netdev - Re: [Xen-devel] [PATCHv2 net-next] xen-netback: fix race between napi

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Date:	Fri, 16 May 2014 10:58:53 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	David Vrabel <david.vrabel@...rix.com>
CC:	<netdev@...r.kernel.org>, Wei Liu <wei.liu2@...rix.com>,
	<xen-devel@...ts.xenproject.org>
Subject: Re: [Xen-devel] [PATCHv2 net-next] xen-netback: fix race between
 napi_complete() and interrupt handler

On Fri, 2014-05-16 at 10:53 +0100, David Vrabel wrote:
> On 16/05/14 09:30, Ian Campbell wrote:
> > On Thu, 2014-05-15 at 18:17 +0100, David Vrabel wrote:
> >> When the NAPI budget was not all used, xenvif_poll() would call
> >> napi_complete() /after/ enabling the interrupt.  This resulted in a
> >> race between the napi_complete() and the napi_schedule() in the
> >> interrupt handler.  The use of local_irq_save/restore() avoided by
> >> race iff the handler is running on the same CPU but not if it was
> >> running on a different CPU.
> >>
> >> Fix this properly by calling napi_complete() before reenabling
> >> interrupts (in the xenvif_napi_schedule_or_enable_irq() call).
> >>
> >> Signed-off-by: David Vrabel <david.vrabel@...rix.com>
> >> ---
> >> v2:
> >> - Rename xenvif_check_rx_xenvif() to
> >>   xenvif_napi_schedule_or_enable_irq() to make it more obvious what it
> >>   does.
> > 
> > Which is to update the event pointer such that IRQs are generated again
> > rather than enabling IRQs as such (enable_irq makes me think of
> > EFLAGS.IF). But given that I can't think of a better way to describe it:
> > Acked-by: Ian Campbell <ian.campbell@...rix.com>
> 
> Would xenvif_napi_schedule_or_enable_event() be better?

I think so, yes. (_events?)

Ian.

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