From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755418Ab3EUSMh (ORCPT ); Tue, 21 May 2013 14:12:37 -0400 Received: from forward-corp1g.mail.yandex.net ([95.108.253.251]:47697 "EHLO forward-corp1g.mail.yandex.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754895Ab3EUSMf (ORCPT ); Tue, 21 May 2013 14:12:35 -0400 Authentication-Results: smtpcorp4.mail.yandex.net; dkim=pass header.i=@yandex-team.ru Message-ID: <519BB90B.6080706@yandex-team.ru> Date: Tue, 21 May 2013 22:12:27 +0400 From: Roman Gushchin User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130510 Thunderbird/17.0.6 MIME-Version: 1.0 To: Eric Dumazet CC: paulmck@linux.vnet.ibm.com, Dipankar Sarma , zhmurov@yandex-team.ru, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, "David S. Miller" , Alexey Kuznetsov , James Morris , Hideaki YOSHIFUJI , Patrick McHardy Subject: Re: [PATCH v2] rcu: fix a race in hlist_nulls_for_each_entry_rcu macro References: <519B38EC.90401@yandex-team.ru> <20130521120906.GD3578@linux.vnet.ibm.com> <1369143885.3301.221.camel@edumazet-glaptop> <519B8908.9080007@yandex-team.ru> <1369150693.3301.233.camel@edumazet-glaptop> In-Reply-To: <1369150693.3301.233.camel@edumazet-glaptop> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > If other rcu accessors have the same problem, a more complete patch is > needed. [PATCH] rcu: fix a race in rcu lists traverse macros Some network functions (udp4_lib_lookup2(), for instance) use the rcu lists traverse macros (hlist_nulls_for_each_entry_rcu, for instance) in a way that assumes restarting of a loop. In this case, it is strictly necessary to reread the head->first value from the memory before each scan. Without additional hints, gcc caches this value in a register. In this case, if a cached node is moved to another chain during the scan, we can loop forever getting wrong nulls values and restarting the loop uninterruptedly. Signed-off-by: Roman Gushchin Reported-by: Boris Zhmurov --- include/linux/compiler.h | 6 ++++++ include/linux/rculist.h | 6 ++++-- include/linux/rculist_nulls.h | 3 ++- 3 files changed, 12 insertions(+), 3 deletions(-) diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 92669cd..0e05d7c 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -351,6 +351,12 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect); */ #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) +/* + * Prevent the compiler from optimizing accesses to structure member. + */ +#define GET_STRUCT_FIELD_VOLATILE(struct_ptr, field) \ + (((volatile typeof(*struct_ptr) *)struct_ptr)->field) + /* Ignore/forbid kprobes attach on very low level functions marked by this attribute: */ #ifdef CONFIG_KPROBES # define __kprobes __attribute__((__section__(".kprobes.text"))) diff --git a/include/linux/rculist.h b/include/linux/rculist.h index 8089e35..6c3eea7 100644 --- a/include/linux/rculist.h +++ b/include/linux/rculist.h @@ -282,7 +282,8 @@ static inline void list_splice_init_rcu(struct list_head *list, * as long as the traversal is guarded by rcu_read_lock(). */ #define list_for_each_entry_rcu(pos, head, member) \ - for (pos = list_entry_rcu((head)->next, typeof(*pos), member); \ + for (pos = list_entry_rcu(GET_STRUCT_FIELD_VOLATILE(head, next), \ + typeof(*pos), member); \ &pos->member != (head); \ pos = list_entry_rcu(pos->member.next, typeof(*pos), member)) @@ -348,7 +349,8 @@ static inline void hlist_replace_rcu(struct hlist_node *old, /* * return the first or the next element in an RCU protected hlist */ -#define hlist_first_rcu(head) (*((struct hlist_node __rcu **)(&(head)->first))) +#define hlist_first_rcu(head) (*((struct hlist_node __rcu **) \ + (&GET_STRUCT_FIELD_VOLATILE(head, first)))) #define hlist_next_rcu(node) (*((struct hlist_node __rcu **)(&(node)->next))) #define hlist_pprev_rcu(node) (*((struct hlist_node __rcu **)((node)->pprev))) diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h index 2ae1371..b04fd0a 100644 --- a/include/linux/rculist_nulls.h +++ b/include/linux/rculist_nulls.h @@ -38,7 +38,8 @@ static inline void hlist_nulls_del_init_rcu(struct hlist_nulls_node *n) } #define hlist_nulls_first_rcu(head) \ - (*((struct hlist_nulls_node __rcu __force **)&(head)->first)) + (*((struct hlist_nulls_node __rcu __force **) \ + &(GET_STRUCT_FIELD_VOLATILE(head, first)))) #define hlist_nulls_next_rcu(node) \ (*((struct hlist_nulls_node __rcu __force **)&(node)->next)) -- 1.8.1.2