Re: /proc/sys/kernel/pid_max issues

[William Lee Irwin III <wli@holomorphy.com>]

On Sun, Sep 12, 2004 at 03:43:14AM -0700, William Lee Irwin III wrote:
>> I like the update. But I see other issues. For instance (also untested):
>> pid wrapping doesn't honor RESERVED_PIDS.

On Sun, Sep 12, 2004 at 03:45:24AM -0700, William Lee Irwin III wrote:
> last_pid is not honored because next_free_map(map - 1, ...) may return
> the same map and so restart with a lesser offset.

Forgot to check map->page in the first spin:

last_pid is not honored because next_free_map(map - 1, ...) may return
the same map and so restart with a lesser offset.

Index: mm4-2.6.9-rc1/kernel/pid.c
===================================================================
--- mm4-2.6.9-rc1.orig/kernel/pid.c	2004-09-12 03:26:50.063164288 -0700
+++ mm4-2.6.9-rc1/kernel/pid.c	2004-09-12 04:00:03.230156848 -0700
@@ -64,6 +64,21 @@
 	atomic_inc(&map->nr_free);
 }
 
+static void alloc_pidmap_page(pidmap_t *map)
+{
+	unsigned long page = get_zeroed_page(GFP_KERNEL);
+	/*
+	 * Free the page if someone raced with us
+	 * installing it:
+	 */
+	spin_lock(&pidmap_lock);
+	if (map->page)
+		free_page(page);
+	else
+		map->page = (void *)page;
+	spin_unlock(&pidmap_lock);
+}
+
 /*
  * Here we search for the next map that has free bits left.
  * Normally the next map has free PIDs.
@@ -76,18 +91,7 @@
 		if (++map > map_limit)
 			map = pidmap_array;
 		if (unlikely(!map->page)) {
-			unsigned long page = get_zeroed_page(GFP_KERNEL);
-			/*
-			 * Free the page if someone raced with us
-			 * installing it:
-			 */
-			spin_lock(&pidmap_lock);
-			if (map->page)
-				free_page(page);
-			else
-				map->page = (void *)page;
-			spin_unlock(&pidmap_lock);
-
+			alloc_pidmap_page(map);
 			if (!map->page)
 				break;
 		}
@@ -119,11 +123,20 @@
 		atomic_dec(&map->nr_free);
 		last_pid = pid;
 		return pid;
-	}
-	
-	if (!offset || !atomic_read(&map->nr_free)) {
-		if (!offset)
-			map--;
+	} else if (!offset) {
+		if (map->page) {
+			if (atomic_read(&map->nr_free))
+				goto scan_more;
+			else
+				goto next_map;
+		} else {
+			alloc_pidmap_page(map);
+			if (map->page)
+				goto scan_more;
+			else
+				goto failure;
+		}
+	} else if (!atomic_read(&map->nr_free)) {
 next_map:
 		map = next_free_map(map, &max_steps);
 		if (!map)