netdev - Re: [PATCH net 1/3] igc: Clean the TX buffer and TX descriptor ring

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Message-ID: <ZF5bkhhs+Ue+DZfG@boxer>
Date: Fri, 12 May 2023 17:30:26 +0200
From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To: "Zulkifli, Muhammad Husaini" <muhammad.husaini.zulkifli@...el.com>
CC: Jakub Kicinski <kuba@...nel.org>, "Nguyen, Anthony L"
	<anthony.l.nguyen@...el.com>, "davem@...emloft.net" <davem@...emloft.net>,
	"pabeni@...hat.com" <pabeni@...hat.com>, "edumazet@...gle.com"
	<edumazet@...gle.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"Neftin, Sasha" <sasha.neftin@...el.com>, Naama Meir
	<naamax.meir@...ux.intel.com>
Subject: Re: [PATCH net 1/3] igc: Clean the TX buffer and TX descriptor ring

On Fri, May 12, 2023 at 08:51:23AM +0000, Zulkifli, Muhammad Husaini wrote:
> Hi Jakub,
> 
> > On Tue,  9 May 2023 10:09:33 -0700 Tony Nguyen wrote:
> > > There could be a race condition during link down where interrupt being
> > > generated and igc_clean_tx_irq() been called to perform the TX
> > > completion. Properly clear the TX buffer and TX descriptor ring to
> > > avoid those case.
> > 
> > > +	/* Zero out the buffer ring */
> > > +	memset(tx_ring->tx_buffer_info, 0,
> > > +	       sizeof(*tx_ring->tx_buffer_info) * tx_ring->count);
> > > +
> > > +	/* Zero out the descriptor ring */
> > > +	memset(tx_ring->desc, 0, tx_ring->size);
> > 
> > Just from the diff and the commit description this does not seem obviously
> > correct. Race condition means the two functions can run at the same time,
> > and memset() is not atomic.
> 
> While a link is going up or down and a lot of packets(UDP) are being sent transmitted, 
> we are observing some kernel panic issues. On my side, it was easily to reproduce.
> It's possible that igc_clean_tx_irq() was called to complete the TX during link up/down 
> based on how the call trace looks. With this fix, I not observed the issue anymore.

then include the splat you were getting in the commit msg as well as steps
to repro.

from a brief look it looks like ndo_stop() path does not disable Tx rings
before cleaning them? This is being done when configuring xsk_pool on a
given Tx ring, though.

> 
> Almost similar issue reported before in here:
> https://lore.kernel.org/all/SJ1PR11MB6180CDB866753CFBC2F9AF75B8959@SJ1PR11MB6180.namprd11.prod.outlook.com/
> 
> > --
> > pw-bot: cr
>