netdev - Re: [PATCH 1/1] net: macb: fix the RX queue reset in macb

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Message-Id: <20161127.202549.1887792653016840262.davem@davemloft.net>
Date:   Sun, 27 Nov 2016 20:25:49 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     cyrille.pitchen@...el.com
Cc:     nicolas.ferre@...el.com, netdev@...r.kernel.org,
        soren.brinkmann@...inx.com, Andrei.Pistirica@...rochip.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] net: macb: fix the RX queue reset in macb_rx()

From: Cyrille Pitchen <cyrille.pitchen@...el.com>
Date: Fri, 25 Nov 2016 09:49:32 +0100

> On macb only (not gem), when a RX queue corruption was detected from
> macb_rx(), the RX queue was reset: during this process the RX ring
> buffer descriptor was initialized by macb_init_rx_ring() but we forgot
> to also set bp->rx_tail to 0.
> 
> Indeed, when processing the received frames, bp->rx_tail provides the
> macb driver with the index in the RX ring buffer of the next buffer to
> process. So when the whole ring buffer is reset we must also reset
> bp->rx_tail so the driver is synchronized again with the hardware.
> 
> Since macb_init_rx_ring() is called from many locations, currently from
> macb_rx() and macb_init_rings(), we'd rather add the "bp->rx_tail = 0;"
> line inside macb_init_rx_ring() than add the very same line after each
> call of this function.
> 
> Without this fix, the rx queue is not reset properly to recover from
> queue corruption and connection drop may occur.
> 
> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@...el.com>
> Fixes: 9ba723b081a2 ("net: macb: remove BUG_ON() and reset the queue to handle RX errors")

This doesn't apply cleanly to the 'net' tree, where
RX_RING_SIZE is used instead of bp->rx_ring_size. It seems
you generated this against net-next, however you didn't say
that either in your Subject line nor the commit message.

As a bug fix this should be targetted at 'net'.