Some hacks to so that bmap callers don't need to hold the inode's lock

f57e3e36 · Silas Boyd-Wickizer · d0b095e0 · f57e3e36 · f57e3e36
--- a/include/file.hh
+++ b/include/file.hh
@@ -68,7 +68,7 @@ struct inode : public referenced, public rcu_freed
  short major;
  short minor;
  u32 size;
-  u32 addrs[NDIRECT+1];
+  std::atomic<u32> addrs[NDIRECT+1];

 private:
  inode();

--- a/kernel/fs.cc
+++ b/kernel/fs.cc
@@ -516,16 +516,28 @@ bmap(struct inode *ip, u32 bn)
  struct buf *bp;

  if(bn < NDIRECT){
-    if((addr = ip->addrs[bn]) == 0)
-      ip->addrs[bn] = addr = balloc(ip->dev);
+  retry0:
+    if((addr = ip->addrs[bn]) == 0) {
+      addr = balloc(ip->dev);
+      if (!cmpxch(&ip->addrs[bn], (u32)0, addr)) {
+        bfree(ip->dev, addr);
+        goto retry0;
+      }
+    }
    return addr;
  }
  bn -= NDIRECT;

  if(bn < NINDIRECT){
    // Load indirect block, allocating if necessary.
-    if((addr = ip->addrs[NDIRECT]) == 0)
-      ip->addrs[NDIRECT] = addr = balloc(ip->dev);
+  retry1:
+    if((addr = ip->addrs[NDIRECT]) == 0) {
+      addr = balloc(ip->dev);
+      if (!cmpxch(&ip->addrs[NDIRECT], (u32)0, addr)) {
+        bfree(ip->dev, addr);
+        goto retry1;
+      }
+    }

    int writerflag = 0;
    bp = bread(ip->dev, addr, writerflag);