From: David Miller <davem@davemloft.net>
To: tushar.n.dave@oracle.com
Cc: netdev@vger.kernel.org, jeffrey.t.kirsher@intel.com,
jesse.brandeburg@intel.com, shannon.nelson@intel.com,
carolyn.wyborny@intel.com, donald.c.skidmore@intel.com,
bruce.w.allan@intel.com, john.ronciak@intel.com,
mitch.a.williams@intel.com, intel-wired-lan@lists.osuosl.org
Subject: Re: i40e: Kernel unaligned access due to 'struct i40e_dma_mem' being 'packed'
Date: Thu, 28 Jan 2016 01:56:43 -0500 (EST) [thread overview]
Message-ID: <20160128.015643.125847430094859447.davem@davemloft.net> (raw)
In-Reply-To: <56A973D6.4060202@oracle.com>
From: tndave <tushar.n.dave@oracle.com>
Date: Wed, 27 Jan 2016 17:50:14 -0800
> Hi,
>
> i40e driver has 'struct i40e_dma_mem' defined with 'packed' directive
> causing kernel unaligned errors on sparc (when
> 40e_allocate_dma_mem_d()
> is being called)
>
> log_unaligned: 1031 callbacks suppressed
> Kernel unaligned access at TPC[448ae8]
> dma_4v_alloc_coherent+0x188/0x2e0
> Kernel unaligned access at TPC[448ae8]
> dma_4v_alloc_coherent+0x188/0x2e0
> Kernel unaligned access at TPC[448ae8]
> dma_4v_alloc_coherent+0x188/0x2e0
> Kernel unaligned access at TPC[448ae8]
> dma_4v_alloc_coherent+0x188/0x2e0
>
> This can be fixed with get_unaligned/put_unaligned(). However I don't
> see 'struct i40e_dma_mem' is being directly shoved into NIC hardware.
> But instead fields of the struct are being read and used for hardware
> (e.g. dma_addr_t pa). For the test, I remove __packed, and i40e driver
> and HW works fine. (of course kernel unaligned errors are gone too).
> My question is, does 'struct i40e_dma_mem' required to be __packed?
People get overzealoud with __packed.
And even if it doesn't cause unaligned accesses like this, it generates
terrible code (byte at a time accesses to words) on several architectures.
next prev parent reply other threads:[~2016-01-28 6:56 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-28 1:50 i40e: Kernel unaligned access due to 'struct i40e_dma_mem' being 'packed' tndave
2016-01-28 6:56 ` David Miller [this message]
2016-01-29 22:47 ` tndave
2016-02-14 0:22 ` tndave
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