linux-kernel - Re: [net v1] net: wwan: t7xx: Fix napi rx poll issue

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Message-ID: <20250520153942.7cb63bac@kernel.org>
Date: Tue, 20 May 2025 15:39:42 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Jinjian Song <jinjian.song@...ocom.com>
Cc: andrew+netdev@...n.ch, angelogioacchino.delregno@...labora.com,
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Subject: Re: [net v1] net: wwan: t7xx: Fix napi rx poll issue

On Tue, 20 May 2025 15:05:34 +0800 Jinjian Song wrote:
> >Synchronization is about ensuring that the condition validating
> >by the if() remains true for as long as necessary.
> >You need to wrap the read with READ_ONCE() and write with WRITE_ONCE().
> >The rest if fine because netdev unregister sync against NAPIs in flight.
> >  
> 
> Hi Jakub,
>   I think I got your point.
>   I can use the atomic_t usage in struct t7xx_ccmni to synchronization.
>   
>   static void t7xx_ccmni_wwan_dellink(...) {
> 
>   [...]
> 
>   if (WARN_ON(ctlb->ccmni_inst[if_id] != ccmni))
>     return;
> 
>   unregister_netdevice(dev);
> 
>   //Add here use this variable(ccmnii->usage) to synchronization
> 
>   if (atomic_read(&ccmni->usage) == 0)
>      ccmni == NULL;
> 
>   }
> 
>   How about this modify?

Just use READ_ONCE() / WRITE_ONCE() on the pointer as I suggested.