From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754127Ab2DWHKg (ORCPT ); Mon, 23 Apr 2012 03:10:36 -0400 Received: from mail-ob0-f174.google.com ([209.85.214.174]:45494 "EHLO mail-ob0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754002Ab2DWHKc (ORCPT ); Mon, 23 Apr 2012 03:10:32 -0400 Date: Mon, 23 Apr 2012 00:09:15 -0700 From: Anton Vorontsov To: Andrew Morton , Oleg Nesterov Cc: Russell King , Mike Frysinger , Benjamin Herrenschmidt , Richard Weinberger , Paul Mundt , Peter Zijlstra , KOSAKI Motohiro , John Stultz , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, uclinux-dist-devel@blackfin.uclinux.org, linuxppc-dev@lists.ozlabs.org, linux-sh@vger.kernel.org, user-mode-linux-devel@lists.sourceforge.net, linaro-kernel@lists.linaro.org, patches@linaro.org, linux-mm@kvack.org Subject: [PATCH 6/9] blackfin: Fix possible deadlock in decode_address() Message-ID: <20120423070915.GF30752@lizard> References: <20120423070641.GA27702@lizard> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20120423070641.GA27702@lizard> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Oleg Nesterov found an interesting deadlock possibility: > sysrq_showregs_othercpus() does smp_call_function(showacpu) > and showacpu() show_stack()->decode_address(). Now suppose that IPI > interrupts the task holding read_lock(tasklist). To fix this, blackfin should not grab the write_ variant of the tasklist lock, read_ one is enough. Suggested-by: Oleg Nesterov Signed-off-by: Anton Vorontsov --- arch/blackfin/kernel/trace.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/blackfin/kernel/trace.c b/arch/blackfin/kernel/trace.c index d08f0e3..f7f7a18 100644 --- a/arch/blackfin/kernel/trace.c +++ b/arch/blackfin/kernel/trace.c @@ -29,7 +29,7 @@ void decode_address(char *buf, unsigned long address) { struct task_struct *p; struct mm_struct *mm; - unsigned long flags, offset; + unsigned long offset; struct rb_node *n; #ifdef CONFIG_KALLSYMS @@ -113,7 +113,7 @@ void decode_address(char *buf, unsigned long address) * mappings of all our processes and see if we can't be a whee * bit more specific */ - write_lock_irqsave(&tasklist_lock, flags); + read_lock(&tasklist_lock); for_each_process(p) { struct task_struct *t; @@ -186,7 +186,7 @@ __continue: sprintf(buf, "/* kernel dynamic memory */"); done: - write_unlock_irqrestore(&tasklist_lock, flags); + read_unlock(&tasklist_lock); } #define EXPAND_LEN ((1 << CONFIG_DEBUG_BFIN_HWTRACE_EXPAND_LEN) * 256 - 1) -- 1.7.9.2