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Miller" , Jakub Kicinski , Jesper Dangaard Brouer , John Fastabend , Martin KaFai Lau , Song Liu , Yonghong Song , Andrii Nakryiko , netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kernel-mentees@lists.linuxfoundation.org, Joel Fernandes , Madhuparna Bhowmik , "Paul E . McKenney" Subject: Re: [PATCH] bpf: devmap: Pass lockdep expression to RCU lists In-Reply-To: <20200123143725.036140e7@carbon> References: <20200123120437.26506-1-frextrite@gmail.com> <20200123143725.036140e7@carbon> X-Clacks-Overhead: GNU Terry Pratchett Date: Thu, 23 Jan 2020 14:42:03 +0100 Message-ID: <87a76e9tn8.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Jesper Dangaard Brouer writes: > On Thu, 23 Jan 2020 17:34:38 +0530 > Amol Grover wrote: > >> head is traversed using hlist_for_each_entry_rcu outside an >> RCU read-side critical section but under the protection >> of dtab->index_lock. > > We do hold the lock in update and delete cases, but not in the lookup > cases. Is it then still okay to add the lockdep_is_held() annotation? I concluded 'yes' from the comment on hlist_for_each_entry_rcu(): The lockdep condition gets passed to this: #define __list_check_rcu(dummy, cond, extra...) \ ({ \ check_arg_count_one(extra); \ RCU_LOCKDEP_WARN(!cond && !rcu_read_lock_any_held(), \ "RCU-list traversed in non-reader section!"); \ }) so that seems fine :) -Toke