a bit less contention with dirbench

37eec3b1 · Nickolai Zeldovich · 175e0c2e · 37eec3b1 · 37eec3b1
--- a/bio.c
+++ b/bio.c
@@ -145,9 +145,7 @@ bread(uint dev, uint sector, int writer)
  if(!(b->flags & B_VALID))
    iderw(b);
  if (writer && !origwriter) {
-    acquire(&b->lock);
-    b->flags &= ~B_BUSY;
-    release(&b->lock);
+    __sync_fetch_and_and(&b->flags, ~B_BUSY);
    cv_wakeup(&b->cv);
  }
  return b;
@@ -169,11 +167,9 @@ void
 brelse(struct buf *b, int writer)
 {
  if (writer) {
-    acquire(&b->lock);
    if((b->flags & B_BUSY) == 0)
      panic("brelse");
-    b->flags &= ~B_BUSY;
-    release(&b->lock);
+    __sync_fetch_and_and(&b->flags, ~B_BUSY);
    cv_wakeup(&b->cv);
  }
  // rcu_begin_read() happens in bread

--- a/fs.c
+++ b/fs.c
@@ -368,6 +368,8 @@ void
 iput(struct inode *ip)
 {
  if(__sync_sub_and_fetch(&ip->ref, 1) == 0) {
+    if (ip->nlink)
+      return;
    acquire(&ip->lock);
    if (ip->ref == 0 && ip->nlink == 0) {
      // inode is no longer used: truncate and free inode.