From 9e829b2272a8258a0e148e38e08697f07a0267fc Mon Sep 17 00:00:00 2001
From: Alan Cox <alc@FreeBSD.org>
Date: Sat, 26 Sep 2015 22:57:10 +0000
Subject: [PATCH] The conversion of kmem_alloc_attr() from operating on a vm
 map to a vmem arena in r254025 introduced a bug in the case when an
 allocation is only partially successful.  Specifically, the vm object lock
 was not being acquired before freeing the allocated pages.  To address this
 bug, replace the existing code by a call to kmem_unback().

Change the type of a variable in kmem_alloc_attr() so that an allocation
of two or more gigabytes won't fail.

Replace the error handling code in kmem_back() by a call to kmem_unback().

Reviewed by:	kib (an earlier version)
MFC after:	1 week
Sponsored by:	EMC / Isilon Storage Division
---
 sys/vm/vm_kern.c | 41 +++++++++++++----------------------------
 1 file changed, 13 insertions(+), 28 deletions(-)

diff --git a/sys/vm/vm_kern.c b/sys/vm/vm_kern.c
index fd16bf217b59..f0aacf11a1c7 100644
--- a/sys/vm/vm_kern.c
+++ b/sys/vm/vm_kern.c
@@ -159,11 +159,10 @@ kmem_alloc_attr(vmem_t *vmem, vm_size_t size, int flags, vm_paddr_t low,
     vm_paddr_t high, vm_memattr_t memattr)
 {
 	vm_object_t object = vmem == kmem_arena ? kmem_object : kernel_object;
-	vm_offset_t addr;
+	vm_offset_t addr, i;
 	vm_ooffset_t offset;
 	vm_page_t m;
 	int pflags, tries;
-	int i;
 
 	size = round_page(size);
 	if (vmem_alloc(vmem, size, M_BESTFIT | flags, &addr))
@@ -184,18 +183,7 @@ kmem_alloc_attr(vmem_t *vmem, vm_size_t size, int flags, vm_paddr_t low,
 				tries++;
 				goto retry;
 			}
-			/* 
-			 * Unmap and free the pages.
-			 */
-			if (i != 0)
-				pmap_remove(kernel_pmap, addr, addr + i);
-			while (i != 0) {
-				i -= PAGE_SIZE;
-				m = vm_page_lookup(object,
-				    OFF_TO_IDX(offset + i));
-				vm_page_unwire(m, PQ_INACTIVE);
-				vm_page_free(m);
-			}
+			kmem_unback(object, addr, i);
 			vmem_free(vmem, addr, size);
 			return (0);
 		}
@@ -353,25 +341,13 @@ kmem_back(vm_object_t object, vm_offset_t addr, vm_size_t size, int flags)
 		 * aren't on any queues.
 		 */
 		if (m == NULL) {
+			VM_OBJECT_WUNLOCK(object);
 			if ((flags & M_NOWAIT) == 0) {
-				VM_OBJECT_WUNLOCK(object);
 				VM_WAIT;
 				VM_OBJECT_WLOCK(object);
 				goto retry;
 			}
-			/* 
-			 * Unmap and free the pages.
-			 */
-			if (i != 0)
-				pmap_remove(kernel_pmap, addr, addr + i);
-			while (i != 0) {
-				i -= PAGE_SIZE;
-				m = vm_page_lookup(object,
-						   OFF_TO_IDX(offset + i));
-				vm_page_unwire(m, PQ_INACTIVE);
-				vm_page_free(m);
-			}
-			VM_OBJECT_WUNLOCK(object);
+			kmem_unback(object, addr, i);
 			return (KERN_NO_SPACE);
 		}
 		if (flags & M_ZERO && (m->flags & PG_ZERO) == 0)
@@ -387,6 +363,15 @@ kmem_back(vm_object_t object, vm_offset_t addr, vm_size_t size, int flags)
 	return (KERN_SUCCESS);
 }
 
+/*
+ *	kmem_unback:
+ *
+ *	Unmap and free the physical pages underlying the specified virtual
+ *	address range.
+ *
+ *	A physical page must exist within the specified object at each index
+ *	that is being unmapped.
+ */
 void
 kmem_unback(vm_object_t object, vm_offset_t addr, vm_size_t size)
 {