netdev - Re: [PATCH net-next] bnx2x: avoid soft lockup in bnx2x

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Message-Id: <20151208.225527.75074006409045414.davem@davemloft.net>
Date:	Tue, 08 Dec 2015 22:55:27 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, ariel.elior@...gic.com, willemb@...gle.com
Subject: Re: [PATCH net-next] bnx2x: avoid soft lockup in bnx2x_poll()

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Tue, 08 Dec 2015 05:54:40 -0800

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Under heavy TX load, bnx2x_poll() can loop forever and trigger
> soft lockup bugs.
> 
> A napi poll handler must yield after one TX completion round,
> risk of livelock is too high otherwise.
> 
> Bug is very easy to trigger using a debug build, and udp flood, because
> of added cpu cycles in TX completion, and we do not receive enough
> packets to break the loop.
> 
> Reported-by: Willem de Bruijn <willemb@...gle.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Indeed, no driver should ever do more than one TX completion round
per NAPI poll call, _ever_.
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