[PATCH 3/3 gnumach] kern/gsync: Use vm_map_lookup with exit_map_locked as appropriate

[Damien Zammit]

This refactors gsync functions so that the read lock on vm map
is only taken once and extended throughout appropriate calls.

Co-Authored-By: Sergey Bugaev <buga...@gmail.com>
---
 kern/gsync.c | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/kern/gsync.c b/kern/gsync.c
index 19190349..083f90b9 100644
--- a/kern/gsync.c
+++ b/kern/gsync.c
@@ -126,7 +126,7 @@ gsync_key_hash (const union gsync_key *keyp)
  * in VAP. Returns 0 if successful, -1 otherwise. */
 static int
 probe_address (vm_map_t map, vm_offset_t addr,
-  int flags, struct vm_args *vap)
+  int flags, boolean_t exit_map_locked, struct vm_args *vap)
 {
   vm_prot_t prot = VM_PROT_READ |
     ((flags & GSYNC_MUTATE) ? VM_PROT_WRITE : 0);
@@ -134,11 +134,17 @@ probe_address (vm_map_t map, vm_offset_t addr,
   vm_prot_t rprot;
   boolean_t wired_p;
 
-  if (vm_map_lookup (&map, addr, prot, FALSE, &ver,
+  if (vm_map_lookup (&map, addr, prot, exit_map_locked, &ver,
       &vap->obj, &vap->off, &rprot, &wired_p) != KERN_SUCCESS)
-    return (-1);
+    {
+      if (exit_map_locked)
+        vm_map_unlock_read (map);
+      return (-1);
+    }
   else if ((rprot & prot) != prot)
     {
+      if (exit_map_locked)
+        vm_map_unlock_read (map);
       vm_object_unlock (vap->obj);
       return (-1);
     }
@@ -151,9 +157,9 @@ probe_address (vm_map_t map, vm_offset_t addr,
  * the argument VAP for future use. */
 static int
 gsync_prepare_key (task_t task, vm_offset_t addr, int flags,
-  union gsync_key *keyp, struct vm_args *vap)
+  boolean_t exit_map_locked, union gsync_key *keyp, struct vm_args *vap)
 {
-  if (probe_address (task->map, addr, flags, vap) < 0)
+  if (probe_address (task->map, addr, flags, exit_map_locked, vap) < 0)
     return (-1);
   else if (flags & GSYNC_SHARED)
     {
@@ -227,12 +233,10 @@ kern_return_t gsync_wait (task_t task, vm_offset_t addr,
   else if (addr % sizeof (int) != 0)
     return (KERN_INVALID_ADDRESS);
 
-  vm_map_lock_read (task->map);
-
   struct gsync_waiter w;
   struct vm_args va;
   boolean_t remote = task != current_task ();
-  int bucket = gsync_prepare_key (task, addr, flags, &w.key, &va);
+  int bucket = gsync_prepare_key (task, addr, flags, TRUE, &w.key, &va);
 
   if (bucket < 0)
     {
@@ -354,11 +358,9 @@ kern_return_t gsync_wake (task_t task,
   else if (addr % sizeof (int) != 0)
     return (KERN_INVALID_ADDRESS);
 
-  vm_map_lock_read (task->map);
-
   union gsync_key key;
   struct vm_args va;
-  int bucket = gsync_prepare_key (task, addr, flags, &key, &va);
+  int bucket = gsync_prepare_key (task, addr, flags, TRUE, &key, &va);
 
   if (bucket < 0)
     {
@@ -434,14 +436,14 @@ kern_return_t gsync_requeue (task_t task, vm_offset_t src,
   union gsync_key src_k, dst_k;
   struct vm_args va;
 
-  int src_bkt = gsync_prepare_key (task, src, flags, &src_k, &va);
+  int src_bkt = gsync_prepare_key (task, src, flags, FALSE, &src_k, &va);
   if (src_bkt < 0)
     return (KERN_INVALID_ADDRESS);
 
   /* Unlock the VM object before the second lookup. */
   vm_object_unlock (va.obj);
 
-  int dst_bkt = gsync_prepare_key (task, dst, flags, &dst_k, &va);
+  int dst_bkt = gsync_prepare_key (task, dst, flags, FALSE, &dst_k, &va);
   if (dst_bkt < 0)
     return (KERN_INVALID_ADDRESS);
 
-- 
2.43.0