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BUG: KCSAN: data-race in generic_file_buffered_read / simple_write_end

write to 0xffff88811d8d1d70 of 8 bytes by task 23697 on cpu 1:
 i_size_write include/linux/fs.h:876 [inline]
 simple_write_end+0x1fa/0x360 fs/libfs.c:587
 generic_perform_write+0x23b/0x390 mm/filemap.c:3512
 __generic_file_write_iter+0x154/0x330 mm/filemap.c:3630
 generic_file_write_iter+0x2f3/0x3e0 mm/filemap.c:3662
 call_write_iter include/linux/fs.h:1882 [inline]
 new_sync_write fs/read_write.c:503 [inline]
 vfs_write+0x665/0x6f0 fs/read_write.c:578
 ksys_write+0xce/0x180 fs/read_write.c:631
 __do_sys_write fs/read_write.c:643 [inline]
 __se_sys_write fs/read_write.c:640 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:640
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88811d8d1d70 of 8 bytes by task 23702 on cpu 0:
 i_size_read include/linux/fs.h:854 [inline]
 generic_file_buffered_read+0x126d/0x1f60 mm/filemap.c:2266
 generic_file_read_iter+0x7d/0x3e0 mm/filemap.c:2503
 call_read_iter include/linux/fs.h:1876 [inline]
 new_sync_read fs/read_write.c:415 [inline]
 vfs_read+0x57a/0x5e0 fs/read_write.c:481
 ksys_read+0xce/0x180 fs/read_write.c:607
 __do_sys_read fs/read_write.c:617 [inline]
 __se_sys_read fs/read_write.c:615 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:615
 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: 23702 Comm: syz-executor.1 Not tainted 5.9.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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