Bug in test-fork

[allanlw]

There is a non-deterministic bug in test-fork.

To reproduce, try: taskset -c 0 bash -c "rm userland/test-fork/output.txt; while true; do make test/test-fork || break; rm userland/test-fork/output.txt; done"

The failure will look something like:

allan@ubuntu-4gb-nyc3-01:~/silvos$ taskset -c 0 bash -c "rm userland/test-fork/output.txt; while true; do make test/test-fork || break; rm userland/test-fork/output.txt; done"
x86_64-elf-gcc -c userland/test-fork/main.c -o userland/test-fork/main.o -ffreestanding -Wall -Wextra -Wno-main -std=c99 -O2 -Iuserland
x86_64-elf-gcc userland/test-fork/main.o userland/startup.o -o userland/test-fork.bin -nostdlib -lgcc
dd if=/dev/zero of=userland/test-fork/test_disk bs=512 count=16
16+0 records in
16+0 records out
8192 bytes (8.2 kB, 8.0 KiB) copied, 0.000207988 s, 39.4 MB/s
qemu-system-x86_64 -kernel bootloader.multiboot \
        -d in_asm -D >( grep -E "^(Trace.*\[ffffffff|IN:|0xffffff)" | uniq > userland/test-fork/coverage.log) \
        -initrd george.multiboot,userland/test-fork.bin \
        -serial file:userland/test-fork/output.txt \
        -device isa-debug-exit,iobase=0xf4,iosize=0x04 \
        -nographic \
        -display none \
        -m 128 \
        -drive file=userland/test-fork/test_disk,index=0,media=disk,format=raw \
        | true
warning: TCG doesn't support requested feature: CPUID.01H:ECX.vmx [bit 5]
diff <(sort userland/test-fork/expected.txt) <(sort userland/test-fork/output.txt)
8,9c8,9
< THREAD 0x04: Child, depth 1
< THREAD 0x05: Child, depth 2
---
> THREAD 0x04: Child, depth 2
> THREAD 0x05: Child, depth 1
Makefile:117: recipe for target 'test/test-fork' failed
make: *** [test/test-fork] Error 1
rm userland/test-fork/test_disk userland/test-fork/main.o

This is pretty obviously some kind of race condition