Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751977AbdHPKYt (ORCPT ); Wed, 16 Aug 2017 06:24:49 -0400 Received: from mail-io0-f195.google.com ([209.85.223.195]:38736 "EHLO mail-io0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751841AbdHPKYr (ORCPT ); Wed, 16 Aug 2017 06:24:47 -0400 Message-ID: <1502879084.4936.95.camel@edumazet-glaptop3.roam.corp.google.com> Subject: Re: [PATCH net-next V2 1/3] tap: use build_skb() for small packet From: Eric Dumazet To: Jason Wang Cc: davem@davemloft.net, mst@redhat.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kubakici@wp.pl Date: Wed, 16 Aug 2017 03:24:44 -0700 In-Reply-To: <2ae570ab-01da-2ea2-0549-3e310158b817@redhat.com> References: <1502451678-17358-1-git-send-email-jasowang@redhat.com> <1502451678-17358-2-git-send-email-jasowang@redhat.com> <1502855120.4936.89.camel@edumazet-glaptop3.roam.corp.google.com> <2ae570ab-01da-2ea2-0549-3e310158b817@redhat.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.10.4-0ubuntu2 Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1720 Lines: 58 On Wed, 2017-08-16 at 11:55 +0800, Jason Wang wrote: > > On 2017年08月16日 11:45, Eric Dumazet wrote: > > > > You do realize that tun_build_skb() is not thread safe ? > > Ok, I think the issue if skb_page_frag_refill(), need a spinlock > probably. Will prepare a patch. But since tun is used from process context, why don't you use the per-thread generator (no lock involved) tcp_sendmsg() uses this for GFP_KERNEL allocations. Untested patch : diff --git a/drivers/net/tun.c b/drivers/net/tun.c index 5892284eb8d05b0678d820bad3d0d2c61a879aeb..c38cd840cc0b7fecf182b23976e36f709cacca1f 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -175,7 +175,6 @@ struct tun_file { struct list_head next; struct tun_struct *detached; struct skb_array tx_array; - struct page_frag alloc_frag; }; struct tun_flow_entry { @@ -578,8 +577,6 @@ static void __tun_detach(struct tun_file *tfile, bool clean) } if (tun) skb_array_cleanup(&tfile->tx_array); - if (tfile->alloc_frag.page) - put_page(tfile->alloc_frag.page); sock_put(&tfile->sk); } } @@ -1272,7 +1269,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun, struct virtio_net_hdr *hdr, int len, int *generic_xdp) { - struct page_frag *alloc_frag = &tfile->alloc_frag; + struct page_frag *alloc_frag = ¤t->task_frag; struct sk_buff *skb; struct bpf_prog *xdp_prog; int buflen = SKB_DATA_ALIGN(len + TUN_RX_PAD) + @@ -2580,8 +2577,6 @@ static int tun_chr_open(struct inode *inode, struct file * file) tfile->sk.sk_write_space = tun_sock_write_space; tfile->sk.sk_sndbuf = INT_MAX; - tfile->alloc_frag.page = NULL; - file->private_data = tfile; INIT_LIST_HEAD(&tfile->next);