RE: [PATCH v2 6/7] apei/ghes: Use unrcu_pointer for cmpxchg

[David Laight <David.Laight@ACULAB.COM>]

From: Jia He
> Sent: 17 August 2022 15:35
> 
> ghes_estatus_caches should be add rcu annotation to avoid sparse warnings.
>    drivers/acpi/apei/ghes.c:733:25: sparse: sparse: incompatible types in comparison expression
> (different address spaces):
>    drivers/acpi/apei/ghes.c:733:25: sparse:    struct ghes_estatus_cache [noderef] __rcu *
>    drivers/acpi/apei/ghes.c:733:25: sparse:    struct ghes_estatus_cache *
>    drivers/acpi/apei/ghes.c:813:25: sparse: sparse: incompatible types in comparison expression
> (different address spaces):
>    drivers/acpi/apei/ghes.c:813:25: sparse:    struct ghes_estatus_cache [noderef] __rcu *
>    drivers/acpi/apei/ghes.c:813:25: sparse:    struct ghes_estatus_cache *
> 
> unrcu_pointer is to strip the __rcu in cmpxchg.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Jia He <justin.he@arm.com>
> ---
>  drivers/acpi/apei/ghes.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
> index 9272d963b57d..92ae58f4f7bb 100644
> --- a/drivers/acpi/apei/ghes.c
> +++ b/drivers/acpi/apei/ghes.c
> @@ -144,7 +144,7 @@ struct ghes_vendor_record_entry {
>  static struct gen_pool *ghes_estatus_pool;
>  static unsigned long ghes_estatus_pool_size_request;
> 
> -static struct ghes_estatus_cache *ghes_estatus_caches[GHES_ESTATUS_CACHES_SIZE];
> +static struct ghes_estatus_cache __rcu *ghes_estatus_caches[GHES_ESTATUS_CACHES_SIZE];
>  static atomic_t ghes_estatus_cache_alloced;
> 
>  static int ghes_panic_timeout __read_mostly = 30;
> @@ -834,8 +834,9 @@ static void ghes_estatus_cache_add(
>  	}
>  	/* new_cache must be put into array after its contents are written */
>  	smp_wmb();
> -	if (slot != -1 && cmpxchg(ghes_estatus_caches + slot,
> -				  slot_cache, new_cache) == slot_cache) {
> +	if (slot != -1 && unrcu_pointer(cmpxchg(ghes_estatus_caches + slot,
> +				RCU_INITIALIZER(slot_cache),
> +				RCU_INITIALIZER(new_cache)))) {

Did you test this?
There seems to be an == missing.

	David

>  		if (slot_cache)
>  			call_rcu(&slot_cache->rcu, ghes_estatus_cache_rcu_free);
>  	} else
> --
> 2.25.1

-
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