linux-kernel - [PATCH 1/2][resend] pid: tighten pidmap spinlock critical section by removing kfree()

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Message-Id: <0e91f1c4ecc5bc5000f729ccb56e9b6e1fbd4bd3.1258805412.git.andre.goddard@gmail.com>
Date:	Thu,  3 Dec 2009 12:53:37 -0200
From:	André Goddard Rosa <andre.goddard@...il.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"linux list" <linux-kernel@...r.kernel.org>
Cc:	André Goddard Rosa <andre.goddard@...il.com>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: [PATCH 1/2][resend] pid: tighten pidmap spinlock critical section by removing kfree()

Avoid calling kfree() under pidmap spinlock, calling it afterwards.

Normally kfree() is fast, but sometimes it can be slow, so avoid
calling it under the spinlock if we can do it.

Signed-off-by: André Goddard Rosa <andre.goddard@...il.com>
cc: Pekka Enberg <penberg@...helsinki.fi>
---
 kernel/pid.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/pid.c b/kernel/pid.c
index d3f722d..55fd590 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;
 		}
-- 
1.6.5.3.298.g39add

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