Merge #349

349: Fix WaitChannel's API r=efenniht a=travis1829

#241 작업을 하기 전에 먼저 `WaitChannel`의 지저분한 부분을 조금 다듬어봤습니다.
* 기존에는 `WaitChannel`에 대해서 sleep을 하기 위해서는 `SpinlockGuard`는 `sleep()`로, `SleepablelockGuard`는 `sleep_sleepable()`로, 그리고 `SpinlockProtected`는 `sleep_raw()`로 **여러가지로 API가 나눠져있는 걸 하나로 합쳤습니다.**
	* 이를 위해, `Guard`라는 trait을 추가했습니다. (현재 `SpinlockGuard`, `SpinlockProtectedGuard`, `SleepablelockGuard`이 이걸 impl합니다.)
* 다만, 별개로, **현재 `SleepablelockGuard::sleep()`이 `unsafe`이 아닌데, 이래도 괜찮은지 잘 모르겠습니다.** 	
	* 먼저, `WaitChannel::sleep()`이 `unsafe`한 이유는 `guard.sched()`을 call할때는 항상 `p->lock`이외에는 어떠한 RawSpinlock도 acquire한 상태여선 안되기 때문입니다. (`guard.sched()`내에서도 `assert_eq!((*kernel().mycpu()).noff, 1, "sched locks");`로 이걸 확인합니다). 그러나 `SleepablelockGuard::sleep()`은 내부에서 `WaitChannel::sleep()`을 사용하는데도 unsafe이 아닙니다.

Co-authored-by: travis1829 <[email protected]>

kernel-rs/src/proc.rs

@@ -19,11 +19,9 @@ use crate::{
     param::{MAXPROCNAME, NOFILE, NPROC, ROOTDEV},
     println,
     riscv::{intr_get, intr_on, r_tp, PGSIZE},
-    sleepablelock::SleepablelockGuard,
     some_or,
     spinlock::{
-        pop_off, push_off, RawSpinlock, Spinlock, SpinlockGuard, SpinlockProtected,
-        SpinlockProtectedGuard,
+        pop_off, push_off, RawSpinlock, Spinlock, SpinlockProtected, SpinlockProtectedGuard,
     },
     trap::usertrapret,
     vm::{PageTable, UVAddr, VAddr},
@@ -209,6 +207,26 @@ pub enum Procstate {
     USED,
 }
 
+/// Represents lock guards that can be slept in a `WaitChannel`.
+pub trait Waitable {
+    /// Releases the inner `RawSpinlock`.
+    ///
+    /// # Safety
+    ///
+    /// `raw_release()` and `raw_acquire` must always be used as a pair.
+    /// Use these only for temporarily releasing (and then acquiring) the lock.
+    /// Also, do not access `self` until re-acquiring the lock with `raw_acquire()`.
+    unsafe fn raw_release(&mut self);
+
+    /// Acquires the inner `RawSpinlock`.
+    ///
+    /// # Safety
+    ///
+    /// `raw_release()` and `raw_acquire` must always be used as a pair.
+    /// Use these only for temporarily releasing (and then acquiring) the lock.
+    unsafe fn raw_acquire(&mut self);
+}
+
 pub struct WaitChannel {
     /// Required to make this type non-zero-sized. If it were zero-sized, multiple wait channels may
     /// have the same address, spuriously waking up more threads.
@@ -222,23 +240,11 @@ impl WaitChannel {
 
     /// Atomically release lock and sleep on waitchannel.
     /// Reacquires lock when awakened.
-    pub unsafe fn sleep<T>(&self, guard: &mut SpinlockGuard<'_, T>) {
-        self.sleep_raw(guard.raw());
-    }
-
-    /// Atomically release lock and sleep on waitchannel.
-    /// Reacquires lock when awakened.
-    pub unsafe fn sleep_sleepable<T>(&self, guard: &mut SleepablelockGuard<'_, T>) {
-        self.sleep_raw(guard.raw());
-    }
-
-    /// Atomically release lock and sleep on waitchannel.
-    /// Reacquires lock when awakened.
-    // TODO(@kimjungwow): lk is not SpinlockGuard yet because
-    // 1. Some static mut variables are still not Spinlock<T> but RawSpinlock
-    // 2. Sleeplock doesn't have Spinlock<T>
-    pub unsafe fn sleep_raw(&self, lk: *const RawSpinlock) {
-        let p: *mut Proc = myproc();
+    pub fn sleep<T: Waitable>(&self, lk: &mut T) {
+        let p = unsafe {
+            // TODO: Remove this unsafe part after resolving #258
+            &*myproc()
+        };
 
         // Must acquire p->lock in order to
         // change p->state and then call sched.
@@ -248,22 +254,32 @@ impl WaitChannel {
         // so it's okay to release lk.
 
         //DOC: sleeplock1
-        mem::forget((*p).info.lock());
-        (*lk).release();
+        let mut guard = p.lock();
+        unsafe {
+            // Temporarily release the inner `RawSpinlock`.
+            // This is safe, since we don't access `lk` until re-acquiring the lock
+            // at `lk.raw_acquire()`.
+            lk.raw_release();
+        }
 
         // Go to sleep.
-        let mut guard = ProcGuard::from_raw(p);
         guard.deref_mut_info().waitchannel = self;
         guard.deref_mut_info().state = Procstate::SLEEPING;
-        guard.sched();
+        unsafe {
+            // Safe since we hold `p.lock()`, changed the process's state,
+            // and device interrupts are disabled by `push_off()` in `p.lock()`.
+            guard.sched();
+        }
 
         // Tidy up.
         guard.deref_mut_info().waitchannel = ptr::null();
-        mem::forget(guard);
 
         // Reacquire original lock.
-        (*p).info.unlock();
-        (*lk).acquire();
+        drop(guard);
+        unsafe {
+            // Safe since this is paired with a previous `lk.raw_release()`.
+            lk.raw_acquire();
+        }
     }
 
     /// Wake up all processes sleeping on waitchannel.
@@ -801,7 +817,7 @@ impl ProcessSystem {
 
             // Wait for a child to exit.
             //DOC: wait-sleep
-            ((*p).info.get_mut_unchecked().child_waitchannel).sleep_raw(parent_guard.raw());
+            ((*p).info.get_mut_unchecked().child_waitchannel).sleep(&mut parent_guard);
         }
     }
 

kernel-rs/src/sleepablelock.rs

@@ -1,5 +1,5 @@
 //! Sleepable locks
-use crate::proc::WaitChannel;
+use crate::proc::{WaitChannel, Waitable};
 use crate::spinlock::RawSpinlock;
 use core::cell::UnsafeCell;
 use core::marker::PhantomData;
@@ -60,23 +60,24 @@ impl<T> Sleepablelock<T> {
 }
 
 impl<T> SleepablelockGuard<'_, T> {
-    pub fn raw(&self) -> *const RawSpinlock {
-        &self.lock.lock as *const _
-    }
-
     pub fn sleep(&mut self) {
-        unsafe {
-            self.lock
-                .waitchannel
-                .sleep_raw(&self.lock.lock as *const _ as *mut RawSpinlock);
-        }
+        self.lock.waitchannel.sleep(self);
     }
 
     pub fn wakeup(&self) {
         self.lock.waitchannel.wakeup();
     }
 }
 
+impl<T> Waitable for SleepablelockGuard<'_, T> {
+    unsafe fn raw_release(&mut self) {
+        self.lock.lock.release();
+    }
+    unsafe fn raw_acquire(&mut self) {
+        self.lock.lock.acquire();
+    }
+}
+
 impl<T> Drop for SleepablelockGuard<'_, T> {
     fn drop(&mut self) {
         self.lock.lock.release();

kernel-rs/src/spinlock.rs

@@ -1,6 +1,6 @@
 use crate::{
     kernel::kernel,
-    proc::Cpu,
+    proc::{Cpu, Waitable},
     riscv::{intr_get, intr_off, intr_on},
 };
 use core::cell::UnsafeCell;
@@ -187,10 +187,6 @@ impl<T> Spinlock<T> {
 }
 
 impl<T> SpinlockGuard<'_, T> {
-    pub fn raw(&self) -> *const RawSpinlock {
-        &self.lock.lock as *const _
-    }
-
     pub fn reacquire_after<F, R>(&mut self, f: F) -> R
     where
         F: FnOnce() -> R,
@@ -202,6 +198,15 @@ impl<T> SpinlockGuard<'_, T> {
     }
 }
 
+impl<T> Waitable for SpinlockGuard<'_, T> {
+    unsafe fn raw_release(&mut self) {
+        self.lock.lock.release();
+    }
+    unsafe fn raw_acquire(&mut self) {
+        self.lock.lock.acquire();
+    }
+}
+
 impl<T> Drop for SpinlockGuard<'_, T> {
     fn drop(&mut self) {
         self.lock.lock.release();
@@ -262,10 +267,12 @@ impl<T> SpinlockProtected<T> {
     }
 }
 
-impl SpinlockProtectedGuard<'_> {
-    /// Returns the inner `RawSpinlock`.
-    pub fn raw(&self) -> *const RawSpinlock {
-        self.lock as *const _
+impl Waitable for SpinlockProtectedGuard<'_> {
+    unsafe fn raw_release(&mut self) {
+        self.lock.release();
+    }
+    unsafe fn raw_acquire(&mut self) {
+        self.lock.acquire();
     }
 }
 

kernel-rs/src/virtio_disk.rs

@@ -317,7 +317,7 @@ impl Disk {
 
         // Wait for virtio_disk_intr() to say request has finished.
         while b.deref_mut_inner().disk {
-            (*b).vdisk_request_waitchannel.sleep_sleepable(this);
+            (*b).vdisk_request_waitchannel.sleep(this);
         }
         this.info[desc[0].idx].b = ptr::null_mut();
         IntoIter::new(desc).for_each(|desc| this.desc.free(desc));