Re: [PATCH RFC net-next 1/4] net: skbuff: don't include <net/page_pool.h> to <linux/skbuff.h>

[Alexander H Duyck]

On Thu, 2023-06-29 at 17:23 +0200, Alexander Lobakin wrote:
> Currently, touching <net/page_pool.h> triggers a rebuild of more than
> a half of the kernel. That's because it's included in <linux/skbuff.h>.
> And each new include to page_pool.h adds more [useless] data for the
> toolchain to process per each source file from that pile.
> 
> In commit 6a5bcd84e886 ("page_pool: Allow drivers to hint on SKB
> recycling"), Matteo included it to be able to call a couple functions
> defined there. Then, in commit 57f05bc2ab24 ("page_pool: keep pp info
> as long as page pool owns the page") one of the calls was removed, so
> only one left. It's the call to page_pool_return_skb_page() in
> napi_frag_unref(). The function is external and doesn't have any
> dependencies. Having include of very niche page_pool.h only for that
> looks like an overkill.
> As Alex noticed, the only thing that holds this function in page_pool.c
> is %PP_SIGNATURE. By moving the check for magic a couple functions up,
> the whole page_pool_return_skb_page() can be moved to skbuff.c.
> The arguments for moving the check are the following:
> 
> 1) It checks for a corner case that shouldn't ever happen when the code
>    is sane. And execution speed doesn't matter on exception path, thus
>    doing more calls before bailing out doesn't make any weather.
> 2) There are 2 users of the internal __page_pool_put_page(), where this
>    check is moved: page_pool_put_defragged_page() and
>    page_pool_put_page_bulk(). Both are exported and can be called from
>    the drivers, but previously only the skb recycling path of the former
>    was protected with the magic check. So this also makes the code a bit
>    more reliable.
> 
> After the check is moved, teleport page_pool_return_skb_page() to
> skbuff.c, just next to the main consumer, skb_pp_recycle(). It's used
> also in napi_frag_unref() -> {__,}skb_frag_unref(), so no `static`
> unfortunately. Maybe next time.
> Now, after a few include fixes in the drivers, touching page_pool.h
> only triggers rebuilding of the drivers using it and a couple core
> networking files.
> 
> Suggested-by: Jakub Kicinski <kuba@xxxxxxxxxx> # make skbuff.h less heavy
> Suggested-by: Alexander Duyck <alexanderduyck@xxxxxx> # move to skbuff.c
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx>
> ---
>  drivers/net/ethernet/engleder/tsnep_main.c    |  1 +
>  drivers/net/ethernet/freescale/fec_main.c     |  1 +
>  .../marvell/octeontx2/nic/otx2_common.c       |  1 +
>  .../ethernet/marvell/octeontx2/nic/otx2_pf.c  |  1 +
>  .../ethernet/mellanox/mlx5/core/en/params.c   |  1 +
>  .../net/ethernet/mellanox/mlx5/core/en/xdp.c  |  1 +
>  drivers/net/wireless/mediatek/mt76/mt76.h     |  1 +
>  include/linux/skbuff.h                        |  3 +-
>  include/net/page_pool.h                       |  2 -
>  net/core/page_pool.c                          | 52 +++++--------------
>  net/core/skbuff.c                             | 28 ++++++++++
>  11 files changed, 50 insertions(+), 42 deletions(-)
> 
> diff --git a/drivers/net/ethernet/engleder/tsnep_main.c b/drivers/net/ethernet/engleder/tsnep_main.c
> index 84751bb303a6..6222aaa5157f 100644
> --- a/drivers/net/ethernet/engleder/tsnep_main.c
> +++ b/drivers/net/ethernet/engleder/tsnep_main.c
> @@ -28,6 +28,7 @@
>  #include <linux/iopoll.h>
>  #include <linux/bpf.h>
>  #include <linux/bpf_trace.h>
> +#include <net/page_pool.h>
>  #include <net/xdp_sock_drv.h>
>  
>  #define TSNEP_RX_OFFSET (max(NET_SKB_PAD, XDP_PACKET_HEADROOM) + NET_IP_ALIGN)
> diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
> index 8fbe47703d47..99b3b4f79603 100644
> --- a/drivers/net/ethernet/freescale/fec_main.c
> +++ b/drivers/net/ethernet/freescale/fec_main.c
> @@ -38,6 +38,7 @@
>  #include <linux/in.h>
>  #include <linux/ip.h>
>  #include <net/ip.h>
> +#include <net/page_pool.h>
>  #include <net/selftests.h>
>  #include <net/tso.h>
>  #include <linux/tcp.h>
> diff --git a/drivers/net/ethernet/marvell/octeontx2/nic/otx2_common.c b/drivers/net/ethernet/marvell/octeontx2/nic/otx2_common.c
> index a5d03583bf79..d17a0ebc9036 100644
> --- a/drivers/net/ethernet/marvell/octeontx2/nic/otx2_common.c
> +++ b/drivers/net/ethernet/marvell/octeontx2/nic/otx2_common.c
> @@ -7,6 +7,7 @@
>  
>  #include <linux/interrupt.h>
>  #include <linux/pci.h>
> +#include <net/page_pool.h>
>  #include <net/tso.h>
>  #include <linux/bitfield.h>
>  
> diff --git a/drivers/net/ethernet/marvell/octeontx2/nic/otx2_pf.c b/drivers/net/ethernet/marvell/octeontx2/nic/otx2_pf.c
> index fe8ea4e531b7..7eca434a0550 100644
> --- a/drivers/net/ethernet/marvell/octeontx2/nic/otx2_pf.c
> +++ b/drivers/net/ethernet/marvell/octeontx2/nic/otx2_pf.c
> @@ -16,6 +16,7 @@
>  #include <linux/bpf.h>
>  #include <linux/bpf_trace.h>
>  #include <linux/bitfield.h>
> +#include <net/page_pool.h>
>  
>  #include "otx2_reg.h"
>  #include "otx2_common.h"
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/params.c b/drivers/net/ethernet/mellanox/mlx5/core/en/params.c
> index 5ce28ff7685f..0f152f14165b 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en/params.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en/params.c
> @@ -6,6 +6,7 @@
>  #include "en/port.h"
>  #include "en_accel/en_accel.h"
>  #include "en_accel/ipsec.h"
> +#include <net/page_pool.h>
>  #include <net/xdp_sock_drv.h>
>  
>  static u8 mlx5e_mpwrq_min_page_shift(struct mlx5_core_dev *mdev)
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
> index f0e6095809fa..1bd91bc09eb8 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
> @@ -35,6 +35,7 @@
>  #include "en/xdp.h"
>  #include "en/params.h"
>  #include <linux/bitfield.h>
> +#include <net/page_pool.h>
>  
>  int mlx5e_xdp_max_mtu(struct mlx5e_params *params, struct mlx5e_xsk_param *xsk)
>  {
> diff --git a/drivers/net/wireless/mediatek/mt76/mt76.h b/drivers/net/wireless/mediatek/mt76/mt76.h
> index 6b07b8fafec2..95c16f11d156 100644
> --- a/drivers/net/wireless/mediatek/mt76/mt76.h
> +++ b/drivers/net/wireless/mediatek/mt76/mt76.h
> @@ -15,6 +15,7 @@
>  #include <linux/average.h>
>  #include <linux/soc/mediatek/mtk_wed.h>
>  #include <net/mac80211.h>
> +#include <net/page_pool.h>
>  #include "util.h"
>  #include "testmode.h"
>  
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 91ed66952580..f76d172ed262 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -32,7 +32,6 @@
>  #include <linux/if_packet.h>
>  #include <linux/llist.h>
>  #include <net/flow.h>
> -#include <net/page_pool.h>
>  #if IS_ENABLED(CONFIG_NF_CONNTRACK)
>  #include <linux/netfilter/nf_conntrack_common.h>
>  #endif
> @@ -3423,6 +3422,8 @@ static inline void skb_frag_ref(struct sk_buff *skb, int f)
>  	__skb_frag_ref(&skb_shinfo(skb)->frags[f]);
>  }
>  
> +bool page_pool_return_skb_page(struct page *page, bool napi_safe);
> +
>  static inline void
>  napi_frag_unref(skb_frag_t *frag, bool recycle, bool napi_safe)
>  {
> diff --git a/include/net/page_pool.h b/include/net/page_pool.h
> index 2b7db9992fc0..829dc1f8ba6b 100644
> --- a/include/net/page_pool.h
> +++ b/include/net/page_pool.h
> @@ -307,8 +307,6 @@ inline enum dma_data_direction page_pool_get_dma_dir(struct page_pool *pool)
>  	return pool->p.dma_dir;
>  }
>  
> -bool page_pool_return_skb_page(struct page *page, bool napi_safe);
> -
>  struct page_pool *page_pool_create(const struct page_pool_params *params);
>  
>  struct xdp_mem_info;
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index 985ccaffc06a..dff0b4fa2316 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -582,6 +582,19 @@ static __always_inline struct page *
>  __page_pool_put_page(struct page_pool *pool, struct page *page,
>  		     unsigned int dma_sync_size, bool allow_direct)
>  {
> +	/* Avoid recycling non-PP pages, give them back to the page allocator.
> +	 * page->pp_magic is OR'ed with PP_SIGNATURE after the allocation
> +	 * in order to preserve any existing bits, such as bit 0 for the
> +	 * head page of compound page and bit 1 for pfmemalloc page, so
> +	 * mask those bits for freeing side when doing below checking,
> +	 * and page_is_pfmemalloc() is checked in __page_pool_put_page()
> +	 * to avoid recycling the pfmemalloc page.
> +	 */
> +	if (unlikely((page->pp_magic & ~0x3UL) != PP_SIGNATURE)) {
> +		put_page(page);
> +		return NULL;
> +	}
> +

Rather than moving this block of code down into here. You may just want
to look at creating an inline function that would act as a accessor for
retrieving the page pool for pages with the signature, and for those
without just returning NULL.

>  	/* This allocator is optimized for the XDP mode that uses
>  	 * one-frame-per-page, but have fallbacks that act like the
>  	 * regular page allocator APIs.
> @@ -913,42 +926,3 @@ void page_pool_update_nid(struct page_pool *pool, int new_nid)
>  	}
>  }
>  EXPORT_SYMBOL(page_pool_update_nid);
> -
> -bool page_pool_return_skb_page(struct page *page, bool napi_safe)
> -{
> -	struct napi_struct *napi;
> -	struct page_pool *pp;
> -	bool allow_direct;
> -
> -	page = compound_head(page);
> -
> -	/* page->pp_magic is OR'ed with PP_SIGNATURE after the allocation
> -	 * in order to preserve any existing bits, such as bit 0 for the
> -	 * head page of compound page and bit 1 for pfmemalloc page, so
> -	 * mask those bits for freeing side when doing below checking,
> -	 * and page_is_pfmemalloc() is checked in __page_pool_put_page()
> -	 * to avoid recycling the pfmemalloc page.
> -	 */
> -	if (unlikely((page->pp_magic & ~0x3UL) != PP_SIGNATURE))
> -		return false;
> -
> -	pp = page->pp;
> -
> -	/* Allow direct recycle if we have reasons to believe that we are
> -	 * in the same context as the consumer would run, so there's
> -	 * no possible race.
> -	 */
> -	napi = READ_ONCE(pp->p.napi);
> -	allow_direct = napi_safe && napi &&
> -		READ_ONCE(napi->list_owner) == smp_processor_id();
> -
> -	/* Driver set this to memory recycling info. Reset it on recycle.
> -	 * This will *not* work for NIC using a split-page memory model.
> -	 * The page will be returned to the pool here regardless of the
> -	 * 'flipped' fragment being in use or not.
> -	 */
> -	page_pool_put_full_page(pp, page, allow_direct);
> -
> -	return true;
> -}
> -EXPORT_SYMBOL(page_pool_return_skb_page);
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 7edabf17988a..4b7d00d5b5d7 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -879,6 +879,34 @@ static void skb_clone_fraglist(struct sk_buff *skb)
>  		skb_get(list);
>  }
>  
> +bool page_pool_return_skb_page(struct page *page, bool napi_safe)
> +{
> +	struct napi_struct *napi;
> +	struct page_pool *pp;
> +	bool allow_direct;
> +
> +	page = compound_head(page);
> +	pp = page->pp;

So this is just assuming that any page we pass thru is a page pool
page. The problem is there may be some other pointer stored here that
could cause issues.

I would suggest creating an accessor as mentioned above to verify it is
a page pool page before you access page->pp.

> +
> +	/* Allow direct recycle if we have reasons to believe that we are
> +	 * in the same context as the consumer would run, so there's
> +	 * no possible race.
> +	 */
> +	napi = READ_ONCE(pp->p.napi);
> +	allow_direct = napi_safe && napi &&
> +		READ_ONCE(napi->list_owner) == smp_processor_id();
> +
> +	/* Driver set this to memory recycling info. Reset it on recycle.
> +	 * This will *not* work for NIC using a split-page memory model.
> +	 * The page will be returned to the pool here regardless of the
> +	 * 'flipped' fragment being in use or not.
> +	 */
> +	page_pool_put_full_page(pp, page, allow_direct);
> +
> +	return true;
> +}
> +EXPORT_SYMBOL(page_pool_return_skb_page);
> +
>  static bool skb_pp_recycle(struct sk_buff *skb, void *data, bool napi_safe)
>  {
>  	if (!IS_ENABLED(CONFIG_PAGE_POOL) || !skb->pp_recycle)