linux-kernel - Re: [PATCH net v3 2/2] net: ethernet: oa_tc6: fix tx skb race condition between reference pointers

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Message-ID: <20241213184253.7c8203ce@kernel.org>
Date: Fri, 13 Dec 2024 18:42:53 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: <Parthiban.Veerasooran@...rochip.com>
Cc: <andrew+netdev@...n.ch>, <davem@...emloft.net>, <edumazet@...gle.com>,
 <pabeni@...hat.com>, <netdev@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <UNGLinuxDriver@...rochip.com>,
 <jacob.e.keller@...el.com>
Subject: Re: [PATCH net v3 2/2] net: ethernet: oa_tc6: fix tx skb race
 condition between reference pointers

On Fri, 13 Dec 2024 10:35:03 +0000 Parthiban.Veerasooran@...rochip.com
wrote:
> >> start_xmit runs in BH / softirq context. You can't take sleeping locks.
> >> The lock has to be a spin lock. You could possibly try to use the
> >> existing spin lock of the tx queue (__netif_tx_lock()) but that may be
> >> more challenging to do cleanly from within a library..  
> > Thanks for the input. Yes, it looks like implementing a spin lock would
> > be a right choice. I will implement it and do the testing as you
> > suggested below and share the feedback.  
> I tried using spin_lock_bh() variants (as the softirq involved) on both 
> start_xmit() and spi_thread() where the critical regions need to be 
> protected and tested by enabling the Kconfigs in the 
> kernel/configs/debug.config. Didn't notice any warnings in the dmesg log.
> 
> Note: Prior to the above test, purposefully I tried with spin_lock() 
> variants on both the sides to check/simulate for the warnings using 
> Kconfigs kernel/configs/debug.config. Got some warnings in the dmesg 
> regarding deadlock which clarified the expected behavior. And then I 
> proceeded with the above fix and it worked as expected.
> 
> If you agree, I will prepare the next version with this fix and post.

Go ahead.