==================================================================
BUG: KCSAN: data-race in generic_file_buffered_read / generic_write_end

write to 0xffff88811347ccf8 of 8 bytes by task 27387 on cpu 1:
 i_size_write include/linux/fs.h:871 [inline]
 generic_write_end+0x99/0x240 fs/buffer.c:2186
 fat_write_end+0x4a/0x160 fs/fat/inode.c:249
 generic_perform_write+0x23b/0x390 mm/filemap.c:3516
 __generic_file_write_iter+0x22d/0x330 mm/filemap.c:3602
 generic_file_write_iter+0x2f0/0x3e0 mm/filemap.c:3666
 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:1299 [inline]
 __se_sys_sendfile64 fs/read_write.c:1285 [inline]
 __x64_sys_sendfile64+0xf2/0x130 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 0xffff88811347ccf8 of 8 bytes by task 27381 on cpu 0:
 i_size_read include/linux/fs.h:849 [inline]
 generic_file_buffered_read+0x12e2/0x1f50 mm/filemap.c:2266
 generic_file_read_iter+0x82/0x3e0 mm/filemap.c:2507
 call_read_iter include/linux/fs.h:1871 [inline]
 generic_file_splice_read+0x22a/0x310 fs/splice.c:311
 do_splice_to fs/splice.c:889 [inline]
 splice_direct_to_actor+0x2a8/0x660 fs/splice.c:969
 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:1299 [inline]
 __se_sys_sendfile64 fs/read_write.c:1285 [inline]
 __x64_sys_sendfile64+0xf2/0x130 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: 27381 Comm: syz-executor.3 Not tainted 5.9.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================