netdev - Re: [PATCH net] net/mlx4_en: fixup xdp tx irq to match rx

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Date:   Fri, 14 Oct 2016 11:14:21 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     bblanco@...mgrid.com
Cc:     netdev@...r.kernel.org, alexei.starovoitov@...il.com,
        ttoukan.linux@...il.com, gerlitz.or@...il.com,
        saeedm@....mellanox.co.il, brouer@...hat.com
Subject: Re: [PATCH net] net/mlx4_en: fixup xdp tx irq to match rx

From: Brenden Blanco <bblanco@...mgrid.com>
Date: Thu, 13 Oct 2016 13:13:11 -0700

> In cases where the number of tx rings is not a multiple of the number of
> rx rings, the tx completion event will be handled on a different core
> from the transmit and population of the ring. Races on the ring will
> lead to a double-free of the page, and possibly other corruption.
> 
> The rings are initialized by default with a valid multiple of rings,
> based on the number of cpus, therefore an invalid configuration requires
> ethtool to change the ring layout. For instance 'ethtool -L eth0 rx 9 tx
> 8' will cause packets received on rx0, and XDP_TX'd to tx48, to be
> completed on cpu3 (48 % 9 == 3).
> 
> Resolve this discrepancy by shifting the irq for the xdp tx queues to
> start again from 0, modulo rx_ring_num.
> 
> Fixes: 9ecc2d86171a ("net/mlx4_en: add xdp forwarding and data write support")
> Reported-by: Jesper Dangaard Brouer <brouer@...hat.com>
> Signed-off-by: Brenden Blanco <bblanco@...mgrid.com>

Applied and queued up for -stable, thanks.