netdev - Re: [E1000-devel] [next:akpm 16/587] drivers/net/ethernet/intel/igb/igb_main.c:6231:2: error: call to '__compiletime_assert_6235' declared with attribute error: BUILD_BUG_ON failed: SKB_WITH_OVERHEAD(IGB_RX_BUFSZ) < (NET_SKB_PAD + NET_IP_ALIGN + IGB_TS_HDR

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Message-ID: <51251303.9030803@intel.com>
Date:	Wed, 20 Feb 2013 10:16:35 -0800
From:	Alexander Duyck <alexander.h.duyck@...el.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	"Allan, Bruce W" <bruce.w.allan@...el.com>,
	"e1000-devel@...ts.sourceforge.net" 
	<e1000-devel@...ts.sourceforge.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
	Daniel Santos <daniel.santos@...ox.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Wu, Fengguang" <fengguang.wu@...el.com>
Subject: Re: [E1000-devel] [next:akpm 16/587] drivers/net/ethernet/intel/igb/igb_main.c:6231:2:
 error: call to '__compiletime_assert_6235' declared with attribute error:
 BUILD_BUG_ON failed: SKB_WITH_OVERHEAD(IGB_RX_BUFSZ) < (NET_SKB_PAD + NET_IP_ALIGN
 + IGB_TS_HDR_LEN + ETH...

On 02/19/2013 05:09 PM, Eric Dumazet wrote:
> On Tue, Feb 19, 2013 at 2:30 PM, Allan, Bruce W <bruce.w.allan@...el.com> wrote:
>>> -----Original Message-----
>>> From: Andrew Morton [mailto:akpm@...ux-foundation.org]
>>> Sent: Tuesday, February 19, 2013 2:27 PM
>>> To: Wu, Fengguang
>>> Cc: Daniel Santos; Kirsher, Jeffrey T; Brandeburg, Jesse; Allan, Bruce W;
>>> netdev@...r.kernel.org
>>> Subject: Re: [next:akpm 16/587]
>>> drivers/net/ethernet/intel/igb/igb_main.c:6231:2: error: call to
>>> '__compiletime_assert_6235' declared with attribute error: BUILD_BUG_ON
>>> failed: SKB_WITH_OVERHEAD(IGB_RX_BUFSZ) < (NET_SKB_PAD +
>>> NET_IP_ALIGN + IGB_TS_HDR_LEN + ETH...
>>>
>>> On Mon, 18 Feb 2013 19:27:22 +0800
>>> kbuild test robot <fengguang.wu@...el.com> wrote:
>>>
>>>> tree:   git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
>>> akpm
>>>> head:   ae9da2a24a80423b8dbda9c5a72674ce6e7861be
>>>> commit: f7d7e38e6df399b2af7f04c177054abdd744a077 [16/587] bug.h,
>>> compiler.h: Introduce compiletime_assert & BUILD_BUG_ON_MSG
>>>> config: make ARCH=s390 allmodconfig
>>>>
>>>> All error/warnings:
>>>>
>>>>    In function 'igb_build_rx_buffer',
>>>>        inlined from 'igb_clean_rx_irq' at
>>> drivers/net/ethernet/intel/igb/igb_main.c:6705:8:
>>>>>> drivers/net/ethernet/intel/igb/igb_main.c:6231:2: error: call to
>>> '__compiletime_assert_6235' declared with attribute error: BUILD_BUG_ON
>>> failed: SKB_WITH_OVERHEAD(IGB_RX_BUFSZ) < (NET_SKB_PAD +
>>> NET_IP_ALIGN + IGB_TS_HDR_LEN + ETH_FRAME_LEN + ETH_FCS_LEN)
>>>> vim +/__compiletime_assert_6235 +6231
>>> drivers/net/ethernet/intel/igb/igb_main.c
>>>>   6225      #endif
>>>>   6226
>>>>   6227              /* If we spanned a buffer we have a huge mess so test for it
>>> */
>>>>   6228              BUG_ON(unlikely(!igb_test_staterr(rx_desc,
>>> E1000_RXD_STAT_EOP)));
>>>>   6229
>>>>   6230              /* Guarantee this function can be used by verifying buffer
>>> sizes */
>>>>> 6231
>>>       BUILD_BUG_ON(SKB_WITH_OVERHEAD(IGB_RX_BUFSZ) <
>>> (NET_SKB_PAD +
>>>>   6232
>>>       NET_IP_ALIGN +
>>>>   6233
>>>       IGB_TS_HDR_LEN +
>>>>   6234
>>>       ETH_FRAME_LEN +
>>> That BUILD_BUG_ON() triggers without Daniel's patches applied as well:
>>>
>>>   CC [M]  drivers/net/ethernet/intel/igb/igb_main.o
>>> drivers/net/ethernet/intel/igb/igb_main.c: In function
>>> 'igb_build_rx_buffer':
>>> drivers/net/ethernet/intel/igb/igb_main.c:6231: error: size of array 'type
>>> name' is negative
>>>
>>> I suspect that driver is busted on s390.  Dunno why.  Here's what cpp emits:
>>>
>>>
>>> s390 allmodconfig:
>>>
>>> bool __cond = !(!(((2048) - (((sizeof(struct skb_shared_info)) + (256 - 1)) &
>>> ~(256 - 1))) < (32 + 2 + 16 + 1514 + 4)));
>>>
>>>
>>> x86_64 allmodconfig:
>>>
>>> bool __cond = !(!(((2048) - (((sizeof(struct skb_shared_info)) + ((1 <<
>>> (6)) - 1)) & ~((1 << (6)) - 1))) < (({ typeof(32) _max1 = (32); typeof((1
>>> << (6))) _max2 = ((1 << (6))); (void) (&_max1 == &_max2); _max1 > _max2 ?
>>> _max1 : _max2; }) + 0 + 16 + 1514 + 4)));
>>>
>>>
>>> I doubt if anyone will be running this driver on s390, but I guess we
>>> should work out why it broke.
>> Adding Intel wired ethernet developers mailing list.
>>
> Oh well, NET_SKB_PAD is too large on s390
>
> I guess we should use 64 bytes max.
>
> #define NET_SKB_PAD  min(64, max(32, L1_CACHE_BYTES))

The problem is the 256 byte alignment for L1_CACHE_BYTES is increasing
the size of the data and shared info significantly pushing us past the
2K limit.

I'll look into this since it likely affects ixgbe as well.

Thanks,

Alex
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