Merge branch 'riscv' of g.csail.mit.edu:xv6-dev into riscv

1 files changed, 6 insertions, 7 deletions

diff --git a/kernel/spinlock.c b/kernel/spinlock.c
index 5a44a46..83512bb 100644
--- a/kernel/spinlock.c
+++ b/kernel/spinlock.c
@@ -18,8 +18,6 @@ initlock(struct spinlock *lk, char *name)
 
 // Acquire the lock.
 // Loops (spins) until the lock is acquired.
-// Holding a lock for a long time may cause
-// other CPUs to waste time spinning to acquire it.
 void
 acquire(struct spinlock *lk)
 {
@@ -27,7 +25,7 @@ acquire(struct spinlock *lk)
   if(holding(lk))
     panic("acquire");
 
-  // On RISC-V, this turns into an atomic swap:
+  // On RISC-V, sync_lock_test_and_set turns into an atomic swap:
   //   a5 = 1
   //   s1 = &lk->locked
   //   amoswap.w.aq a5, a5, (s1)
@@ -59,9 +57,10 @@ release(struct spinlock *lk)
   __sync_synchronize();
 
   // Release the lock, equivalent to lk->locked = 0.
-  // This code can't use a C assignment, since it might
-  // not be atomic.
-  // On RISC-V, this turns into an atomic swap:
+  // This code doesn't use a C assignment, since the C standard
+  // implies that an assignment might be implemented with
+  // multiple store instructions.
+  // On RISC-V, sync_lock_release turns into an atomic swap:
   //   s1 = &lk->locked
   //   amoswap.w zero, zero, (s1)
   __sync_lock_release(&lk->locked);
@@ -81,7 +80,7 @@ holding(struct spinlock *lk)
 }
 
 // push_off/pop_off are like intr_off()/intr_on() except that they are matched:
-// it takes two pop_off to undo two push_off.  Also, if interrupts
+// it takes two pop_off()s to undo two push_off()s.  Also, if interrupts
 // are initially off, then push_off, pop_off leaves them off.
 
 void