From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-bk0-f51.google.com (mail-bk0-f51.google.com [209.85.214.51]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority" (not verified)) by ozlabs.org (Postfix) with ESMTPS id F2A56B6EEC for ; Sat, 24 Mar 2012 21:31:19 +1100 (EST) Received: by mail-bk0-f51.google.com with SMTP id j10so3226820bkw.38 for ; Sat, 24 Mar 2012 03:31:19 -0700 (PDT) Date: Sat, 24 Mar 2012 14:30:08 +0400 From: Anton Vorontsov To: Andrew Morton , Oleg Nesterov Subject: [PATCH 06/10] blackfin: Fix possible deadlock in decode_address() Message-ID: <20120324103008.GF29067@lizard> References: <20120324102609.GA28356@lizard> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 In-Reply-To: <20120324102609.GA28356@lizard> Cc: Mike Frysinger , Peter Zijlstra , user-mode-linux-devel@lists.sourceforge.net, linux-sh@vger.kernel.org, Richard Weinberger , linux-kernel@vger.kernel.org, uclinux-dist-devel@blackfin.uclinux.org, linux-mm@kvack.org, Paul Mundt , John Stultz , KOSAKI Motohiro , Russell King , linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 5102cdf..9cc9302 100644 --- a/arch/blackfin/kernel/trace.c +++ b/arch/blackfin/kernel/trace.c @@ -28,7 +28,7 @@ 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 @@ -112,7 +112,7 @@ 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; @@ -185,7 +185,7 @@ __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