From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Subject: Re: [PATCH net] ixgbe: check return value of napi_complete_done()
Date: Thu, 20 Sep 2018 14:01:37 -0700
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References: <20180920190113.490005-1-songliubraving@fb.com>
         <c1251d5d-4b18-a1de-acd2-6de829b7c7ac@gmail.com>
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Cc: intel-wired-lan@lists.osuosl.org, kernel-team@fb.com,
        stable@vger.kernel.org
To: Eric Dumazet <eric.dumazet@gmail.com>,
        Song Liu <songliubraving@fb.com>, netdev@vger.kernel.org
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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.
> >=20
> > Cc: stable@vger.kernel.org # 4.10+
> > Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
> > Suggested-by: Eric Dumazet <edumazet@google.com>
> > Signed-off-by: Song Liu <songliubraving@fb.com>
> > ---
>=20
>=20
> Well, unfortunately we do not know why this is needed,
> this is why I have not yet sent this patch formally.
>=20
> netpoll has correct synchronization :
>=20
> poll_napi() places into napi->poll_owner current cpu number before
> calling poll_one_napi()
>=20
> netpoll_poll_lock() does also use napi->poll_owner
>=20
> When netpoll calls ixgbe poll() method, it passed a budget of 0,
> meaning napi_complete_done() is not called.
>=20
> 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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