- Make the acquisition of Giant in vm_fault_unwire() conditional on the

   pmap.  For the kernel pmap, Giant is not required.  In general, for
   other pmaps, Giant is required by i386's pmap_pte() implementation.
   Specifically, the use of PMAP2/PADDR2 is synchronized by Giant.
   Note: In principle, updates to the kernel pmap's wired count could be
   lost without Giant.  However, in practice, we never use the kernel
   pmap's wired count.  This will be resolved when pmap locking appears.
 - With the above change, cpu_thread_clean() and uma_large_free() need
   not acquire Giant.  (The first case is simply the revival of
   i386/i386/vm_machdep.c's revision 1.226 by peter.)

3 files changed, 5 insertions, 15 deletions

diff --git a/sys/i386/i386/vm_machdep.c b/sys/i386/i386/vm_machdep.c
index b09128d..e9e236f 100644
--- a/sys/i386/i386/vm_machdep.c
+++ b/sys/i386/i386/vm_machdep.c
@@ -320,10 +320,8 @@ cpu_thread_clean(struct thread *td)
 		 * XXX do we need to move the TSS off the allocated pages
 		 * before freeing them?  (not done here)
 		 */
-		mtx_lock(&Giant);
 		kmem_free(kernel_map, (vm_offset_t)pcb->pcb_ext,
 		    ctob(IOPAGES + 1));
-		mtx_unlock(&Giant);
 		pcb->pcb_ext = 0;
 	}
 }
diff --git a/sys/vm/uma_core.c b/sys/vm/uma_core.c
index fb5f5fc..f693540 100644
--- a/sys/vm/uma_core.c
+++ b/sys/vm/uma_core.c
@@ -2052,17 +2052,7 @@ void
 uma_large_free(uma_slab_t slab)
 {
 	vsetobj((vm_offset_t)slab->us_data, kmem_object);
-	/*
-	 * XXX: We get a lock order reversal if we don't have Giant:
-	 * vm_map_remove (locks system map) -> vm_map_delete ->
-	 *    vm_map_entry_unwire -> vm_fault_unwire -> mtx_lock(&Giant)
-	 */
-	if (!mtx_owned(&Giant)) {
-		mtx_lock(&Giant);
-		page_free(slab->us_data, slab->us_size, slab->us_flags);
-		mtx_unlock(&Giant);
-	} else
-		page_free(slab->us_data, slab->us_size, slab->us_flags);
+	page_free(slab->us_data, slab->us_size, slab->us_flags);
 	uma_zfree_internal(slabzone, slab, NULL, 0);
 }
 
diff --git a/sys/vm/vm_fault.c b/sys/vm/vm_fault.c
index 602b659..fded099 100644
--- a/sys/vm/vm_fault.c
+++ b/sys/vm/vm_fault.c
@@ -1081,7 +1081,8 @@ vm_fault_unwire(map, start, end)
 
 	pmap = vm_map_pmap(map);
 
-	mtx_lock(&Giant);
+	if (pmap != kernel_pmap)
+		mtx_lock(&Giant);
 	/*
 	 * Since the pages are wired down, we must be able to get their
 	 * mappings from the physical map system.
@@ -1095,7 +1096,8 @@ vm_fault_unwire(map, start, end)
 			vm_page_unlock_queues();
 		}
 	}
-	mtx_unlock(&Giant);
+	if (pmap != kernel_pmap)
+		mtx_unlock(&Giant);
 }
 
 /*