On Tue, Nov 29, 2016 at 5:20 PM, Michael S. Tsirkin <m...@redhat.com> wrote:
> On Tue, Nov 29, 2016 at 04:25:36PM +0100, Andrey Konovalov wrote:
>> This patch changes tun.c to call netif_receive_skb instead of netif_rx
>> when a packet is received. The difference between the two is that netif_rx
>> queues the packet into the backlog, and netif_receive_skb proccesses the
>> packet in the current context.
>> This patch is required for syzkaller  to collect coverage from packet
>> receive paths, when a packet being received through tun (syzkaller collects
>> coverage per process in the process context).
>> A similar patch was introduced back in 2010 [2, 3], but the author found
>> out that the patch doesn't help with the task he had in mind (for cgroups
>> to shape network traffic based on the original process) and decided not to
>> go further with it. The main concern back then was about possible stack
>> exhaustion with 4K stacks, but CONFIG_4KSTACKS was removed and stacks are
>> 8K now.
>>  https://github.com/google/syzkaller
>>  https://www.spinics.net/lists/netdev/thrd440.html#130570
>>  https://www.spinics.net/lists/netdev/msg130570.html
>> Signed-off-by: Andrey Konovalov <andreyk...@google.com>
> This was on my list of things to investigate ever since
> 8k stack default went in. Thanks for looking into this!
> I note that there are still seem to exit 3 architectures that do have
Missed that, mailed v2.
> How about a wrapper that does netif_rx_ni with CONFIG_4KSTACKS.
>> drivers/net/tun.c | 4 +++-
>> 1 file changed, 3 insertions(+), 1 deletion(-)
>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>> index 8093e39..4b56e91 100644
>> --- a/drivers/net/tun.c
>> +++ b/drivers/net/tun.c
>> @@ -1304,7 +1304,9 @@ static ssize_t tun_get_user(struct tun_struct *tun,
>> struct tun_file *tfile,
>> skb_probe_transport_header(skb, 0);
>> rxhash = skb_get_hash(skb);
>> - netif_rx_ni(skb);
>> + local_bh_disable();
>> + netif_receive_skb(skb);
>> + local_bh_enable();
>> stats = get_cpu_ptr(tun->pcpu_stats);
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