rw+0x448/0x9b0 fs/iomap/direct-io.c:517
 iomap_dio_rw+0x30/0x70 fs/iomap/direct-io.c:605
 ext4_dio_read_iter fs/ext4/file.c:77 [inline]
 ext4_file_read_iter+0x3bd/0x420 fs/ext4/file.c:129
 call_read_iter include/linux/fs.h:1897 [inline]
 generic_file_splice_read+0x22a/0x310 fs/splice.c:311
 do_splice_to fs/splice.c:788 [inline]
 splice_direct_to_actor+0x2aa/0x650 fs/splice.c:867
 do_splice_direct+0xf5/0x170 fs/splice.c:976
 do_sendfile+0x5db/0xca0 fs/read_write.c:1257
 __do_sys_sendfile64 fs/read_write.c:1318 [inline]
 __se_sys_sendfile64 fs/read_write.c:1304 [inline]
 __x64_sys_sendfile64+0xf2/0x130 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: 20957 Comm: syz-executor.1 Not tainted 5.10.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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