netdev - Re: [PATCH net-next] net: wwan: t7xx: fix GFP_KERNEL usage in spin

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Date:   Mon, 16 May 2022 23:36:04 +0300
From:   Sergey Ryazanov <ryazanov.s.a@...il.com>
To:     Ziyang Xuan <william.xuanziyang@...wei.com>
Cc:     "Devegowda, Chandrashekar" <chandrashekar.devegowda@...el.com>,
        Intel Corporation <linuxwwan@...el.com>,
        chiranjeevi.rapolu@...ux.intel.com,
        Haijun Liu (刘海军) 
        <haijun.liu@...iatek.com>,
        M Chetan Kumar <m.chetan.kumar@...ux.intel.com>,
        Ricardo Martinez <ricardo.martinez@...ux.intel.com>,
        Loic Poulain <loic.poulain@...aro.org>,
        David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] net: wwan: t7xx: fix GFP_KERNEL usage in
 spin_lock context

Hello Ziyang,

On Sat, May 14, 2022 at 11:57 AM Ziyang Xuan
<william.xuanziyang@...wei.com> wrote:
> t7xx_cldma_clear_rxq() call t7xx_cldma_alloc_and_map_skb() in spin_lock
> context, But __dev_alloc_skb() in t7xx_cldma_alloc_and_map_skb() uses
> GFP_KERNEL, that will introduce scheduling factor in spin_lock context.
>
> Replace GFP_KERNEL with GFP_ATOMIC to fix it.

Would not it will be more reliable to just rework
t7xx_cldma_clear_rxq() to avoid calling t7xx_cldma_alloc_and_map_skb()
under the spin lock instead of doing each allocation with GFP_ATOMIC?
E.g. t7xx_cldma_gpd_rx_from_q() calls t7xx_cldma_alloc_and_map_skb()
avoiding any lock holding.

-- 
Sergey