netdev - Re: [PATCH] net: suppress warnings on dev_alloc

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Date:	Wed, 18 May 2016 10:57:21 -0700
From:	Alexander Duyck <alexander.duyck@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Neil Horman <nhorman@...driver.com>,
	Netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] net: suppress warnings on dev_alloc_skb

On Wed, May 18, 2016 at 9:01 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Wed, 2016-05-18 at 11:25 -0400, Neil Horman wrote:
>> Noticed an allocation failure in a network driver the other day on a 32 bit
>> system:
>>
>> DMA-API: debugging out of memory - disabling
>> bnx2fc: adapter_lookup: hba NULL
>> lldpad: page allocation failure. order:0, mode:0x4120
>> Pid: 4556, comm: lldpad Not tainted 2.6.32-639.el6.i686.debug #1
>> Call Trace:
>>  [<c08a4086>] ? printk+0x19/0x23
>>  [<c05166a4>] ? __alloc_pages_nodemask+0x664/0x830
>>  [<c0649d02>] ? free_object+0x82/0xa0
>>  [<fb4e2c9b>] ? ixgbe_alloc_rx_buffers+0x10b/0x1d0 [ixgbe]
>>  [<fb4e2fff>] ? ixgbe_configure_rx_ring+0x29f/0x420 [ixgbe]
>>  [<fb4e228c>] ? ixgbe_configure_tx_ring+0x15c/0x220 [ixgbe]
>>  [<fb4e3709>] ? ixgbe_configure+0x589/0xc00 [ixgbe]
>>  [<fb4e7be7>] ? ixgbe_open+0xa7/0x5c0 [ixgbe]
>>  [<fb503ce6>] ? ixgbe_init_interrupt_scheme+0x5b6/0x970 [ixgbe]
>>  [<fb4e8e54>] ? ixgbe_setup_tc+0x1a4/0x260 [ixgbe]
>>  [<fb505a9f>] ? ixgbe_dcbnl_set_state+0x7f/0x90 [ixgbe]
>>  [<c088d80d>] ? dcb_doit+0x10ed/0x16d0
>> ...
>
>
> Well, maybe this call site (via ixgbe_configure_rx_ring()) should be
> using GFP_KERNEL instead of GFP_ATOMIC.

The problem is the ixgbe driver is using the same function for
allocating memory in the softirq and in the init.  As such it has to
default to GFP_ATOMIC so that it doesn't screw up the NAPI allocation
case.

> Otherwise, if you are unlucky, not a single page would be allocated and
> RX ring buffer would be empty.
>
> So the 'fix' could be limited to GFP_ATOMIC callers ?
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index c413c588a24f854be9e4df78d8a6872b6b1ff9f3..61b923f1520845145a5470d752b278d283cbb348 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -2467,7 +2467,7 @@ static inline struct page *__dev_alloc_pages(gfp_t gfp_mask,
>
>  static inline struct page *dev_alloc_pages(unsigned int order)
>  {
> -       return __dev_alloc_pages(GFP_ATOMIC, order);
> +       return __dev_alloc_pages(GFP_ATOMIC | __GFP_NOWARN, order);
>  }
>
>  /**
> @@ -2485,7 +2485,7 @@ static inline struct page *__dev_alloc_page(gfp_t gfp_mask)
>
>  static inline struct page *dev_alloc_page(void)
>  {
> -       return __dev_alloc_page(GFP_ATOMIC);
> +       return dev_alloc_pages(0);
>  }
>
>  /**
>
>

I agree.  This is likely a much better way to go.

- Alex