netdev - Re: [PATCH] net: core: devlink.c: Use built-in RCU list checking

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Date:   Fri, 21 Feb 2020 23:30:15 +0530
From:   Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
To:     Jiri Pirko <jiri@...nulli.us>, y@...huparna-HP-Notebook
Cc:     Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>,
        jiri@...lanox.com, davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, joel@...lfernandes.org,
        frextrite@...il.com,
        linux-kernel-mentees@...ts.linuxfoundation.org, paulmck@...nel.org
Subject: Re: [PATCH] net: core: devlink.c: Use built-in RCU list checking

On Fri, Feb 21, 2020 at 06:54:36PM +0100, Jiri Pirko wrote:
> Fri, Feb 21, 2020 at 06:35:34PM CET, madhuparnabhowmik10@...il.com wrote:
> >On Fri, Feb 21, 2020 at 06:20:08PM +0100, Jiri Pirko wrote:
> >> Fri, Feb 21, 2020 at 05:51:41PM CET, madhuparnabhowmik10@...il.com wrote:
> >> >From: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
> >> >
> >> >list_for_each_entry_rcu() has built-in RCU and lock checking.
> >> >
> >> >Pass cond argument to list_for_each_entry_rcu() to silence
> >> >false lockdep warning when CONFIG_PROVE_RCU_LIST is enabled
> >> >by default.
> >> >
> >> >Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
> >> 
> >> Reviewed-by: Jiri Pirko <jiri@...lanox.com>
> >> 
> >> Thanks.
> >> 
> >> However, there is a callpath where not devlink lock neither rcu read is
> >> taken:
> >> devlink_dpipe_table_register()->devlink_dpipe_table_find()
> >>
> >Hi,
> >
> >Yes I had noticed this, but I was not sure if there is some other lock
> >which is being used.
> >
> >If yes, then can you please tell me which lock is held in this case,
> >and I can add that condition as well to list_for_each_entry_rcu() usage.
> >
> >And if no lock or rcu_read_lock is held then may be we should
> >use rcu_read_lock/unlock here.
> >
> >Let me know what you think about this.
> 
> devlink->lock should be held since the beginning of
> devlink_dpipe_table_register()
>
Alright, I will send a patch with this change soon.
Thank you for the help.

Regards,
Madhuparna