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BUG: KCSAN: data-race in generic_file_buffered_read / generic_write_end

write to 0xffff88810e3866b0 of 8 bytes by task 16001 on cpu 1:
 i_size_write include/linux/fs.h:871 [inline]
 generic_write_end+0x98/0x250 fs/buffer.c:2186
 ext4_da_write_end+0x59b/0x760 fs/ext4/inode.c:3102
 generic_perform_write+0x23e/0x3a0 mm/filemap.c:3340
 ext4_buffered_write_iter+0x2e5/0x3d0 fs/ext4/file.c:270
 ext4_file_write_iter+0x45e/0x1090 fs/ext4/file.c:503
 call_write_iter include/linux/fs.h:1903 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x6d4/0x7c0 fs/read_write.c:605
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88810e3866b0 of 8 bytes by task 16005 on cpu 0:
 i_size_read include/linux/fs.h:849 [inline]
 generic_file_buffered_read+0x1426/0x23a0 mm/filemap.c:2302
 generic_file_read_iter+0x80/0x3d0 mm/filemap.c:2553
 ext4_file_read_iter+0x2d0/0x420 fs/ext4/file.c:74
 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: 0 PID: 16005 Comm: syz-executor.1 Not tainted 5.10.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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