netdev - Re: [PATCH net] ixgbe: check return value of napi_complete

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Message-ID: <2ca0e823642d232092017f66e8151652e22e74a1.camel@intel.com>
Date:   Thu, 20 Sep 2018 14:01:37 -0700
From:   Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        Song Liu <songliubraving@...com>, netdev@...r.kernel.org
Cc:     intel-wired-lan@...ts.osuosl.org, kernel-team@...com,
        stable@...r.kernel.org
Subject: Re: [PATCH net] ixgbe: check return value of napi_complete_done()

On Thu, 2018-09-20 at 13:35 -0700, Eric Dumazet wrote:
> On 09/20/2018 12:01 PM, Song Liu wrote:
> > The NIC driver should only enable interrupts when napi_complete_done()
> > returns true. This patch adds the check for ixgbe.
> > 
> > Cc: stable@...r.kernel.org # 4.10+
> > Cc: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
> > Suggested-by: Eric Dumazet <edumazet@...gle.com>
> > Signed-off-by: Song Liu <songliubraving@...com>
> > ---
> 
> 
> Well, unfortunately we do not know why this is needed,
> this is why I have not yet sent this patch formally.
> 
> netpoll has correct synchronization :
> 
> poll_napi() places into napi->poll_owner current cpu number before
> calling poll_one_napi()
> 
> netpoll_poll_lock() does also use napi->poll_owner
> 
> When netpoll calls ixgbe poll() method, it passed a budget of 0,
> meaning napi_complete_done() is not called.
> 
> As long as we can not explain the problem properly in the changelog,
> we should investigate, otherwise we will probably see coming dozens of
> patches
> trying to fix a 'potential hazard'.

Agreed, which is why I have our validation and developers looking into it,
while we test the current patch from Song.

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