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

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Message-ID: <20250918091341.n6_OgbOW@linutronix.de>
Date: Thu, 18 Sep 2025 11:13:41 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Dragos Tatulea <dtatulea@...dia.com>
Cc: Jesper Dangaard Brouer <hawk@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Ilias Apalodimas <ilias.apalodimas@...aro.org>,
	Clark Williams <clrkwllms@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>, netdev@...r.kernel.org,
	Tariq Toukan <tariqt@...dia.com>, linux-kernel@...r.kernel.org,
	linux-rt-devel@...ts.linux.dev
Subject: Re: [PATCH net-next] page_pool: add debug for release to cache from
 wrong CPU

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