Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754527Ab1EYGej (ORCPT ); Wed, 25 May 2011 02:34:39 -0400 Received: from mail4.comsite.net ([205.238.176.238]:9433 "EHLO mail4.comsite.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754240Ab1EYGeg (ORCPT ); Wed, 25 May 2011 02:34:36 -0400 X-Default-Received-SPF: pass (skip=forwardok (res=PASS)) x-ip-name=71.22.127.106; Subject: [PATCH 1/4] sparse irq: protect irq_to_desc against irq_free_descs From: Milton Miller Message-Id: In-Reply-To: References: To: Thomas Gleixner Cc: , "Paul E. McKenney" Date: Wed, 25 May 2011 01:34:18 -0500 X-Originating-IP: 71.22.127.106 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2140 Lines: 52 The radix-tree code uses call_rcu to delay freeing internal data elements when removing when deleting an entry. We must protect against the elements being freed while we traverse the tree. While preparing a patch to expand the contexts in which the radix tree optionally used by powerpc for mapping hardware irq numbers to linux numbers would be called, I realized that the radix tree was not locked when radix_tree_lookup was called. I then realized the same issue applies to the generic irq code when sparse irqs are in use. While the powerpc radix tree was only referenced from one callsite that was irqs_disabled and irq_enter, irq_to_desc is called from many more contexts including threaded irq handlers and other process contexts. This does not show up in the rcu lockdep because in 2.6.34 commit 2676a58c98 (radix-tree: Disable RCU lockdep checking in radix tree) deemed it too hard to pass the condition of the protecting lock to the library. Signed-off-by: Milton Miller Cc: --- I expect the relatively infrequent calls to irq_free_descs, combined with most calls to irq_to_desc being irqs_disabled and the fact merged to mainline implemntations of call_rcu requiring a cpu to respond to a hard irq or schedule has hidden this error to date. Index: work.git/kernel/irq/irqdesc.c =================================================================== --- work.git.orig/kernel/irq/irqdesc.c 2011-05-23 13:34:08.728585785 -0500 +++ work.git/kernel/irq/irqdesc.c 2011-05-23 13:46:09.197635762 -0500 @@ -108,7 +108,13 @@ static void irq_insert_desc(unsigned int struct irq_desc *irq_to_desc(unsigned int irq) { - return radix_tree_lookup(&irq_desc_tree, irq); + struct irq_desc *desc; + + rcu_read_lock(); + desc = radix_tree_lookup(&irq_desc_tree, irq); + rcu_read_unlock(); + + return desc } static void delete_irq_desc(unsigned int irq) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/