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

Sukadev Bhattiprolu
2009-08-07T06:12:05Z

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@linux.vnet.ibm.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Reviewed-by: Oren Laadan <orenl@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)) {