linux-kernel - [PATCH] kprobes: Sanitize struct kretprobe

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Message-ID: <20091030135310.GA22230@in.ibm.com>
Date:	Fri, 30 Oct 2009 19:23:10 +0530
From:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
To:	lkml <linux-kernel@...r.kernel.org>
Cc:	Masami Hiramatsu <mhiramat@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jim Keniston <jkenisto@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>, fweisbec@...il.com
Subject: [PATCH] kprobes: Sanitize struct kretprobe_instance allocations

From: Ananth N Mavinakayanahalli <ananth@...ibm.com>

For as long as kretprobes have existed, we've allocated NR_CPUS
instances of kretprobe_instance structures. With the default value of
CONFIG_NR_CPUS increasing on certain architectures, we are potentially
wasting kernel memory.

See http://sourceware.org/bugzilla/show_bug.cgi?id=10839#c3 for more
details.

Use a saner num_possible_cpus() instead of NR_CPUS for allocation.

Signed-off-by: Ananth N Mavinakayanahalli <ananth@...ibm.com>
---
 kernel/kprobes.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Index: linux-2.6.32-rc5/kernel/kprobes.c
===================================================================
--- linux-2.6.32-rc5.orig/kernel/kprobes.c
+++ linux-2.6.32-rc5/kernel/kprobes.c
@@ -1014,9 +1014,9 @@ int __kprobes register_kretprobe(struct 
 	/* Pre-allocate memory for max kretprobe instances */
 	if (rp->maxactive <= 0) {
 #ifdef CONFIG_PREEMPT
-		rp->maxactive = max(10, 2 * NR_CPUS);
+		rp->maxactive = max(10, 2 * num_possible_cpus());
 #else
-		rp->maxactive = NR_CPUS;
+		rp->maxactive = num_possible_cpus();
 #endif
 	}
 	spin_lock_init(&rp->lock);
--
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