From d67371dab632a5e4198509966ecf2519692abdc4 Mon Sep 17 00:00:00 2001
From: attilio <attilio@FreeBSD.org>
Date: Mon, 8 Apr 2013 19:58:32 +0000
Subject: [PATCH] Switch some "low-hanging fruit" to acquire read lock on
 vmobjects rather than write locks.

Sponsored by:	EMC / Isilon storage division
Reviewed by:	alc
Tested by:	pho
---
 sys/kern/imgact_elf.c  |  8 ++++----
 sys/kern/kern_proc.c   | 20 ++++++++++----------
 sys/kern/sys_process.c | 10 +++++-----
 3 files changed, 19 insertions(+), 19 deletions(-)

diff --git a/sys/kern/imgact_elf.c b/sys/kern/imgact_elf.c
index 28ff189c255b..813e37a559e8 100644
--- a/sys/kern/imgact_elf.c
+++ b/sys/kern/imgact_elf.c
@@ -1277,15 +1277,15 @@ each_writable_segment(td, func, closure)
 			continue;
 
 		/* Ignore memory-mapped devices and such things. */
-		VM_OBJECT_WLOCK(object);
+		VM_OBJECT_RLOCK(object);
 		while ((backing_object = object->backing_object) != NULL) {
-			VM_OBJECT_WLOCK(backing_object);
-			VM_OBJECT_WUNLOCK(object);
+			VM_OBJECT_RLOCK(backing_object);
+			VM_OBJECT_RUNLOCK(object);
 			object = backing_object;
 		}
 		ignore_entry = object->type != OBJT_DEFAULT &&
 		    object->type != OBJT_SWAP && object->type != OBJT_VNODE;
-		VM_OBJECT_WUNLOCK(object);
+		VM_OBJECT_RUNLOCK(object);
 		if (ignore_entry)
 			continue;
 
diff --git a/sys/kern/kern_proc.c b/sys/kern/kern_proc.c
index 6c46801fb8e7..e3f321125a3b 100644
--- a/sys/kern/kern_proc.c
+++ b/sys/kern/kern_proc.c
@@ -1995,7 +1995,7 @@ sysctl_kern_proc_ovmmap(SYSCTL_HANDLER_ARGS)
 		kve->kve_private_resident = 0;
 		obj = entry->object.vm_object;
 		if (obj != NULL) {
-			VM_OBJECT_WLOCK(obj);
+			VM_OBJECT_RLOCK(obj);
 			if (obj->shadow_count == 1)
 				kve->kve_private_resident =
 				    obj->resident_page_count;
@@ -2010,9 +2010,9 @@ sysctl_kern_proc_ovmmap(SYSCTL_HANDLER_ARGS)
 
 		for (lobj = tobj = obj; tobj; tobj = tobj->backing_object) {
 			if (tobj != obj)
-				VM_OBJECT_WLOCK(tobj);
+				VM_OBJECT_RLOCK(tobj);
 			if (lobj != obj)
-				VM_OBJECT_WUNLOCK(lobj);
+				VM_OBJECT_RUNLOCK(lobj);
 			lobj = tobj;
 		}
 
@@ -2072,11 +2072,11 @@ sysctl_kern_proc_ovmmap(SYSCTL_HANDLER_ARGS)
 				break;
 			}
 			if (lobj != obj)
-				VM_OBJECT_WUNLOCK(lobj);
+				VM_OBJECT_RUNLOCK(lobj);
 
 			kve->kve_ref_count = obj->ref_count;
 			kve->kve_shadow_count = obj->shadow_count;
-			VM_OBJECT_WUNLOCK(obj);
+			VM_OBJECT_RUNLOCK(obj);
 			if (vp != NULL) {
 				vn_fullpath(curthread, vp, &fullpath,
 				    &freepath);
@@ -2162,7 +2162,7 @@ sysctl_kern_proc_vmmap(SYSCTL_HANDLER_ARGS)
 		kve->kve_private_resident = 0;
 		obj = entry->object.vm_object;
 		if (obj != NULL) {
-			VM_OBJECT_WLOCK(obj);
+			VM_OBJECT_RLOCK(obj);
 			if (obj->shadow_count == 1)
 				kve->kve_private_resident =
 				    obj->resident_page_count;
@@ -2183,9 +2183,9 @@ sysctl_kern_proc_vmmap(SYSCTL_HANDLER_ARGS)
 
 		for (lobj = tobj = obj; tobj; tobj = tobj->backing_object) {
 			if (tobj != obj)
-				VM_OBJECT_WLOCK(tobj);
+				VM_OBJECT_RLOCK(tobj);
 			if (lobj != obj)
-				VM_OBJECT_WUNLOCK(lobj);
+				VM_OBJECT_RUNLOCK(lobj);
 			lobj = tobj;
 		}
 
@@ -2247,11 +2247,11 @@ sysctl_kern_proc_vmmap(SYSCTL_HANDLER_ARGS)
 				break;
 			}
 			if (lobj != obj)
-				VM_OBJECT_WUNLOCK(lobj);
+				VM_OBJECT_RUNLOCK(lobj);
 
 			kve->kve_ref_count = obj->ref_count;
 			kve->kve_shadow_count = obj->shadow_count;
-			VM_OBJECT_WUNLOCK(obj);
+			VM_OBJECT_RUNLOCK(obj);
 			if (vp != NULL) {
 				vn_fullpath(curthread, vp, &fullpath,
 				    &freepath);
diff --git a/sys/kern/sys_process.c b/sys/kern/sys_process.c
index 7dc43c43cff8..5508dcff15fb 100644
--- a/sys/kern/sys_process.c
+++ b/sys/kern/sys_process.c
@@ -382,7 +382,7 @@ ptrace_vm_entry(struct thread *td, struct proc *p, struct ptrace_vm_entry *pve)
 
 		obj = entry->object.vm_object;
 		if (obj != NULL)
-			VM_OBJECT_WLOCK(obj);
+			VM_OBJECT_RLOCK(obj);
 	} while (0);
 
 	vm_map_unlock_read(map);
@@ -395,9 +395,9 @@ ptrace_vm_entry(struct thread *td, struct proc *p, struct ptrace_vm_entry *pve)
 		lobj = obj;
 		for (tobj = obj; tobj != NULL; tobj = tobj->backing_object) {
 			if (tobj != obj)
-				VM_OBJECT_WLOCK(tobj);
+				VM_OBJECT_RLOCK(tobj);
 			if (lobj != obj)
-				VM_OBJECT_WUNLOCK(lobj);
+				VM_OBJECT_RUNLOCK(lobj);
 			lobj = tobj;
 			pve->pve_offset += tobj->backing_object_offset;
 		}
@@ -405,8 +405,8 @@ ptrace_vm_entry(struct thread *td, struct proc *p, struct ptrace_vm_entry *pve)
 		if (vp != NULL)
 			vref(vp);
 		if (lobj != obj)
-			VM_OBJECT_WUNLOCK(lobj);
-		VM_OBJECT_WUNLOCK(obj);
+			VM_OBJECT_RUNLOCK(lobj);
+		VM_OBJECT_RUNLOCK(obj);
 
 		if (vp != NULL) {
 			freepath = NULL;