netdev - Re: [PATCH RFC 1/2] brcmfmac: remove interface before notifying listener

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Date:	Sat, 18 Jun 2016 23:58:50 +0200
From:	Rafał Miłecki <zajec5@...il.com>
To:	Arend van Spriel <arend.vanspriel@...adcom.com>
Cc:	Kalle Valo <kvalo@...eaurora.org>,
	Franky Lin <franky.lin@...adcom.com>,
	Hante Meuleman <hante.meuleman@...adcom.com>,
	Pieter-Paul Giesberts <pieter-paul.giesberts@...adcom.com>,
	"Franky (Zhenhui) Lin" <frankyl@...adcom.com>,
	"open list:BROADCOM BRCM80211 IEEE802.11n WIRELESS DRIVER" 
	<linux-wireless@...r.kernel.org>,
	"open list:BROADCOM BRCM80211 IEEE802.11n WIRELESS DRIVER" 
	<brcm80211-dev-list.pdl@...adcom.com>,
	"open list:NETWORKING DRIVERS" <netdev@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 1/2] brcmfmac: remove interface before notifying listener

On 18 June 2016 at 21:26, Arend van Spriel <arend.vanspriel@...adcom.com> wrote:
> On 18-06-16 20:18, Rafał Miłecki wrote:
>> So far when receiving event about in-firmware-interface removal we were
>> notifying our listener and afterwards we were removing Linux interface.
>>
>
> [snip]
>
>>
>> diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/fweh.c b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/fweh.c
>> index 9da7a4c..5fd1886 100644
>> --- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/fweh.c
>> +++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/fweh.c
>> @@ -18,6 +18,7 @@
>>  #include "brcmu_wifi.h"
>>  #include "brcmu_utils.h"
>>
>> +#include "cfg80211.h"
>>  #include "core.h"
>>  #include "debug.h"
>>  #include "tracepoint.h"
>> @@ -180,10 +181,16 @@ static void brcmf_fweh_handle_if_event(struct brcmf_pub *drvr,
>>       if (ifp && ifevent->action == BRCMF_E_IF_CHANGE)
>>               brcmf_fws_reset_interface(ifp);
>>
>> -     err = brcmf_fweh_call_event_handler(ifp, emsg->event_code, emsg, data);
>
> The reason for doing this first is because we are passing the ifp, which
> is netdev_priv(ifp->ndev). In brcmf_remove_interface() we only
> unregister the netdev, which will end up (after scheduling) in
> brcmf_free_netdev() thus freeing the ifp. By moving the event handler
> function ifp may be stale already.

Good catch. What about making brcmf_fweh_call_event_handler work
without ifp? Would that be OK then?


>> +     if (ifp && ifevent->action == BRCMF_E_IF_DEL) {
>> +             bool rtnl_locked = brcmf_cfg80211_vif_event_armed(drvr->config);
>> +
>> +             brcmf_remove_interface(ifp, rtnl_locked);
>
> I guess rtnl_locked here means "rtnl_is_locked() by brcmfmac". It
> actually does not matter who is holding the rtnl_lock. At least when it
> is brcmfmac it is still a different task, ie. hostapd, iw, etc. Also
> when brcmf_cfg80211_vif_event_armed() return false there may still be
> some task holding the rtnl_lock.

It does matter who holds the lock.

If it's e.g. some other driver (ath, intel, ralink, whatever) we still
should call unregister_netdevice. It'll just wait until rtnl lock gets
released.

If it's brcmfmac holding the lock, we can't expect it to be released
as brcmfmac waits for completion event.

-- 
Rafał