From mboxrd@z Thu Jan 1 00:00:00 1970 From: Santosh Shilimkar Subject: Re: [PATCH] power: opp: Fix rcu_dereference_check() without protection! Date: Wed, 15 Jun 2011 11:50:33 +0530 Message-ID: <4DF84F31.4030108@ti.com> References: <1308056600-17601-1-git-send-email-santosh.shilimkar@ti.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from na3sys009aog116.obsmtp.com ([74.125.149.240]:59497 "EHLO na3sys009aog116.obsmtp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750887Ab1FOGUk (ORCPT ); Wed, 15 Jun 2011 02:20:40 -0400 In-Reply-To: Sender: linux-omap-owner@vger.kernel.org List-Id: linux-omap@vger.kernel.org To: "Menon, Nishanth" Cc: linux-pm@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linux-omap@vger.kernel.org, "Rafael J. Wysocki" , Kevin Hilman On 6/14/2011 9:08 PM, Menon, Nishanth wrote: > On Tue, Jun 14, 2011 at 08:03, Santosh Shilimkar > wrote: >> With RCU debug options enabled, below warning is observed. >> >> =================================================== >> [ INFO: suspicious rcu_dereference_check() usage. ] >> --------------------------------------------------- >> drivers/base/power/opp.c:151 invoked rcu_dereference_check() without protection! >> >> other info that might help us debug this: >> >> rcu_scheduler_active = 1, debug_locks = 1 >> no locks held by swapper/1. >> ... >> >> --------------------------------------------------- >> >> Fix the same by protecting it with rcu_read lock. >> >> Signed-off-by: Santosh Shilimkar >> Cc: Rafael J. Wysocki >> Cc: Nishanth Menon >> Cc: Kevin Hilman >> --- >> drivers/base/power/opp.c | 2 ++ >> 1 files changed, 2 insertions(+), 0 deletions(-) >> >> diff --git a/drivers/base/power/opp.c b/drivers/base/power/opp.c >> index 56a6899..cbed5e1 100644 >> --- a/drivers/base/power/opp.c >> +++ b/drivers/base/power/opp.c >> @@ -148,7 +148,9 @@ unsigned long opp_get_voltage(struct opp *opp) >> struct opp *tmp_opp; >> unsigned long v = 0; >> >> + rcu_read_lock(); >> tmp_opp = rcu_dereference(opp); >> + rcu_read_unlock(); >> if (unlikely(IS_ERR_OR_NULL(tmp_opp)) || !tmp_opp->available) >> pr_err("%s: Invalid parameters\n", __func__); >> else > NAK. please read the Documentation/power/opp.txt > the usage is as follows: > rcu_read_lock(); > opp = opp_find_freq_ceil(); > voltage = opp_get_voltage(opp); > rcu_read_unlock(); > > the reason for this is that the opp pointer is not safe if we lock > just the dereferencing. > Fair enough. if the whole fn is under the lock then it's not necessary. Regards Santosh