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[24.43.226.3]) by smtp.gmail.com with ESMTPSA id l26sm492514pgn.46.2020.02.19.11.35.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 19 Feb 2020 11:35:24 -0800 (PST) Subject: Re: [PATCH] tcp: Pass lockdep expression to RCU lists To: Amol Grover , Eric Dumazet , "David S . Miller" , Alexey Kuznetsov , Hideaki YOSHIFUJI , Jakub Kicinski Cc: linux-kernel@vger.kernel.org, linux-kernel-mentees@lists.linuxfoundation.org, Joel Fernandes , Madhuparna Bhowmik , "Paul E . McKenney" , netdev@vger.kernel.org References: <20200219100545.27397-1-frextrite@gmail.com> From: Eric Dumazet Message-ID: Date: Wed, 19 Feb 2020 11:35:21 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200219100545.27397-1-frextrite@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2/19/20 2:05 AM, Amol Grover wrote: > tcp_cong_list is traversed using list_for_each_entry_rcu > outside an RCU read-side critical section but under the protection > of tcp_cong_list_lock. > This is not true. There are cases where RCU read lock is held, and others where the tcp_cong_list_lock is held. I believe you need to be more precise in the changelog. If there was a bug, net tree would be the target for this patch, with a required Fixes: tag. Otherwise, if net-next tree is the intended target, you have to signal it, as instructed in Documentation/networking/netdev-FAQ.rst Thanks. > Hence, add corresponding lockdep expression to silence false-positive > warnings, and harden RCU lists. > > Signed-off-by: Amol Grover > --- > net/ipv4/tcp_cong.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c > index 3737ec096650..8d4446ed309e 100644 > --- a/net/ipv4/tcp_cong.c > +++ b/net/ipv4/tcp_cong.c > @@ -25,7 +25,8 @@ static struct tcp_congestion_ops *tcp_ca_find(const char *name) > { > struct tcp_congestion_ops *e; > > - list_for_each_entry_rcu(e, &tcp_cong_list, list) { > + list_for_each_entry_rcu(e, &tcp_cong_list, list, > + lockdep_is_held(&tcp_cong_list_lock)) { > if (strcmp(e->name, name) == 0) > return e; > } > @@ -55,7 +56,8 @@ struct tcp_congestion_ops *tcp_ca_find_key(u32 key) > { > struct tcp_congestion_ops *e; > > - list_for_each_entry_rcu(e, &tcp_cong_list, list) { > + list_for_each_entry_rcu(e, &tcp_cong_list, list, > + lockdep_is_held(&tcp_cong_list_lock)) { > if (e->key == key) > return e; > } > @@ -317,7 +319,8 @@ int tcp_set_allowed_congestion_control(char *val) > } > > /* pass 2 clear old values */ > - list_for_each_entry_rcu(ca, &tcp_cong_list, list) > + list_for_each_entry_rcu(ca, &tcp_cong_list, list, > + lockdep_is_held(&tcp_cong_list_lock)) > ca->flags &= ~TCP_CONG_NON_RESTRICTED; > > /* pass 3 mark as allowed */ >