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Message-ID: <f1ce06fd-30da-405e-8082-e35a9a88c5bd@amd.com>
Date: Wed, 24 Jan 2024 18:25:58 -0800
From: Brett Creeley <bcreeley@....com>
To: Maciej Fijalkowski <maciej.fijalkowski@...el.com>, bpf@...r.kernel.org,
ast@...nel.org, daniel@...earbox.net, andrii@...nel.org
Cc: netdev@...r.kernel.org, magnus.karlsson@...el.com, bjorn@...nel.org,
echaudro@...hat.com, lorenzo@...nel.org, martin.lau@...ux.dev,
tirthendu.sarkar@...el.com, john.fastabend@...il.com, horms@...nel.org,
kuba@...nel.org
Subject: Re: [PATCH v6 bpf 04/11] ice: work on pre-XDP prog frag count
On 1/24/2024 11:15 AM, Maciej Fijalkowski wrote:
> Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding.
>
>
> Fix an OOM panic in XDP_DRV mode when a XDP program shrinks a
> multi-buffer packet by 4k bytes and then redirects it to an AF_XDP
> socket.
>
> Since support for handling multi-buffer frames was added to XDP, usage
> of bpf_xdp_adjust_tail() helper within XDP program can free the page
> that given fragment occupies and in turn decrease the fragment count
> within skb_shared_info that is embedded in xdp_buff struct. In current
> ice driver codebase, it can become problematic when page recycling logic
> decides not to reuse the page. In such case, __page_frag_cache_drain()
> is used with ice_rx_buf::pagecnt_bias that was not adjusted after
> refcount of page was changed by XDP prog which in turn does not drain
> the refcount to 0 and page is never freed.
>
> To address this, let us store the count of frags before the XDP program
> was executed on Rx ring struct. This will be used to compare with
> current frag count from skb_shared_info embedded in xdp_buff. A smaller
> value in the latter indicates that XDP prog freed frag(s). Then, for
> given delta decrement pagecnt_bias for XDP_DROP verdict.
>
> While at it, let us also handle the EOP frag within
> ice_set_rx_bufs_act() to make our life easier, so all of the adjustments
> needed to be applied against freed frags are performed in the single
> place.
>
> Fixes: 2fba7dc5157b ("ice: Add support for XDP multi-buffer on Rx side")
> Acked-by: Magnus Karlsson <magnus.karlsson@...el.com>
> Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> ---
> drivers/net/ethernet/intel/ice/ice_txrx.c | 14 ++++++---
> drivers/net/ethernet/intel/ice/ice_txrx.h | 1 +
> drivers/net/ethernet/intel/ice/ice_txrx_lib.h | 31 +++++++++++++------
> 3 files changed, 32 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/ice/ice_txrx.c b/drivers/net/ethernet/intel/ice/ice_txrx.c
> index 74d13cc5a3a7..0c9b4aa8a049 100644
> --- a/drivers/net/ethernet/intel/ice/ice_txrx.c
> +++ b/drivers/net/ethernet/intel/ice/ice_txrx.c
> @@ -603,9 +603,7 @@ ice_run_xdp(struct ice_rx_ring *rx_ring, struct xdp_buff *xdp,
> ret = ICE_XDP_CONSUMED;
> }
> exit:
> - rx_buf->act = ret;
> - if (unlikely(xdp_buff_has_frags(xdp)))
> - ice_set_rx_bufs_act(xdp, rx_ring, ret);
> + ice_set_rx_bufs_act(xdp, rx_ring, ret);
> }
>
> /**
> @@ -893,14 +891,17 @@ ice_add_xdp_frag(struct ice_rx_ring *rx_ring, struct xdp_buff *xdp,
> }
>
> if (unlikely(sinfo->nr_frags == MAX_SKB_FRAGS)) {
> - if (unlikely(xdp_buff_has_frags(xdp)))
> - ice_set_rx_bufs_act(xdp, rx_ring, ICE_XDP_CONSUMED);
> + ice_set_rx_bufs_act(xdp, rx_ring, ICE_XDP_CONSUMED);
> return -ENOMEM;
> }
>
> __skb_fill_page_desc_noacc(sinfo, sinfo->nr_frags++, rx_buf->page,
> rx_buf->page_offset, size);
> sinfo->xdp_frags_size += size;
> + /* remember frag count before XDP prog execution; bpf_xdp_adjust_tail()
> + * can pop off frags but driver has to handle it on its own
> + */
> + rx_ring->nr_frags = sinfo->nr_frags;
>
> if (page_is_pfmemalloc(rx_buf->page))
> xdp_buff_set_frag_pfmemalloc(xdp);
> @@ -1251,6 +1252,7 @@ int ice_clean_rx_irq(struct ice_rx_ring *rx_ring, int budget)
>
> xdp->data = NULL;
> rx_ring->first_desc = ntc;
> + rx_ring->nr_frags = 0;
> continue;
> construct_skb:
> if (likely(ice_ring_uses_build_skb(rx_ring)))
> @@ -1266,10 +1268,12 @@ int ice_clean_rx_irq(struct ice_rx_ring *rx_ring, int budget)
> ICE_XDP_CONSUMED);
> xdp->data = NULL;
> rx_ring->first_desc = ntc;
> + rx_ring->nr_frags = 0;
> break;
> }
> xdp->data = NULL;
> rx_ring->first_desc = ntc;
> + rx_ring->nr_frags = 0;
>
> stat_err_bits = BIT(ICE_RX_FLEX_DESC_STATUS0_RXE_S);
> if (unlikely(ice_test_staterr(rx_desc->wb.status_error0,
> diff --git a/drivers/net/ethernet/intel/ice/ice_txrx.h b/drivers/net/ethernet/intel/ice/ice_txrx.h
> index b3379ff73674..af955b0e5dc5 100644
> --- a/drivers/net/ethernet/intel/ice/ice_txrx.h
> +++ b/drivers/net/ethernet/intel/ice/ice_txrx.h
> @@ -358,6 +358,7 @@ struct ice_rx_ring {
> struct ice_tx_ring *xdp_ring;
> struct ice_rx_ring *next; /* pointer to next ring in q_vector */
> struct xsk_buff_pool *xsk_pool;
> + u32 nr_frags;
> dma_addr_t dma; /* physical address of ring */
> u16 rx_buf_len;
> u8 dcb_tc; /* Traffic class of ring */
> diff --git a/drivers/net/ethernet/intel/ice/ice_txrx_lib.h b/drivers/net/ethernet/intel/ice/ice_txrx_lib.h
> index 762047508619..afcead4baef4 100644
> --- a/drivers/net/ethernet/intel/ice/ice_txrx_lib.h
> +++ b/drivers/net/ethernet/intel/ice/ice_txrx_lib.h
> @@ -12,26 +12,39 @@
> * act: action to store onto Rx buffers related to XDP buffer parts
> *
> * Set action that should be taken before putting Rx buffer from first frag
> - * to one before last. Last one is handled by caller of this function as it
> - * is the EOP frag that is currently being processed. This function is
> - * supposed to be called only when XDP buffer contains frags.
> + * to the last.
> */
> static inline void
> ice_set_rx_bufs_act(struct xdp_buff *xdp, const struct ice_rx_ring *rx_ring,
> const unsigned int act)
> {
> - const struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
> - u32 first = rx_ring->first_desc;
> - u32 nr_frags = sinfo->nr_frags;
> + u32 sinfo_frags = xdp_get_shared_info_from_buff(xdp)->nr_frags;
> + u32 nr_frags = rx_ring->nr_frags + 1;
> + u32 idx = rx_ring->first_desc;
> u32 cnt = rx_ring->count;
> struct ice_rx_buf *buf;
>
> for (int i = 0; i < nr_frags; i++) {
> - buf = &rx_ring->rx_buf[first];
> + buf = &rx_ring->rx_buf[idx];
> buf->act = act;
>
> - if (++first == cnt)
> - first = 0;
> + if (++idx == cnt)
> + idx = 0;
> + }
> +
> + /* adjust pagecnt_bias on frags freed by XDP prog */
> + if (sinfo_frags < rx_ring->nr_frags && act == ICE_XDP_CONSUMED) {
> + u32 delta = rx_ring->nr_frags - sinfo_frags;
> +
> + while (delta) {
> + if (idx == 0)
> + idx = cnt - 1;
> + else
> + idx--;
> + buf = &rx_ring->rx_buf[idx];
> + buf->pagecnt_bias--;
> + delta--;
> + }
Nit, but the function name ice_set_rx_bufs_act() doesn't completely
align with what it's doing anymore due to the additional pagecnt_bias
changes.
> }
> }
>
> --
> 2.34.1
>
>
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