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BUG: KCSAN: data-race in generic_file_buffered_read / truncate_setsize

write to 0xffff88821480c9d0 of 8 bytes by task 21795 on cpu 1:
 i_size_write include/linux/fs.h:897 [inline]
 truncate_setsize+0x2c/0xc0 mm/truncate.c:839
 fat_setattr+0x641/0x760 fs/fat/file.c:536
 notify_change+0x7d4/0xa20 fs/attr.c:336
 do_truncate+0xe0/0x120 fs/open.c:64
 handle_truncate fs/namei.c:2901 [inline]
 do_open fs/namei.c:3247 [inline]
 path_openat+0x1a4c/0x20e0 fs/namei.c:3360
 do_filp_open+0xbd/0x1d0 fs/namei.c:3387
 do_sys_openat2+0x33c/0x4a0 fs/open.c:1179
 do_sys_open fs/open.c:1195 [inline]
 ksys_open include/linux/syscalls.h:1388 [inline]
 __do_sys_creat fs/open.c:1263 [inline]
 __se_sys_creat fs/open.c:1261 [inline]
 __x64_sys_creat+0x62/0x80 fs/open.c:1261
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88821480c9d0 of 8 bytes by task 21791 on cpu 0:
 i_size_read include/linux/fs.h:875 [inline]
 generic_file_buffered_read+0xf9d/0x19e0 mm/filemap.c:2092
 generic_file_read_iter+0x7d/0x3e0 mm/filemap.c:2326
 call_read_iter include/linux/fs.h:1902 [inline]
 generic_file_splice_read+0x22a/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+0x562/0xb10 fs/read_write.c:1540
 __do_sys_sendfile64 fs/read_write.c:1595 [inline]
 __se_sys_sendfile64 fs/read_write.c:1587 [inline]
 __x64_sys_sendfile64+0xa9/0x130 fs/read_write.c:1587
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 21791 Comm: syz-executor.0 Not tainted 5.8.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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