linux-kernel - Re: [PATCH RFC net-next v2 7/7] net: skbuff: always try to recycle PP pages directly when in softirq

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Message-ID: <20230721090129.4a61033b@kernel.org>
Date:   Fri, 21 Jul 2023 09:01:29 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Alexander Lobakin <aleksander.lobakin@...el.com>,
        Yunsheng Lin <linyunsheng@...wei.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Larysa Zaremba <larysa.zaremba@...el.com>,
        Alexander Duyck <alexanderduyck@...com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC net-next v2 7/7] net: skbuff: always try to recycle
 PP pages directly when in softirq

On Fri, 21 Jul 2023 17:37:57 +0200 Alexander Lobakin wrote:
> > Does it mean ptr_ring_produce_any() is needed in
> > page_pool_recycle_in_ring() too?
> > 
> > As it is assumed that page pool API can be called in the context with
> > irqs_disabled() || in_hardirq(), and force recylcling happens in the
> > prt_ring.
> > 
> > Isn't it conflit with the below patch? as the below patch assume page
> > pool API can not be called in the context with irqs_disabled() || in_hardirq():
> > [PATCH net-next] page_pool: add a lockdep check for recycling in hardirq
> > 
> > Or am I missing something obvious here?  
> 
> No, Page Pool is *not* intended to be called when IRQs are disabled,
> hence the fix Jakub's posted in the separate thread.

Yeah, it's just a bandaid / compromise, since Olek really wants his
optimization and I really don't want to spend a month debugging
potential production crashes :)

On the ptr ring the use may still be incorrect but there is a spin lock
so things will explode in much more obvious way, if they do.