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Date:   Mon, 13 Mar 2017 06:18:04 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Petr Vorel <petr.vorel@...il.com>
Cc:     netdev@...r.kernel.org, hayeswang@...ltek.com, davem@...emloft.net
Subject: Re: [PATCH 1/1] r8152: fix NULL pointer dereference in r8152_poll

On Mon, 2017-03-13 at 13:47 +0100, Petr Vorel wrote:
> commit 7489bdadb7d1 (r8152: check rx after napi is enabled) causes null
> pointer dereference when using device as under root:
> 
>  # rmmod r8152 # or lsusb -v
> NOHZ: local_softirq_pending 08
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
> IP: r8152_poll+0x125/0x570 [r8152]
> PGD 89b4cf067
> PUD 898ff2067
> PMD 0
> Oops: 0002 [#1] PREEMPT SMP
> 
> Signed-off-by: Petr Vorel <petr.vorel@...il.com>
> ---
> NOTE: This is just a workaround, I suppose, there is better way how to fix that
> (which allows keeping scheduling the napi for rx after napi_enable()).
> ---
>  drivers/net/usb/r8152.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/net/usb/r8152.c b/drivers/net/usb/r8152.c
> index 986243c932cc..79c665a89a47 100644
> --- a/drivers/net/usb/r8152.c
> +++ b/drivers/net/usb/r8152.c
> @@ -3703,8 +3703,6 @@ static int rtl8152_resume(struct usb_interface *intf)
>  			napi_enable(&tp->napi);
>  			clear_bit(SELECTIVE_SUSPEND, &tp->flags);
>  			smp_mb__after_atomic();
> -			if (!list_empty(&tp->rx_done))
> -				napi_schedule(&tp->napi);
>  		} else {
>  			tp->rtl_ops.up(tp);
>  			netif_carrier_off(tp->netdev);


The proper work around is to enclose the napi_schedule() in a
local_bh_enable()/local_bh_disable()  pair.



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