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BUG: KCSAN: data-race in ext4_handle_inode_extension / ondemand_readahead

write to 0xffff8880a61e4bc8 of 8 bytes by task 10907 on cpu 1:
 i_size_write include/linux/fs.h:876 [inline]
 ext4_update_inode_size fs/ext4/ext4.h:3141 [inline]
 ext4_handle_inode_extension+0x214/0x530 fs/ext4/file.c:330
 ext4_dio_write_iter fs/ext4/file.c:554 [inline]
 ext4_file_write_iter+0xe17/0x1060 fs/ext4/file.c:658
 call_write_iter include/linux/fs.h:1882 [inline]
 do_iter_readv_writev+0x32e/0x3d0 fs/read_write.c:721
 do_iter_write+0x112/0x4b0 fs/read_write.c:1026
 vfs_iter_write+0x4c/0x70 fs/read_write.c:1067
 iter_file_splice_write+0x41a/0x770 fs/splice.c:750
 do_splice_from fs/splice.c:846 [inline]
 direct_splice_actor+0x95/0x160 fs/splice.c:1016
 splice_direct_to_actor+0x365/0x660 fs/splice.c:971
 do_splice_direct+0xf2/0x170 fs/splice.c:1059
 do_sendfile+0x56a/0xba0 fs/read_write.c:1548
 __do_sys_sendfile64 fs/read_write.c:1609 [inline]
 __se_sys_sendfile64 fs/read_write.c:1595 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1595
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880a61e4bc8 of 8 bytes by task 10910 on cpu 0:
 i_size_read include/linux/fs.h:854 [inline]
 __do_page_cache_readahead mm/readahead.c:260 [inline]
 ra_submit mm/internal.h:64 [inline]
 ondemand_readahead+0x475/0x6e0 mm/readahead.c:551
 page_cache_sync_readahead+0x178/0x1a0 mm/readahead.c:585
 generic_file_buffered_read+0x2ec/0x1f60 mm/filemap.c:2199
 generic_file_read_iter+0x7d/0x3e0 mm/filemap.c:2503
 ext4_file_read_iter+0x2d8/0x420 fs/ext4/file.c:74
 call_read_iter include/linux/fs.h:1876 [inline]
 generic_file_splice_read+0x22b/0x310 fs/splice.c:312
 do_splice_to fs/splice.c:870 [inline]
 splice_direct_to_actor+0x2a8/0x660 fs/splice.c:950
 do_splice_direct+0xf2/0x170 fs/splice.c:1059
 do_sendfile+0x56a/0xba0 fs/read_write.c:1548
 __do_sys_sendfile64 fs/read_write.c:1603 [inline]
 __se_sys_sendfile64 fs/read_write.c:1595 [inline]
 __x64_sys_sendfile64+0xa9/0x130 fs/read_write.c:1595
 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: 10910 Comm: syz-executor.0 Not tainted 5.9.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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