vmap::tryinc tries to get a reference on a rcu_freed vmap

8bea9485 · Silas Boyd-Wickizer · 30028bd5 · 8bea9485 · 8bea9485 · 8bea9485
--- a/include/uwq.hh
+++ b/include/uwq.hh
@@ -7,7 +7,7 @@ struct padded_length {

 #if defined (XV6_KERNEL)
 struct uwq {
-  uwq(padded_length *len);
+  uwq(vmap* vmap, padded_length *len);
  ~uwq();
  bool  haswork();
  int   trywork();
@@ -19,6 +19,7 @@ private:
  proc* getworker();

  struct spinlock lock_;
+  vmap* vmap_;
  padded_length* len_;

  struct worker {

--- a/include/vm.hh
+++ b/include/vm.hh
@@ -81,6 +81,8 @@ struct vmap : public rcu_freed {
  bool replace_vma(vma *a, vma *b);

  void decref();
+  bool tryinc();
+
  vmap* copy(int share);
  vma* lookup(uptr start, uptr len);
  int insert(vmnode *n, uptr va_start, int dotlb);

--- a/kernel/uwq.cc
+++ b/kernel/uwq.cc
@@ -25,7 +25,7 @@ uwq_trywork(void)
      continue;
    struct cpu *c = &cpus[j];

-    scoped_gc_epoch gcx();
+    scoped_gc_epoch xgc();
    barrier();
    struct proc *p = c->proc;
    if (p == nullptr || p->vmap == nullptr)
@@ -45,8 +45,8 @@ uwq_trywork(void)
 //
 // uwq
 //
-uwq::uwq(padded_length *len) 
-  : len_(len)
+uwq::uwq(vmap* vmap, padded_length *len) 
+  : vmap_(vmap), len_(len)
 {
  if (len_ != nullptr) {
    for (int i = 0; i < NCPU; i++)
@@ -63,6 +63,7 @@ uwq::~uwq(void)
 { 
  if (len_ != nullptr)
    ksfree(slab_userwq, len_);
+  // XXX(sbw) clean up worker procs
 }

 bool
@@ -88,6 +89,12 @@ uwq::trywork(void)
  if (p == nullptr)
    return -1;

+  if (!vmap_->tryinc())
+    return -1;
+
+  // XXX(sbw)
+  vmap_->decref();
+  panic("XXX");
  return 0;
 }

@@ -114,8 +121,12 @@ uwq::getworker(void)
  }

  if (slot != -1) {
-    
-    panic("XXX");
+    proc* p = allocproc();
+    if (p != nullptr) {
+      worker_[slot].proc = p;
+      worker_[slot].running = 1;
+      return worker_[slot].proc;
+    }
  }

  return nullptr;

--- a/kernel/vm.cc
+++ b/kernel/vm.cc
@@ -145,7 +145,8 @@ vmap::alloc(void)
  return new vmap();
 }

-vmap::vmap() : rcu_freed("vm"),
+vmap::vmap() : 
+  rcu_freed("vm"),
 #if VM_CRANGE
  cr(10),
 #endif
@@ -153,7 +154,7 @@ vmap::vmap() : rcu_freed("vm"),
  rx(PGSHIFT),
 #endif
  ref(1), pml4(setupkvm()), kshared((char*) ksalloc(slab_kshared)),
-  brk_(0), uwq_((padded_length*) ksalloc(slab_userwq))
+  brk_(0), uwq_(this, (padded_length*) ksalloc(slab_userwq))
 {
  initlock(&brklock_, "brk_lock", LOCKSTAT_VM);
  if (pml4 == 0) {
@@ -202,6 +203,20 @@ vmap::decref()
 }

 bool
+vmap::tryinc()
+{
+  u64 o;
+
+  do {
+    o = ref.load();
+    if (o == 0)
+      return false;
+  } while (!cmpxch(&ref, o, o+1));
+
+  return true;
+}
+
+bool
 vmap::replace_vma(vma *a, vma *b)
 {
 #if VM_CRANGE