From:   Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
To:     Jesper Dangaard Brouer <brouer@redhat.com>,
        Amol Grover <frextrite@gmail.com>
Cc:     brouer@redhat.com, Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        "David S . Miller" <davem@davemloft.net>,
        Jakub Kicinski <jakub.kicinski@netronome.com>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        John Fastabend <john.fastabend@gmail.com>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        Andrii Nakryiko <andriin@fb.com>, netdev@vger.kernel.org,
        bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-kernel-mentees@lists.linuxfoundation.org,
        Joel Fernandes <joel@joelfernandes.org>,
        Madhuparna Bhowmik <madhuparnabhowmik04@gmail.com>,
        "Paul E . McKenney" <paulmck@kernel.org>
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>
Date:   Thu, 23 Jan 2020 14:42:03 +0100
Message-ID: <87a76e9tn8.fsf@toke.dk>
MIME-Version: 1.0
Content-Type: text/plain
Sender: bpf-owner@vger.kernel.org
Precedence: bulk

Jesper Dangaard Brouer <brouer@redhat.com> writes:

> On Thu, 23 Jan 2020 17:34:38 +0530
> Amol Grover <frextrite@gmail.com> 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