linux-kernel - Re: [PATCH v2] PM: EM: Address RCU-related sparse warnings

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Message-ID: <4a538376-bf74-4c51-bfa8-a86f67790662@arm.com>
Date: Fri, 7 Mar 2025 13:02:50 +0000
From: Lukasz Luba <lukasz.luba@....com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: LKML <linux-kernel@...r.kernel.org>, Linux PM <linux-pm@...r.kernel.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Subject: Re: [PATCH v2] PM: EM: Address RCU-related sparse warnings



On 3/6/25 16:49, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> The usage of __rcu in the Energy Model code is quite inconsistent
> which causes the following sparse warnings to trigger:
> 
> kernel/power/energy_model.c:169:15: warning: incorrect type in assignment (different address spaces)
> kernel/power/energy_model.c:169:15:    expected struct em_perf_table [noderef] __rcu *table
> kernel/power/energy_model.c:169:15:    got struct em_perf_table *
> kernel/power/energy_model.c:171:9: warning: incorrect type in argument 1 (different address spaces)
> kernel/power/energy_model.c:171:9:    expected struct callback_head *head
> kernel/power/energy_model.c:171:9:    got struct callback_head [noderef] __rcu *
> kernel/power/energy_model.c:171:9: warning: cast removes address space '__rcu' of expression
> kernel/power/energy_model.c:182:19: warning: incorrect type in argument 1 (different address spaces)
> kernel/power/energy_model.c:182:19:    expected struct kref *kref
> kernel/power/energy_model.c:182:19:    got struct kref [noderef] __rcu *
> kernel/power/energy_model.c:200:15: warning: incorrect type in assignment (different address spaces)
> kernel/power/energy_model.c:200:15:    expected struct em_perf_table [noderef] __rcu *table
> kernel/power/energy_model.c:200:15:    got void *[assigned] _res
> kernel/power/energy_model.c:204:20: warning: incorrect type in argument 1 (different address spaces)
> kernel/power/energy_model.c:204:20:    expected struct kref *kref
> kernel/power/energy_model.c:204:20:    got struct kref [noderef] __rcu *
> kernel/power/energy_model.c:320:19: warning: incorrect type in argument 1 (different address spaces)
> kernel/power/energy_model.c:320:19:    expected struct kref *kref
> kernel/power/energy_model.c:320:19:    got struct kref [noderef] __rcu *
> kernel/power/energy_model.c:325:45: warning: incorrect type in argument 2 (different address spaces)
> kernel/power/energy_model.c:325:45:    expected struct em_perf_state *table
> kernel/power/energy_model.c:325:45:    got struct em_perf_state [noderef] __rcu *
> kernel/power/energy_model.c:425:45: warning: incorrect type in argument 3 (different address spaces)
> kernel/power/energy_model.c:425:45:    expected struct em_perf_state *table
> kernel/power/energy_model.c:425:45:    got struct em_perf_state [noderef] __rcu *
> kernel/power/energy_model.c:442:15: warning: incorrect type in argument 1 (different address spaces)
> kernel/power/energy_model.c:442:15:    expected void const *objp
> kernel/power/energy_model.c:442:15:    got struct em_perf_table [noderef] __rcu *[assigned] em_table
> kernel/power/energy_model.c:626:55: warning: incorrect type in argument 2 (different address spaces)
> kernel/power/energy_model.c:626:55:    expected struct em_perf_state *table
> kernel/power/energy_model.c:626:55:    got struct em_perf_state [noderef] __rcu *
> kernel/power/energy_model.c:681:16: warning: incorrect type in assignment (different address spaces)
> kernel/power/energy_model.c:681:16:    expected struct em_perf_state *new_ps
> kernel/power/energy_model.c:681:16:    got struct em_perf_state [noderef] __rcu *
> kernel/power/energy_model.c:699:37: warning: incorrect type in argument 2 (different address spaces)
> kernel/power/energy_model.c:699:37:    expected struct em_perf_state *table
> kernel/power/energy_model.c:699:37:    got struct em_perf_state [noderef] __rcu *
> kernel/power/energy_model.c:733:38: warning: incorrect type in argument 3 (different address spaces)
> kernel/power/energy_model.c:733:38:    expected struct em_perf_state *table
> kernel/power/energy_model.c:733:38:    got struct em_perf_state [noderef] __rcu *
> kernel/power/energy_model.c:855:53: warning: dereference of noderef expression
> kernel/power/energy_model.c:864:32: warning: dereference of noderef expression
> 
> This is because the __rcu annotation for sparse is only applicable to
> pointers that need rcu_dereference() or equivalent for protection, which
> basically means pointers assigned with rcu_assign_pointer().
> 
> Make all of the above sparse warnings go away by cleaning up the usage
> of __rcu and using rcu_dereference_protected() where applicable.
> 
> Cc: All applicable <stable@...r.kernel.org>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> 
> This replaces
> 
> https://lore.kernel.org/linux-pm/1929404.tdWV9SEqCh@rjwysocki.net/
> 
> and
> 
> https://lore.kernel.org/linux-pm/13728396.uLZWGnKmhe@rjwysocki.net/
> 
> ---
>   include/linux/energy_model.h |   12 ++++++------
>   kernel/power/energy_model.c  |   39 ++++++++++++++++++++-------------------
>   2 files changed, 26 insertions(+), 25 deletions(-)
> 

LGTM,

Reviewed-by: Lukasz Luba <lukasz.luba@....com>