Return-path: Received: from mga02.intel.com ([134.134.136.20]:54938 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932171AbZHFUP6 (ORCPT ); Thu, 6 Aug 2009 16:15:58 -0400 Subject: Re: [PATCH 2.6.30] iwl3945: fix rfkill switch From: reinette chatre To: Stanislaw Gruszka Cc: "linux-wireless@vger.kernel.org" , "Zhu, Yi" , "John W. Linville" , "stable@kernel.org" In-Reply-To: <20090806071902.GA9816@dhcp-lab-161.englab.brq.redhat.com> References: <1249389350-4158-1-git-send-email-sgruszka@redhat.com> <1249512709.30019.4902.camel@rc-desk> <20090806071902.GA9816@dhcp-lab-161.englab.brq.redhat.com> Content-Type: text/plain Date: Thu, 06 Aug 2009 13:15:58 -0700 Message-Id: <1249589758.30019.5034.camel@rc-desk> Mime-Version: 1.0 Sender: linux-wireless-owner@vger.kernel.org List-ID: Hi Stanislaw, On Thu, 2009-08-06 at 00:19 -0700, Stanislaw Gruszka wrote: > On Wed, Aug 05, 2009 at 03:51:49PM -0700, reinette chatre wrote: > > On Tue, 2009-08-04 at 05:35 -0700, Stanislaw Gruszka wrote: > > > Due to rfkill and iwlwifi mishmash of SW / HW killswitch representation, > > > we have race conditions which make unable turn wifi radio on, after enable > > > and disable again killswitch. I can observe this problem on my laptop > > > with iwl3945 device. > > > > > > In rfkill core HW switch and SW switch are separate 'states'. Device can > > > be only in one of 3 states: RFKILL_STATE_SOFT_BLOCKED, RFKILL_STATE_UNBLOCKED, > > > RFKILL_STATE_HARD_BLOCKED. Whereas in iwlwifi driver we have separate bits > > > STATUS_RF_KILL_HW and STATUS_RF_KILL_SW for HW and SW switches - radio can be > > > turned on, only if both bits are cleared. > > > > > > In this particular race conditions, radio can not be turned on if in driver > > > STATUS_RF_KILL_SW bit is set, and rfkill core is in state > > > RFKILL_STATE_HARD_BLOCKED, because rfkill core is unable to call > > > rfkill->toggle_radio(). This situation can be entered in case: > > > > > > > I am trying to understand this race condition ... > > > > > - killswitch is turned on > > > - rfkill core 'see' button change first and move to RFKILL_STATE_SOFT_BLOCKED > > > also call ->toggle_radio() and STATE_RF_KILL_SW in driver is set > > > - iwl3945 get info about button from hardware to set STATUS_RF_KILL_HW bit and > > > force rfkill to move to RFKILL_STATE_HARD_BLOCKED > > > > ok - so at this point we have rfkill == RFKILL_STATE_HARD_BLOCKED, and > > driver == STATE_RF_KILL_SW | STATE_RF_KILL_HW > > > > > - killsiwtch is turend off > > Here rfkill core routines are called. Rfkill wants to clear STATUS_RF_KILL_SW > but it can not as state is RFKILL_STATE_HARD_BLOCKED. > > > > - driver clear STATUS_RF_KILL_HW > > > > at this point the driver should clear STATE_RF_KILL_HW and then call > > iwl_rfkill_set_hw_state(). From what I can tell, in > > iwl_rfkill_set_hw_state() the test for iwl_is_rfkill_sw() will cause the > > driver to call rfkill_force_state for RFKILL_STATE_SOFT_BLOCKED > > > > So, from what I understand after the above the status will be > > > > rfkill == RFKILL_STATE_SOFT_BLOCKED, and driver == STATE_RF_KILL_SW > > Thats right. But rfkill core no longer wants to manipulate state via > ->toggle_radio() and radio stays disabled. > > > > - rfkill core is unable to clear STATUS_RF_KILL_SW in driver > > > > I do not understand why this is a problem here. Could you please > > highlight what I am missing? > > In my description I miss the most important part, sorry. Race is when the > switches are performed in that order: > > Radio enabled > - rfkill SW on > - driver HW on > Radio disabled - ok > - rfkill SW off <- problem not clearing STATUS_RF_KILL_SW > - driver HW off > Radio disabled - wrong > > Everything is fine when actions are in that order: > > Radio enabled > - rfkill SW on > - driver HW on > Radio disabled - ok > - driver HW off > - rfkill SW off > Radio enabled - ok Thanks for the explanation. > > > > > > > Additionally call to rfkill_epo() when STATUS_RF_KILL_HW in driver is set > > > cause move to the same situation. > > > > > > In 2.6.31 this problem is fixed due to _total_ rewrite of rfkill subsystem. > > > This is a quite small fix for 2.6.30.x in iwl3945 driver. We disable > > > STATUS_RF_KILL_SW bit regardless of HW bit state. Also report to rfkill > > > subsystem SW switch bit before HW switch bit to move rfkill subsystem > > > to SOFT_BLOCK rather than HARD_BLOCK. > > > > > > Signed-off-by: Stanislaw Gruszka > > > --- > > > I'm not sure if this is good candidate for stable as this is not backport > > > of upstream commit. Also I did not test this patch with other iwlwifi devices, > > > only with iwl3945. > > > > > > drivers/net/wireless/iwlwifi/iwl-rfkill.c | 24 ++++++++++++++---------- > > > 1 files changed, 14 insertions(+), 10 deletions(-) > > > > > > diff --git a/drivers/net/wireless/iwlwifi/iwl-rfkill.c b/drivers/net/wireless/iwlwifi/iwl-rfkill.c > > > index 2ad9faf..d6b6098 100644 > > > --- a/drivers/net/wireless/iwlwifi/iwl-rfkill.c > > > +++ b/drivers/net/wireless/iwlwifi/iwl-rfkill.c > > > @@ -54,21 +54,28 @@ static int iwl_rfkill_soft_rf_kill(void *data, enum rfkill_state state) > > > case RFKILL_STATE_UNBLOCKED: > > > if (iwl_is_rfkill_hw(priv)) { > > > err = -EBUSY; > > > - goto out_unlock; > > > + /* pass error to rfkill core to make it state HARD > > > + * BLOCKED and disable software kill switch */ > > > } > > > iwl_radio_kill_sw_enable_radio(priv); > > > break; > > > case RFKILL_STATE_SOFT_BLOCKED: > > > iwl_radio_kill_sw_disable_radio(priv); > > > + /* rfkill->mutex lock is taken */ > > > + if (priv->rfkill->state == RFKILL_STATE_HARD_BLOCKED) { > > > + /* force rfkill core state to be SOFT BLOCKED, > > > + * otherwise core will be unable to disable software > > > + * kill switch */ > > > + priv->rfkill->state = RFKILL_STATE_SOFT_BLOCKED; > > > + } > > > > I understand that you are directly changing the rfkill internals because > > the mutex is taken ... but this really does not seem right to directly > > modify the rfkill state in this way. > > Agree this is dirty hack, but I did not find a better way. Eventually, > if we add call to rfkill_uevent(), this would behave the same > as rfkill_force_state() . Sorry, but I really do not understand why this code is needed. From what you say rfkill can be in one of three states: RFKILL_STATE_UNBLOCKED, RFKILL_STATE_SOFT_BLOCKED, or RFKILL_STATE_HARD_BLOCKED. From what I understand the above code is called when there is an rfkill state change and the new state is provided. So, only _one_ of the three states will be provided as parameter. This state is then tested - so in the case that you modified here the state has already been tested to be RFKILL_STATE_SOFT_BLOCKED. How is it thus possible that it can be RFKILL_STATE_HARD_BLOCKED also? Reinette