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From: Nicolas Ferre <nicolas.ferre@atmel.com>
To: David Miller <davem@davemloft.net>
Cc: <netdev@vger.kernel.org>, <linux-arm-kernel@lists.infradead.org>,
	<havard@skinnemoen.net>, <plagnioj@jcrosoft.com>,
	<jamie@jamieiles.com>, <linux-kernel@vger.kernel.org>,
	<patrice.vilchez@atmel.com>
Subject: Re: [PATCH 04/10] net/macb: Fix a race in macb_start_xmit()
Date: Thu, 6 Sep 2012 16:52:45 +0200	[thread overview]
Message-ID: <5048B8BD.3000804@atmel.com> (raw)
In-Reply-To: <20120905.173023.2235590074897156746.davem@davemloft.net>

On 09/05/2012 11:30 PM, David Miller :
> From: Nicolas Ferre <nicolas.ferre@atmel.com>
> Date: Wed, 5 Sep 2012 10:19:11 +0200
> 
>> From: Havard Skinnemoen <havard@skinnemoen.net>
>>
>> Fix a race in macb_start_xmit() where we unconditionally set the TSTART bit.
>> If an underrun just happened (we do this with interrupts disabled, so it might
>> not have been handled yet), the controller starts transmitting from the first
>> entry in the ring, which is usually wrong.
>> Restart the controller after error handling.
>>
>> Signed-off-by: Havard Skinnemoen <havard@skinnemoen.net>
>> [nicolas.ferre@atmel.com: split patch in topics]
>> Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
> 
> Accumulating special case code and checks into the hot path of TX packet
> processing is extremely unwise.
> 
> Instead, when you handle the TX error conditions and reset the chip you
> should first ensure that there are no flows of control in the transmit
> function of your driver by using the appropriate locking et al. facilities.
> 
> For example, you can quiesce the transmit path by handling the chip error
> interrupt as follows:
> 
> 1) Disable chip interrupt generation.
> 
> 2) Schedule a workqueue so you can process the reset outside of hard
>    interrupt context.
> 
> 3) In the workqueue function, disable NAPI and perform a
>    netif_tx_disable() to guarentee there are no threads of
>    execution trying to queue up packets for TX into the driver.
> 
> 4) Perform your chip reset and whatever else is necessary.
> 
> 5) Re-enable NAPI and TX.
> 
> Then you don't need any special checks in your xmit method at all.

I see... I will rework the series and try to implement this as part of
the "[PATCH 06/10] net/macb: better manage tx errors"

So this patch will disappear in future v2 series and patch 06 will be
seriously modified. In fact I will also try to stack "cosmetic" patches
at the beginning of the series.

Thanks, best regards,
-- 
Nicolas Ferre

  reply	other threads:[~2012-09-06 14:52 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-09-05  8:19 [PATCH 00/10] net/macb: driver enhancement concerning GEM support, ring logic and cleanup Nicolas Ferre
2012-09-05  8:19 ` [PATCH 01/10] net/macb: Add support for Gigabit Ethernet mode Nicolas Ferre
2012-09-05  8:19 ` [PATCH 02/10] net/macb: memory barriers cleanup Nicolas Ferre
2012-09-05  8:19 ` [PATCH 03/10] net/macb: change debugging messages Nicolas Ferre
2012-09-05  8:19 ` [PATCH 04/10] net/macb: Fix a race in macb_start_xmit() Nicolas Ferre
2012-09-05 21:30   ` David Miller
2012-09-06 14:52     ` Nicolas Ferre [this message]
2012-09-06 15:49     ` Havard Skinnemoen
2012-09-07 16:34       ` Nicolas Ferre
2012-09-05  9:00 ` [PATCH 05/10] net/macb: clean up ring buffer logic Nicolas Ferre
2012-09-05  9:00 ` [PATCH 06/10] net/macb: better manage tx errors Nicolas Ferre
2012-09-05  9:00 ` [PATCH 07/10] net/macb: tx status is more than 8 bits now Nicolas Ferre
2012-09-05  9:00 ` [PATCH 08/10] net/macb: macb_get_drvinfo: add GEM/MACB suffix to differentiate revision Nicolas Ferre
2012-09-05 21:31   ` David Miller
2012-09-05 23:27   ` Ben Hutchings
2012-09-06 14:01     ` Nicolas Ferre
2012-09-06 17:42       ` David Miller
2012-09-05  9:00 ` [PATCH 09/10] net/macb: ethtool interface: add register dump feature Nicolas Ferre
2012-09-05 21:32   ` David Miller
2012-09-05 23:36   ` Ben Hutchings
2012-09-06 14:20     ` [PATCH v2 " Nicolas Ferre
2012-09-06 14:34       ` Ben Hutchings
2012-09-05  9:04 ` [PATCH 10/10] net/macb: Offset first RX buffer by two bytes Nicolas Ferre

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