linux-kernel - Re: [PATCH] tg3: driver sleeps indefinitely when EEH errors exceed eeh_max

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Date:   Mon, 15 Jun 2020 18:33:29 -0700
From:   Michael Chan <michael.chan@...adcom.com>
To:     David Christensen <drc@...ux.vnet.ibm.com>
Cc:     Netdev <netdev@...r.kernel.org>,
        Siva Reddy Kallam <siva.kallam@...adcom.com>,
        Prashant Sreedharan <prashant@...adcom.com>,
        Michael Chan <mchan@...adcom.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tg3: driver sleeps indefinitely when EEH errors exceed eeh_max_freezes

On Mon, Jun 15, 2020 at 3:21 PM David Christensen
<drc@...ux.vnet.ibm.com> wrote:
>
> On 6/15/20 1:45 PM, Michael Chan wrote:
> > On Mon, Jun 15, 2020 at 12:01 PM David Christensen
> > <drc@...ux.vnet.ibm.com> wrote:
> >>
> >> The driver function tg3_io_error_detected() calls napi_disable twice,
> >> without an intervening napi_enable, when the number of EEH errors exceeds
> >> eeh_max_freezes, resulting in an indefinite sleep while holding rtnl_lock.
> >>
> >> The function is called once with the PCI state pci_channel_io_frozen and
> >> then called again with the state pci_channel_io_perm_failure when the
> >> number of EEH failures in an hour exceeds eeh_max_freezes.
> >>
> >> Protecting the calls to napi_enable/napi_disable with a new state
> >> variable prevents the long sleep.
> >
> > This works, but I think a simpler fix is to check tp->pcierr_recovery
> > in tg3_io_error_detected() and skip most of the tg3 calls (including
> > the one that disables NAPI) if the flag is true.
>
> This might be the smallest change that would work.  Does it make sense
> to the reader?
>
> diff --git a/drivers/net/ethernet/broadcom/tg3.c
> b/drivers/net/ethernet/broadcom/tg3.c
> index 7a3b22b35238..1f37c69d213d 100644
> --- a/drivers/net/ethernet/broadcom/tg3.c
> +++ b/drivers/net/ethernet/broadcom/tg3.c
> @@ -18168,8 +18168,8 @@ static pci_ers_result_t
> tg3_io_error_detected(struct pci_dev *pdev,
>
>          rtnl_lock();
>
> -       /* We probably don't have netdev yet */
> -       if (!netdev || !netif_running(netdev))
> +       /* May be second call or maybe we don't have netdev yet */
> +       if (tp->pcierr_recovery || !netdev || !netif_running(netdev))

Dereferencing tp needs to be done after checking netdev.  If we don't
have netdev, tp won't be valid.

Other than that, I think the logic looks good and is quite clear.

Thanks.