From e7a5b3c5ee2d440892ab7e9bb98ad82efb25219f Mon Sep 17 00:00:00 2001
From: rsc <rsc>
Date: Thu, 7 Sep 2006 16:53:49 +0000
Subject: [PATCH] comment memory barriers
---
spinlock.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/spinlock.c b/spinlock.c
index 486c217..2e604b7 100644
--- a/spinlock.c
+++ b/spinlock.c
@@ -50,6 +50,10 @@ acquire(struct spinlock *lock)
while(cmpxchg(0, 1, &lock->locked) == 1)
;
+
+ // Now that lock is acquired, make sure
+ // we wait for all pending writes from other
+ // processors.
cpuid(0, 0, 0, 0, 0); // memory barrier
// Record info about lock acquisition for debugging.
@@ -64,13 +68,16 @@ acquire(struct spinlock *lock)
void
release(struct spinlock *lock)
{
-
if(!holding(lock))
panic("release");
lock->pcs[0] = 0;
lock->cpu = 0xffffffff;
+
+ // Before unlocking the lock, make sure to flush
+ // any pending memory writes from this processor.
cpuid(0, 0, 0, 0, 0); // memory barrier
+
lock->locked = 0;
if(--cpus[cpu()].nlock == 0)
sti();
--
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