linux-kernel - Re: [PATCH 3/5] staging: rtl8188eu: use is_multicast_ether_addr in rtw

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Message-ID: <cf3e257702a93e4fcfab666e42e49f363eb447f7.camel@perches.com>
Date:   Thu, 09 Aug 2018 10:51:49 -0700
From:   Joe Perches <joe@...ches.com>
To:     Michael Straube <straube.linux@...il.com>,
        gregkh@...uxfoundation.org
Cc:     devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        Alexander Duyck <alexander.h.duyck@...hat.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 3/5] staging: rtl8188eu: use is_multicast_ether_addr in
 rtw_xmit.c

On Thu, 2018-08-09 at 19:42 +0200, Michael Straube wrote:
> On 8/9/18 7:13 PM, Joe Perches wrote:
> > On Thu, 2018-08-09 at 19:01 +0200, Michael Straube wrote:
> > > Use is_multicast_ether_addr instead of custom IS_MCAST in
> > > core/rtw_xmit.c.
> > 
> > Have you verified that all accesses are __aligned(2) ?
> > 
> > If so, please state that in the patch description.
> > 
> > > diff --git a/drivers/staging/rtl8188eu/core/rtw_xmit.c b/drivers/staging/rtl8188eu/core/rtw_xmit.c
> > 
> > []
> > > @@ -460,10 +460,10 @@ static s32 update_attrib(struct adapter *padapter, struct sk_buff *pkt, struct p
> > >   	if ((pattrib->ether_type == ETH_P_ARP) || (pattrib->ether_type == ETH_P_PAE) || (pattrib->dhcp_pkt == 1))
> > >   		rtw_lps_ctrl_wk_cmd(padapter, LPS_CTRL_SPECIAL_PACKET, 1);
> > >   
> > > -	bmcast = IS_MCAST(pattrib->ra);
> > > +	mcast = is_multicast_ether_addr(pattrib->ra);
> > 
> > i.e.:  is pattrib->ra __aligned(2) ?
> > 
> > etc...
> > 
> 
> Hi Joe,
> 
> I looked at the function comment for is_multicast_ether_addr in etherdevice.h.
> There is not mentioned that __aligned(2) is required. If it is, I will check.
> 
> So, is it required although it's not mentioned for is_multicast_ether_addr?

Well, it wasn't required initially, but

commit d54385ce68cd18ab002b46f61246ad197cec92de
Author: Alexander Duyck <alexander.h.duyck@...hat.com>
Date:   Thu Apr 30 14:53:54 2015 -0700

    etherdev: Process is_multicast_ether_addr at same size as other operations
    
    This change makes it so that we process the address in
    is_multicast_ether_addr at the same size as the other calls.  This allows
    us to avoid duplicate reads when used with other calls such as
    is_zero_ether_addr or eth_addr_copy.  In addition I have added a 64 bit
    version of the function so in eth_type_trans we can process the destination
    address as a 64 bit value throughout.
    
    Signed-off-by: Alexander Duyck <alexander.h.duyck@...hat.com>
    Signed-off-by: David S. Miller <davem@...emloft.net>

changed it without adding a note in the kernel-doc.

So this is likely appropriate to avoid unaligned access traps:
---
 include/linux/etherdevice.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/etherdevice.h b/include/linux/etherdevice.h
index 572e11bb8696..0f7086b4836a 100644
--- a/include/linux/etherdevice.h
+++ b/include/linux/etherdevice.h
@@ -115,6 +115,8 @@ static inline bool is_zero_ether_addr(const u8 *addr)
  *
  * Return true if the address is a multicast address.
  * By definition the broadcast address is also a multicast address.
+ *
+ * Please note: addr must be aligned to u16.
  */
 static inline bool is_multicast_ether_addr(const u8 *addr)
 {