no need to acquire vmap->lock; seems to work fine without it

589f4656 · Nickolai Zeldovich · f8d394aa · 589f4656
--- a/vm.c
+++ b/vm.c
@@ -650,16 +650,13 @@ copyout(struct vmap *vmap, uint va, void *p, uint len)
  while(len > 0){
    uint va0 = (uint)PGROUNDDOWN(va);
    rcu_begin_read();
-    acquire(&vmap->lock);
    struct vma *vma = vmap_overlap(vmap, va, 1);
    if(vma == 0) {
-      release(&vmap->lock);
      rcu_end_read();
      return -1;
    }

    acquire(&vma->lock);
-    release(&vmap->lock);
    uint pn = (va0 - vma->va_start) / PGSIZE;
    char *p0 = vma->n->page[pn];
    if(p0 == 0)
@@ -684,16 +681,13 @@ copyin(struct vmap *vmap, uint va, void *p, uint len)
  while(len > 0){
    uint va0 = (uint)PGROUNDDOWN(va);
    rcu_begin_read();
-    acquire(&vmap->lock);
    struct vma *vma = vmap_overlap(vmap, va, 1);
    if(vma == 0) {
-      release(&vmap->lock);
      rcu_end_read();
      return -1;
    }

    acquire(&vma->lock);
-    release(&vmap->lock);
    uint pn = (va0 - vma->va_start) / PGSIZE;
    char *p0 = vma->n->page[pn];
    if(p0 == 0)
@@ -721,12 +715,10 @@ pagefault_ondemand(struct vmap *vmap, uint va, uint err, struct vma *m)
  if (vmn_doload(m->n, m->n->ip, m->n->offset, m->n->sz) < 0) {
    panic("pagefault: couldn't load");
  }
-  acquire(&vmap->lock);
  m = vmap_overlap(vmap, va, 1);
  if (!m)
    panic("pagefault_ondemand");
  acquire(&m->lock); // re-acquire lock on m
-  release(&vmap->lock);
  return m;
 }

@@ -761,16 +753,13 @@ pagefault(struct vmap *vmap, uint va, uint err)
    return 0;

  rcu_begin_read();
-  acquire(&vmap->lock);
  struct vma *m = vmap_overlap(vmap, va, 1);
  if(m == 0) {
-    release(&vmap->lock);
    rcu_end_read();
    return -1;
  }

  acquire(&m->lock);
-  release(&vmap->lock);
  uint npg = (PGROUNDDOWN(va) - m->va_start) / PGSIZE;
  if (m->n && m->n->type == ONDEMAND && m->n->page[npg] == 0) {
    m = pagefault_ondemand(vmap, va, err, m);