Serialize vmap::brk_ updates with a spinlock

60a49df9 · Silas Boyd-Wickizer · 26e69730 · 60a49df9 · 60a49df9 · 60a49df9
--- a/include/vm.hh
+++ b/include/vm.hh
@@ -86,7 +86,7 @@ struct vmap {

  int pagefault(uptr va, u32 err);
  int copyout(uptr va, void *p, u64 len);
-  int sbrk(int n);
+  int sbrk(ssize_t n, uptr *addr);

  NEW_DELETE_OPS(vmap)

@@ -94,4 +94,5 @@ struct vmap {

 private:
  int pagefault_wcow(vma *m);
+  struct spinlock brklock_;
 };
--- a/kernel/sysproc.cc
+++ b/kernel/sysproc.cc
@@ -46,8 +46,7 @@ sys_sbrk(int n)
 {
  uptr addr;

-  addr = myproc()->vmap->brk_;
-  if(myproc()->vmap->sbrk(n) < 0)
+  if(myproc()->vmap->sbrk(n, &addr) < 0)
    return -1;
  return addr;
 }

--- a/kernel/vm.cc
+++ b/kernel/vm.cc
@@ -148,6 +148,7 @@ vmap::vmap() :
    ref(1), pml4(setupkvm()), kshared((char*) ksalloc(slab_kshared)),
    brk_(0)
 {
+  initlock(&brklock_, "brk_lock", LOCKSTAT_VM);
  if (pml4 == 0) {
    cprintf("vmap_alloc: setupkvm out of memory\n");
    goto err;
@@ -587,9 +588,11 @@ vmap::copyout(uptr va, void *p, u64 len)
 // Shrinking just decreases proc->brk; doesn't deallocate.
 // Return 0 on success, -1 on failure.
 int
-vmap::sbrk(int n)
+vmap::sbrk(ssize_t n, uptr *addr)
 {
+  scoped_acquire xlock(&brklock_);
  auto curbrk = brk_;
+  *addr = curbrk;

  if(n < 0 && 0 - n <= curbrk){
    brk_ += n;
@@ -626,7 +629,7 @@ vmap::sbrk(int n)
      prev = e;
 #endif
    } else {
-      cprintf("growproc: overlap with existing mapping; brk %lx n %d\n",
+      cprintf("growproc: overlap with existing mapping; brk %lx n %ld\n",
              curbrk, n);
      return -1;
    }