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

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Message-ID: <20200221175436.GB2181@nanopsycho>
Date:   Fri, 21 Feb 2020 18:54:36 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
Cc:     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

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()