netdev - Re: [BUG] Possible unsafe page

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Message-ID: <55079677-9139-2f68-fe4c-053020b6f33f@kernel.org>
Date: Fri, 25 Aug 2023 15:16:07 +0200
From: Jesper Dangaard Brouer <hawk@...nel.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 netdev@...r.kernel.org, Ratheesh Kannoth <rkannoth@...vell.com>
Cc: hawk@...nel.org, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Geetha sowjanya <gakula@...vell.com>,
 Ilias Apalodimas <ilias.apalodimas@...aro.org>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Subbaraya Sundeep <sbhatta@...vell.com>, Sunil Goutham
 <sgoutham@...vell.com>, Thomas Gleixner <tglx@...utronix.de>,
 hariprasad <hkelam@...vell.com>,
 Alexander Lobakin <aleksander.lobakin@...el.com>,
 Qingfang DENG <qingfang.deng@...lower.com.cn>
Subject: Re: [BUG] Possible unsafe page_pool usage in octeontx2

On 23/08/2023 21.45, Jesper Dangaard Brouer wrote:
> On 23/08/2023 11.47, Sebastian Andrzej Siewior wrote:
[...]
>>
>> This breaks in octeontx2 where a worker is used to fill the buffer:
>>    otx2_pool_refill_task() -> otx2_alloc_rbuf() -> __otx2_alloc_rbuf() ->
>>    otx2_alloc_pool_buf() -> page_pool_alloc_frag().
>>
> 
> This seems problematic! - this is NOT allowed.
> 
> But otx2_pool_refill_task() is a work-queue, and I though it runs in
> process-context.  This WQ process is not allowed to use the lockless PP
> cache.  This seems to be a bug!
> 
> The problematic part is otx2_alloc_rbuf() that disables BH:
> 
>   int otx2_alloc_rbuf(struct otx2_nic *pfvf, struct otx2_pool *pool,
>              dma_addr_t *dma)
>   {
>      int ret;
> 
>      local_bh_disable();
>      ret = __otx2_alloc_rbuf(pfvf, pool, dma);
>      local_bh_enable();
>      return ret;
>   }
> 
> The fix, can be to not do this local_bh_disable() in this driver?

Correcting myself. It is not a fix to remove this local_bh_disable().
(which is obvious now I read the code again).

This WQ process is not allowed to use the page_pool_alloc() API this way
(from a work-queue).  The PP alloc-side API must only be used under NAPI
protection.  Thanks for spotting this Sebastian!

Will/can any of the Cc'ed Marvell people work on a fix?

--Jesper