netdev - Re: [PATCH] ptr_ring: add barriers

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Message-ID: <93ed1559-74d4-d72f-0969-12bfaf370cc1@caviumnetworks.com>
Date:   Tue, 12 Dec 2017 11:58:52 +0530
From:   George Cherian <gcherian@...iumnetworks.com>
To:     David Miller <davem@...emloft.net>, mst@...hat.com
Cc:     linux-kernel@...r.kernel.org, george.cherian@...ium.com,
        jasowang@...hat.com, edumazet@...gle.com, netdev@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] ptr_ring: add barriers

Hi David,

On 12/11/2017 09:23 PM, David Miller wrote:
> From: "Michael S. Tsirkin" <mst@...hat.com>
> Date: Tue, 5 Dec 2017 21:29:37 +0200
> 
>> Users of ptr_ring expect that it's safe to give the
>> data structure a pointer and have it be available
>> to consumers, but that actually requires an smb_wmb
>> or a stronger barrier.
>>
>> In absence of such barriers and on architectures that reorder writes,
>> consumer might read an un=initialized value from an skb pointer stored
>> in the skb array.  This was observed causing crashes.
>>
>> To fix, add memory barriers.  The barrier we use is a wmb, the
>> assumption being that producers do not need to read the value so we do
>> not need to order these reads.
>>
>> Reported-by: George Cherian <george.cherian@...ium.com>
>> Suggested-by: Jason Wang <jasowang@...hat.com>
>> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> 
> I'm asked for asking for testing feedback and did not get it in a
> reasonable amount of time.
> 
The tests have completed more than 48 hours without any failures.
I won't interrupt the same and run for longer time.
In case of any issue I will report the same.
> So I'm applying this as-is, and queueing it up for -stable.
> 
> Thank you.

Regards,
-George
>