netdev - Re: [PATCH] net: xen-netbank: hash.c: Use built-in RCU list checking

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Date:   Wed, 15 Jan 2020 15:04:26 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Madhuparna Bhowmik <madhuparnabhowmik04@...il.com>
Cc:     Wei Liu <wei.liu@...nel.org>, paul@....org, davem@...emloft.net,
        xen-devel@...ts.xenproject.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Amol Grover <frextrite@...il.com>,
        linux-kernel-mentees@...ts.linuxfoundation.org
Subject: Re: [PATCH] net: xen-netbank: hash.c: Use built-in RCU list checking

On Wed, Jan 15, 2020 at 07:36:38PM +0530, Madhuparna Bhowmik wrote:
[...]
> 
> > The surrounding code makes it pretty clear that the lock is already held
> > by the time list_for_each_entry_rcu is called, yet the checking involved
> > in lockdep_is_held is not trivial, so I'm afraid I don't consider this a
> > strict improvement over the existing code.
> >
> > Actually,  we want to make CONFIG_PROVE_LIST_RCU enabled by default.

I think you meant CONFIG_PROVE_RCU_LIST.

> And if the cond argument is not passed when the usage of
> list_for_each_entry_rcu()
> is outside of rcu_read_lock(), it will lead to a false positive.
> Therefore, I think this patch is required.

Fair enough.

Wei.