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Message-ID: <PH7PR11MB58196FC83A5134CAFEDC27CE998AA@PH7PR11MB5819.namprd11.prod.outlook.com>
Date: Fri, 8 Dec 2023 11:53:12 +0000
From: "Sokolowski, Jan" <jan.sokolowski@...el.com>
To: "Fijalkowski, Maciej" <maciej.fijalkowski@...el.com>,
"bpf@...r.kernel.org" <bpf@...r.kernel.org>, "ast@...nel.org"
<ast@...nel.org>, "daniel@...earbox.net" <daniel@...earbox.net>,
"andrii@...nel.org" <andrii@...nel.org>
CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "Karlsson, Magnus"
<magnus.karlsson@...el.com>, "bjorn@...nel.org" <bjorn@...nel.org>,
"Fijalkowski, Maciej" <maciej.fijalkowski@...el.com>, "Chaudron, Eelco"
<echaudro@...hat.com>, "lorenzo@...nel.org" <lorenzo@...nel.org>
Subject: RE: [PATCH bpf 3/3] ice: work on pre-XDP prog frag count
>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")
>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 9e97ea863068..6878448ba112 100644
>--- a/drivers/net/ethernet/intel/ice/ice_txrx.c
>+++ b/drivers/net/ethernet/intel/ice/ice_txrx.c
>@@ -600,9 +600,7 @@ 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);
> }
>
> /**
>@@ -890,14 +888,17 @@ 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);
>@@ -1249,6 +1250,7 @@ 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)))
>@@ -1264,10 +1266,12 @@ 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 daf7b9dbb143..b28b9826bbcd 100644
>--- a/drivers/net/ethernet/intel/ice/ice_txrx.h
>+++ b/drivers/net/ethernet/intel/ice/ice_txrx.h
>@@ -333,6 +333,7 @@ struct ice_rx_ring {
> struct ice_channel *ch;
> struct ice_tx_ring *xdp_ring;
> struct xsk_buff_pool *xsk_pool;
>+ u32 nr_frags;
> dma_addr_t dma; /* physical address of ring */
> u64 cached_phctime;
> u16 rx_buf_len;
>diff --git a/drivers/net/ethernet/intel/ice/ice_txrx_lib.h b/drivers/net/ethernet/intel/ice/ice_txrx_lib.h
>index 115969ecdf7b..b0e56675f98b 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--;
>+ }
> }
> }
>
>--
>2.34.1
>
Reviewed-by: Jan Sokolowski <jan.sokolowski@...el.com>
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