Re: [PATCH net-next] page_pool: add debug for release to cache from wrong CPU

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2025-09-18 11:48:21 [+0300], Dragos Tatulea wrote:
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index ba70569bd4b0..404064d893d6 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -768,6 +795,18 @@ static bool page_pool_recycle_in_cache(netmem_ref netmem,
>  		return false;
>  	}
>  
> +#ifdef CONFIG_DEBUG_PAGE_POOL_CACHE_RELEASE
> +	if (unlikely(!page_pool_napi_local(pool))) {

if you do IS_ENABLED(CONFIG_DEBUG_PAGE_POOL_CACHE_RELEASE) you could
avoid the ifdef.

A quick question, where is this allow_direct argument supposed to come
from? I just noticed that mlx5 does
   page_pool_put_unrefed_netmem(, true);

which then does not consider page_pool_napi_local(). But your proposed
change here will complain as it should.

> +		u32 pp_cpuid = READ_ONCE(pool->cpuid);
> +		u32 cpuid = smp_processor_id();
> +
> +		WARN_RATELIMIT(1, "page_pool %d: direct page release from wrong CPU %d, expected CPU %d",
> +			       pool->user.id, cpuid, pp_cpuid);
> +
> +		return false;
> +	}
> +#endif
> +
>  	/* Caller MUST have verified/know (page_ref_count(page) == 1) */
>  	pool->alloc.cache[pool->alloc.count++] = netmem;
>  	recycle_stat_inc(pool, cached);

Sebastian