From patchwork Wed Jan 25 12:27:11 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Ian Campbell X-Patchwork-Id: 137744 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id C0260B6F68 for ; Wed, 25 Jan 2012 23:27:27 +1100 (EST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753104Ab2AYM1X (ORCPT ); Wed, 25 Jan 2012 07:27:23 -0500 Received: from smtp02.citrix.com ([66.165.176.63]:61821 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753055Ab2AYM1V (ORCPT ); Wed, 25 Jan 2012 07:27:21 -0500 X-IronPort-AV: E=Sophos;i="4.71,567,1320642000"; d="scan'208";a="179011980" Received: from ftlpmailmx01.citrite.net ([10.13.107.65]) by FTLPIPO02.CITRIX.COM with ESMTP/TLS/RC4-MD5; 25 Jan 2012 07:27:21 -0500 Received: from smtp01.ad.xensource.com (10.219.128.104) by smtprelay.citrix.com (10.13.107.65) with Microsoft SMTP Server id 8.3.213.0; Wed, 25 Jan 2012 07:27:20 -0500 Received: from cosworth.uk.xensource.com (cosworth.uk.xensource.com [10.80.16.52]) by smtp01.ad.xensource.com (8.13.1/8.13.1) with ESMTP id q0PCRFqU005662; Wed, 25 Jan 2012 04:27:19 -0800 From: Ian Campbell To: netdev@vger.kernel.org CC: Ian Campbell , "David S. Miller" , Eric Dumazet , =?UTF-8?q?Micha=C5=82=20Miros=C5=82aw?= Subject: [PATCH v3 3/6] net: add support for per-paged-fragment destructors Date: Wed, 25 Jan 2012 12:27:11 +0000 Message-ID: <1327494434-21566-3-git-send-email-ian.campbell@citrix.com> X-Mailer: git-send-email 1.7.2.5 In-Reply-To: <1327494389.24561.316.camel@zakaz.uk.xensource.com> References: <1327494389.24561.316.camel@zakaz.uk.xensource.com> MIME-Version: 1.0 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Entities which care about the complete lifecycle of pages which they inject into the network stack via an skb paged fragment can choose to set this destructor in order to receive a callback when the stack is really finished with a page (including all clones, retransmits, pull-ups etc etc). This destructor will always be propagated alongside the struct page when copying skb_frag_t->page. This is the reason I chose to embed the destructor in a "struct { } page" within the skb_frag_t, rather than as a separate field, since it allows existing code which propagates ->frags[N].page to Just Work(tm). When the destructor is present the page reference counting is done slightly differently. No references are held by the network stack on the struct page (it is up to the caller to manage this as necessary) instead the network stack will track references via the count embedded in the destructor structure. When this reference count reaches zero then the destructor will be called and the caller can take the necesary steps to release the page (i.e. release the struct page reference itself). The intention is that callers can use this callback to delay completion to _their_ callers until the network stack has completely released the page, in order to prevent use-after-free or modification of data pages which are still in use by the stack. It is allowable (indeed expected) for a caller to share a single destructor instance between multiple pages injected into the stack e.g. a group of pages included in a single higher level operation might share a destructor which is used to complete that higher level operation. With this change and the previous two changes to shinfo alignment and field orderring it is now the case tyhat on a 64 bit system with 64 byte cache lines, everything from nr_frags until the end of frags[0] is on the same cacheline. Signed-off-by: Ian Campbell Cc: "David S. Miller" Cc: Eric Dumazet Cc: "Michał Mirosław" Cc: netdev@vger.kernel.org --- include/linux/skbuff.h | 43 +++++++++++++++++++++++++++++++++++++++++++ net/core/skbuff.c | 17 +++++++++++++++++ 2 files changed, 60 insertions(+), 0 deletions(-) diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 7b82ed1..df2b93f 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -143,9 +143,15 @@ struct sk_buff; typedef struct skb_frag_struct skb_frag_t; +struct skb_frag_destructor { + atomic_t ref; + int (*destroy)(struct skb_frag_destructor *destructor); +}; + struct skb_frag_struct { struct { struct page *p; + struct skb_frag_destructor *destructor; } page; #if (BITS_PER_LONG > 32) || (PAGE_SIZE >= 65536) __u32 page_offset; @@ -1177,6 +1183,31 @@ static inline int skb_pagelen(const struct sk_buff *skb) } /** + * skb_frag_set_destructor - set destructor for a paged fragment + * @skb: buffer containing fragment to be initialised + * @i: paged fragment index to initialise + * @destroy: the destructor to use for this fragment + * + * Sets @destroy as the destructor to be called when all references to + * the frag @i in @skb (tracked over skb_clone, retransmit, pull-ups, + * etc) are released. + * + * When a destructor is set then reference counting is performed on + * @destroy->ref. When the ref reaches zero then @destroy->destroy + * will be called. The caller is responsible for holding and managing + * any other references (such a the struct page reference count). + * + * This function must be called before any use of skb_frag_ref() or + * skb_frag_unref(). + */ +static inline void skb_frag_set_destructor(struct sk_buff *skb, int i, + struct skb_frag_destructor *destroy) +{ + skb_frag_t *frag = &skb_shinfo(skb)->frags[i]; + frag->page.destructor = destroy; +} + +/** * __skb_fill_page_desc - initialise a paged fragment in an skb * @skb: buffer containing fragment to be initialised * @i: paged fragment index to initialise @@ -1195,6 +1226,7 @@ static inline void __skb_fill_page_desc(struct sk_buff *skb, int i, skb_frag_t *frag = &skb_shinfo(skb)->frags[i]; frag->page.p = page; + frag->page.destructor = NULL; frag->page_offset = off; skb_frag_size_set(frag, size); } @@ -1689,6 +1721,9 @@ static inline struct page *skb_frag_page(const skb_frag_t *frag) return frag->page.p; } +extern void skb_frag_destructor_ref(struct skb_frag_destructor *destroy); +extern void skb_frag_destructor_unref(struct skb_frag_destructor *destroy); + /** * __skb_frag_ref - take an addition reference on a paged fragment. * @frag: the paged fragment @@ -1697,6 +1732,10 @@ static inline struct page *skb_frag_page(const skb_frag_t *frag) */ static inline void __skb_frag_ref(skb_frag_t *frag) { + if (unlikely(frag->page.destructor)) { + skb_frag_destructor_ref(frag->page.destructor); + return; + } get_page(skb_frag_page(frag)); } @@ -1720,6 +1759,10 @@ static inline void skb_frag_ref(struct sk_buff *skb, int f) */ static inline void __skb_frag_unref(skb_frag_t *frag) { + if (unlikely(frag->page.destructor)) { + skb_frag_destructor_unref(frag->page.destructor); + return; + } put_page(skb_frag_page(frag)); } diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 934a9b4..766b760 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -354,6 +354,23 @@ struct sk_buff *dev_alloc_skb(unsigned int length) } EXPORT_SYMBOL(dev_alloc_skb); +void skb_frag_destructor_ref(struct skb_frag_destructor *destroy) +{ + BUG_ON(destroy == NULL); + atomic_inc(&destroy->ref); +} +EXPORT_SYMBOL(skb_frag_destructor_ref); + +void skb_frag_destructor_unref(struct skb_frag_destructor *destroy) +{ + if (destroy == NULL) + return; + + if (atomic_dec_and_test(&destroy->ref)) + destroy->destroy(destroy); +} +EXPORT_SYMBOL(skb_frag_destructor_unref); + static void skb_drop_list(struct sk_buff **listp) { struct sk_buff *list = *listp;