linux-kernel - [PATCH] pid: tighten pidmap

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Date:	Sat, 21 Nov 2009 04:04:34 -0200
From:	André Goddard Rosa <andre.goddard@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Oleg Nesterov <oleg@...hat.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Jiri Kosina <jkosina@...e.cz>, linux-kernel@...r.kernel.org
Cc:	André Goddard Rosa <andre.goddard@...il.com>
Subject: [PATCH] pid: tighten pidmap_lock critical section

Avoid calling kfree() under pidmap_lock and doing unnecessary work.
It doesn't change behavior.

It decreases code size by 16 bytes on my gcc 4.4.1 on Core 2:
   text    data     bss     dec     hex filename
   4314    2216       8    6538    198a kernel/pid.o-BEFORE
   4298    2216       8    6522    197a kernel/pid.o-AFTER

Signed-off-by: André Goddard Rosa <andre.goddard@...il.com>
---
 kernel/pid.c |   16 ++++++++--------
 1 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/kernel/pid.c b/kernel/pid.c
index d3f722d..ec06912 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -141,11 +141,12 @@ static int alloc_pidmap(struct pid_namespace *pid_ns)
 			 * installing it:
 			 */
 			spin_lock_irq(&pidmap_lock);
-			if (map->page)
-				kfree(page);
-			else
+			if (!map->page) {
 				map->page = page;
+				page = NULL;
+			}
 			spin_unlock_irq(&pidmap_lock);
+			kfree(page);
 			if (unlikely(!map->page))
 				break;
 		}
@@ -225,11 +226,11 @@ static void delayed_put_pid(struct rcu_head *rhp)
 void free_pid(struct pid *pid)
 {
 	/* We can be called with write_lock_irq(&tasklist_lock) held */
-	int i;
+	int i = 0;
 	unsigned long flags;
 
 	spin_lock_irqsave(&pidmap_lock, flags);
-	for (i = 0; i <= pid->level; i++)
+	for ( ; i <= pid->level; i++)
 		hlist_del_rcu(&pid->numbers[i].pid_chain);
 	spin_unlock_irqrestore(&pidmap_lock, flags);
 
@@ -268,12 +269,11 @@ struct pid *alloc_pid(struct pid_namespace *ns)
 	for (type = 0; type < PIDTYPE_MAX; ++type)
 		INIT_HLIST_HEAD(&pid->tasks[type]);
 
+	upid = pid->numbers + ns->level;
 	spin_lock_irq(&pidmap_lock);
-	for (i = ns->level; i >= 0; i--) {
-		upid = &pid->numbers[i];
+	for ( ; upid >= pid->numbers; --upid)
 		hlist_add_head_rcu(&upid->pid_chain,
 				&pid_hash[pid_hashfn(upid->nr, upid->ns)]);
-	}
 	spin_unlock_irq(&pidmap_lock);
 
 out:
-- 
1.6.5.3.148.g785c5

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