[RFC][v4][PATCH 1/7] Factor out code to allocate pidmap page

[Sukadev Bhattiprolu]

Subject: [RFC][v4][PATCH 1/7] Factor out code to allocate pidmap page

To implement support for clone_with_pids() system call we would
need to allocate pidmap page in more than one place. Move this
code to a new function alloc_pidmap_page().

Changelog[v2]:
	- (Matt Helsley, Dave Hansen) Have alloc_pidmap_page() return
	  -ENOMEM on error instead of -1.

Signed-off-by: Sukadev Bhattiprolu <sukadev at linux.vnet.ibm.com>
Acked-by: Serge Hallyn <serue at us.ibm.com>
Reviewed-by: Oren Laadan <orenl at cs.columbia.edu>
---
 kernel/pid.c |   46 ++++++++++++++++++++++++++++++----------------
 1 files changed, 30 insertions(+), 16 deletions(-)

Index: linux-2.6/kernel/pid.c
===================================================================
--- linux-2.6.orig/kernel/pid.c	2009-08-05 17:00:22.000000000 -0700
+++ linux-2.6/kernel/pid.c	2009-08-05 17:02:40.000000000 -0700
@@ -122,9 +122,34 @@
 	atomic_inc(&map->nr_free);
 }
 
+static int alloc_pidmap_page(struct pidmap *map)
+{
+	void *page;
+
+	if (likely(map->page))
+		return 0;
+
+	page = kzalloc(PAGE_SIZE, GFP_KERNEL);
+
+	/*
+	 * Free the page if someone raced with us installing it:
+	 */
+	spin_lock_irq(&pidmap_lock);
+	if (map->page)
+		kfree(page);
+	else
+		map->page = page;
+	spin_unlock_irq(&pidmap_lock);
+
+	if (unlikely(!map->page))
+		return -ENOMEM;
+
+	return 0;
+}
+
 static int alloc_pidmap(struct pid_namespace *pid_ns)
 {
-	int i, offset, max_scan, pid, last = pid_ns->last_pid;
+	int i, rc, offset, max_scan, pid, last = pid_ns->last_pid;
 	struct pidmap *map;
 
 	pid = last + 1;
@@ -134,21 +159,10 @@
 	map = &pid_ns->pidmap[pid/BITS_PER_PAGE];
 	max_scan = (pid_max + BITS_PER_PAGE - 1)/BITS_PER_PAGE - !offset;
 	for (i = 0; i <= max_scan; ++i) {
-		if (unlikely(!map->page)) {
-			void *page = kzalloc(PAGE_SIZE, GFP_KERNEL);
-			/*
-			 * Free the page if someone raced with us
-			 * installing it:
-			 */
-			spin_lock_irq(&pidmap_lock);
-			if (map->page)
-				kfree(page);
-			else
-				map->page = page;
-			spin_unlock_irq(&pidmap_lock);
-			if (unlikely(!map->page))
-				break;
-		}
+		rc = alloc_pidmap_page(map);
+		if (rc)
+			break;
+
 		if (likely(atomic_read(&map->nr_free))) {
 			do {
 				if (!test_and_set_bit(offset, map->page)) {