From: Jesper Dangaard Brouer <jbrouer@xxxxxxxxxx> Date: Wed, 15 Mar 2023 15:55:44 +0100 > > On 13/03/2023 22.55, Alexander Lobakin wrote: >> __xdp_build_skb_from_frame() state(d): >> >> /* Until page_pool get SKB return path, release DMA here */ >> >> Page Pool got skb pages recycling in April 2021, but missed this >> function. >> >> xdp_release_frame() is relevant only for Page Pool backed frames and it >> detaches the page from the corresponding page_pool in order to make it >> freeable via page_frag_free(). It can instead just mark the output skb >> as eligible for recycling if the frame is backed by a pp. No change for >> other memory model types (the same condition check as before). >> cpumap redirect and veth on Page Pool drivers now become zero-alloc (or >> almost). >> >> Signed-off-by: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx> >> --- >> net/core/xdp.c | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/net/core/xdp.c b/net/core/xdp.c >> index 8c92fc553317..a2237cfca8e9 100644 >> --- a/net/core/xdp.c >> +++ b/net/core/xdp.c >> @@ -658,8 +658,8 @@ struct sk_buff *__xdp_build_skb_from_frame(struct >> xdp_frame *xdpf, >> * - RX ring dev queue index (skb_record_rx_queue) >> */ >> - /* Until page_pool get SKB return path, release DMA here */ >> - xdp_release_frame(xdpf); >> + if (xdpf->mem.type == MEM_TYPE_PAGE_POOL) >> + skb_mark_for_recycle(skb); > > I hope this is safe ;-) ... Meaning hopefully drivers does the correct > thing when XDP_REDIRECT'ing page_pool pages. Safe when it's done by the schoolbook. For now I'm observing only one syzbot issue with test_run due to that it assumes yet another bunch o'things I wouldn't rely on :D (separate subthread) > > Looking for drivers doing weird refcnt tricks and XDP_REDIRECT'ing, I > noticed the driver aquantia/atlantic (in aq_get_rxpages_xdp), but I now > see this is not using page_pool, so it should be affected by this (but I > worry if atlantic driver have a potential race condition for its refcnt > scheme). If we encounter some driver using Page Pool, but mangling refcounts on redirect, we'll fix it ;) > >> /* Allow SKB to reuse area used by xdp_frame */ >> xdp_scrub_frame(xdpf); > Thanks, Olek
