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

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Date:   Sun, 23 Feb 2020 19:19:34 +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

Sun, Feb 23, 2020 at 12:03:42PM 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()
>> I guess that was not the trace you were seeing, right?
>> 
>> 
>> >---
>> > net/core/devlink.c | 3 ++-
>> > 1 file changed, 2 insertions(+), 1 deletion(-)
>> >
>> >diff --git a/net/core/devlink.c b/net/core/devlink.c
>> >index 4c63c9a4c09e..3e8c94155d93 100644
>> >--- a/net/core/devlink.c
>> >+++ b/net/core/devlink.c
>> >@@ -2107,7 +2107,8 @@ devlink_dpipe_table_find(struct list_head *dpipe_tables,
>> > {
>> > 	struct devlink_dpipe_table *table;
>> > 
>> >-	list_for_each_entry_rcu(table, dpipe_tables, list) {
>> >+	list_for_each_entry_rcu(table, dpipe_tables, list,
>> >+				lockdep_is_held(&devlink->lock)) {
>
>Hi Jiri,
>
>I just noticed that this patch does not compile because devlink is
>not passed as an argument to devlink_dpipe_table_find() and it is not
>even global. I am not sure why I didn't encounter this error before
>sending the patch. Anyway, I am sorry about this.
>But it seems to be the right lock that should be held and checked for
>in devlink_dpipe_table_find(). 
>So will it be okay to pass devlink to devlink_dpipe_table_find()?

Sure.

>Anyway devlink_dpipe_table_find() is only called from functions
>within devlink.c.
>
>Let me know what you think about this.
>Thank you,
>Madhuparna
>
>
>> > 		if (!strcmp(table->name, table_name))
>> > 			return table;
>> > 	}
>> >-- 
>> >2.17.1
>> >