From: David Miller <davem@davemloft.net>
To: kuba@kernel.org
Cc: netdev@vger.kernel.org, paulmck@kernel.org,
joel@joelfernandes.org, josh@joshtriplett.org,
peterz@infradead.org, christian.brauner@ubuntu.com,
rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
nikolay@cumulusnetworks.com, sfr@canb.auug.org.au,
roopa@nvidia.com
Subject: Re: [PATCH net-next] rcu: prevent RCU_LOCKDEP_WARN() from swallowing the condition
Date: Tue, 08 Sep 2020 20:12:40 -0700 (PDT) [thread overview]
Message-ID: <20200908.201240.821919587285621499.davem@davemloft.net> (raw)
In-Reply-To: <20200908173624.160024-1-kuba@kernel.org>
From: Jakub Kicinski <kuba@kernel.org>
Date: Tue, 8 Sep 2020 10:36:24 -0700
> We run into a unused variable warning in bridge code when
> variable is only used inside the condition of
> rcu_dereference_protected().
>
> #define mlock_dereference(X, br) \
> rcu_dereference_protected(X, lockdep_is_held(&br->multicast_lock))
>
> Since on builds with CONFIG_PROVE_RCU=n rcu_dereference_protected()
> compiles to nothing the compiler doesn't see the variable use.
>
> Prevent the warning by adding the condition as dead code.
> We need to un-hide the declaration of lockdep_tasklist_lock_is_held()
> and fix a bug the crept into a net/sched header.
>
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
I ended up applying Nikolay's fix, but this situation with the rcu macros
needs to be addressed.
prev parent reply other threads:[~2020-09-09 3:12 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200908090049.7e528e7f@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
2020-09-08 17:36 ` [PATCH net-next] rcu: prevent RCU_LOCKDEP_WARN() from swallowing the condition Jakub Kicinski
2020-09-08 18:15 ` nikolay
2020-09-09 0:27 ` Jakub Kicinski
2020-09-14 20:21 ` Joel Fernandes
2020-09-14 22:47 ` Jakub Kicinski
2020-09-15 0:20 ` Paul E. McKenney
2020-09-15 0:30 ` Jakub Kicinski
2020-09-15 17:02 ` Paul E. McKenney
2020-09-15 1:34 ` Joel Fernandes
2020-09-09 3:12 ` David Miller [this message]
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