linux-kernel - Re: [PATCH net-next v3 4/9] net: stmmac: Introduce dwmac1000 ptp_clock

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Message-ID: <20241112115009.028b8724@fedora.home>
Date: Tue, 12 Nov 2024 11:50:09 +0100
From: Maxime Chevallier <maxime.chevallier@...tlin.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: Jakub Kicinski <kuba@...nel.org>, Alexandre Torgue
 <alexandre.torgue@...s.st.com>, Jose Abreu <joabreu@...opsys.com>, Andrew
 Lunn <andrew+netdev@...n.ch>, davem@...emloft.net, Eric Dumazet
 <edumazet@...gle.com>, Maxime Coquelin <mcoquelin.stm32@...il.com>, Richard
 Cochran <richardcochran@...il.com>, Alexis Lothoré
 <alexis.lothore@...tlin.com>, Thomas Petazzoni
 <thomas.petazzoni@...tlin.com>, netdev@...r.kernel.org,
 linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v3 4/9] net: stmmac: Introduce dwmac1000
 ptp_clock_info and operations

Hello Jakub, Paolo,

On Tue, 12 Nov 2024 10:28:21 +0100
Paolo Abeni <pabeni@...hat.com> wrote:

> On 11/12/24 01:12, Jakub Kicinski wrote:
> > On Wed,  6 Nov 2024 10:03:25 +0100 Maxime Chevallier wrote:  
> >> +		mutex_unlock(&priv->aux_ts_lock);
> >> +
> >> +		/* wait for auxts fifo clear to finish */
> >> +		ret = readl_poll_timeout(ptpaddr + PTP_TCR, tcr_val,
> >> +					 !(tcr_val & GMAC_PTP_TCR_ATSFC),
> >> +					 10, 10000);  
> > 
> > Is there a good reason to wait for the flush to complete outside of 
> > the mutex?   
> 
> Indeed looking at other `ptpaddr` access use-case, it looks like the
> mutex protects both read and write accesses.
> 
> @Maxime: is the above intentional? looks race-prone

You're right, this is racy... It wasn't intentionnal, it's actually the
same logic as dwmac4 uses so looks like dwmac4 is also incorrect in
that regard.

I'll send a v4 with that change, and a fix for dwmac4 along the way
then.

Thanks for spotting this,

Maxime