Create a system call to add a process to prevent data race with the process list.

risc_v/src/syscall.rs

@@ -9,6 +9,8 @@ use crate::{block::block_op,
             page::{virt_to_phys, Table},
 			process::{delete_process, get_by_pid, set_sleeping, set_waiting}};
 			
+use crate::process::{PROCESS_LIST_MUTEX, PROCESS_LIST, Process};
+
 /// do_syscall is called from trap.rs to invoke a system call. No discernment is
 /// made here whether this is a U-mode, S-mode, or M-mode system call.
 /// Since we can't do anything unless we dereference the passed pointer,
@@ -41,6 +43,20 @@ pub unsafe fn do_syscall(mepc: usize, frame: *mut TrapFrame) -> usize {
 			set_sleeping((*frame).pid as u16, (*frame).regs[10]);
 			0
 		},
+		11 => {
+			// Add process to the scheduler. This is obviously insecure and
+			// we wouldn't do this realistically.
+			let my_proc = (*frame).regs[10] as *const Process;
+			PROCESS_LIST_MUTEX.spin_lock();
+			if let Some(mut pl) = PROCESS_LIST.take() {
+				// As soon as we push this process on the list, it'll be
+				// schedule-able.
+				pl.push_back(my_proc.read());
+				PROCESS_LIST.replace(pl);
+			}
+			PROCESS_LIST_MUTEX.unlock();
+			mepc + 4
+		},
 		63 => {
 			// Read system call
 			// This is an asynchronous call. This will get the
@@ -184,6 +200,10 @@ pub fn syscall_sleep(duration: usize)
 {
 	let _ = do_make_syscall(10, duration, 0, 0, 0, 0, 0);
 }
+
+pub fn syscall_add_process(process: Process) {
+	let _ = do_make_syscall(11, &process as *const Process as usize, 0, 0, 0, 0, 0);
+}
 // These system call numbers come from libgloss so that we can use newlib
 // for our system calls.
 // Libgloss wants the system call number in A7 and arguments in A0..A6

risc_v/src/test.rs

@@ -13,11 +13,9 @@ use crate::{cpu::{build_satp,
                       ProcessData,
                       ProcessState,
                       NEXT_PID,
-					  PROCESS_LIST,
-					  PROCESS_LIST_MUTEX,
                       STACK_ADDR,
                       STACK_PAGES},
-            syscall::syscall_fs_read};
+            syscall::{syscall_add_process, syscall_fs_read}};
 
 /// Test block will load raw binaries into memory to execute them. This function
 /// will load ELF files and try to execute them.
@@ -187,33 +185,13 @@ pub fn test_elf() {
 	// now. Since we don't reuse PIDs, this means that we can only spawn
 	// 65534 processes.
 	satp_fence_asid(my_pid as usize);
-	// I took a different tact here than in process.rs. In there I created
-	// the process while holding onto the process list. It might
-	// matter since this is asynchronous--it is being ran as a kernel process.
-	unsafe {
-		PROCESS_LIST_MUTEX.spin_lock();
-	}
-	if let Some(mut pl) = unsafe { PROCESS_LIST.take() } {
-		// As soon as we push this process on the list, it'll be
-		// schedule-able.
-		println!(
-		         "Added user process to the scheduler...get ready \
-		          for take-off!"
-		);
-		pl.push_back(my_proc);
-		unsafe {
-			PROCESS_LIST.replace(pl);
-		}
-	}
-	else {
-		println!("Unable to spawn process.");
-		// Since my_proc couldn't enter the process list, it
-		// will be dropped and all of the associated allocations
-		// will be deallocated through the process' Drop trait.
-	}
-	unsafe {
-		PROCESS_LIST_MUTEX.unlock();
-	}
+
+	// We will get a data race if we don't use the add process system call. This
+	// test process is being ran as a kernel process, which then competes with
+	// the scheduler due to the context switch timer. When we use a system call,
+	// it goes into an interrupt context so that the scheduler can safely
+	// receive our new process without preemption.
+	syscall_add_process(my_proc);
 	println!();
 }