Re: [BUG] 4.10-rc8 - ping spinning?

2017-02-16 Thread Soheil Hassas Yeganeh 
On Thu, Feb 16, 2017 at 11:08 AM,   wrote:
> On Thu, Feb 16, 2017 at 10:52:19AM -0500, Soheil Hassas Yeganeh wrote:
>> On Thu, Feb 16, 2017 at 10:50 AM, Soheil Hassas Yeganeh
>>  wrote:
>> > Thank you Vito for the report.
>> >
>> > The patch you cited actually resolves a similar backward compatibility
>> > problem for traceroute.
>> >
>> > I suspect the problem here is that there's a local error queued on the
>> > error queue after an ICMP message. ping apparently expect the
>> > sk->sk_err to be set for the local errors as well, and hence the
>> > error. Ideally, ping should read the error queue if there an EPOLLERR,
>> > because local errors never sk->sk_err on their own. That is, if we
>> > have
>>
>> [oops] That is, if we have only one local error on the error queue, we
>> cannot rely on having an error on recvmsg (i.e., sk->sk_err being set)
>> even in 4.9.
>>
>> 
>
> Hi Soheil,
>
> This doesn't appear to be trivially reproducible here by just running ping
> as it were originally discovered.  I'll see if I can reliably cause the
> malfunction somehow, but until then I can't meaningfully test patches.
>
> Perhaps a form of fault injection would make more sense if there's a
> reasonable idea of what this is stemming from?

I tried to generate different ICMP errors as well as local errors, but
unfortunately haven't been able to reproduce the problem.

> I've opened an issue with iputils on github in the event that this is found
> to be a ping bug.  Your input might be helpful there as well:
> https://github.com/iputils/iputils/issues/74

Sent a pull request. Although, we might want to at least confirm the
userspace patch fixes the issue in ping.

Thanks!
Soheil

> Thanks,
> Vito Caputo

Re: [BUG] 4.10-rc8 - ping spinning?

2017-02-16 Thread Soheil Hassas Yeganeh 
On Thu, Feb 16, 2017 at 11:08 AM,   wrote:
> On Thu, Feb 16, 2017 at 10:52:19AM -0500, Soheil Hassas Yeganeh wrote:
>> On Thu, Feb 16, 2017 at 10:50 AM, Soheil Hassas Yeganeh
>>  wrote:
>> > Thank you Vito for the report.
>> >
>> > The patch you cited actually resolves a similar backward compatibility
>> > problem for traceroute.
>> >
>> > I suspect the problem here is that there's a local error queued on the
>> > error queue after an ICMP message. ping apparently expect the
>> > sk->sk_err to be set for the local errors as well, and hence the
>> > error. Ideally, ping should read the error queue if there an EPOLLERR,
>> > because local errors never sk->sk_err on their own. That is, if we
>> > have
>>
>> [oops] That is, if we have only one local error on the error queue, we
>> cannot rely on having an error on recvmsg (i.e., sk->sk_err being set)
>> even in 4.9.
>>
>> 
>
> Hi Soheil,
>
> This doesn't appear to be trivially reproducible here by just running ping
> as it were originally discovered.  I'll see if I can reliably cause the
> malfunction somehow, but until then I can't meaningfully test patches.
>
> Perhaps a form of fault injection would make more sense if there's a
> reasonable idea of what this is stemming from?

I tried to generate different ICMP errors as well as local errors, but
unfortunately haven't been able to reproduce the problem.

> I've opened an issue with iputils on github in the event that this is found
> to be a ping bug.  Your input might be helpful there as well:
> https://github.com/iputils/iputils/issues/74

Sent a pull request. Although, we might want to at least confirm the
userspace patch fixes the issue in ping.

Thanks!
Soheil

> Thanks,
> Vito Caputo

Re: [BUG] 4.10-rc8 - ping spinning?

2017-02-16 Thread lkml 
On Thu, Feb 16, 2017 at 10:52:19AM -0500, Soheil Hassas Yeganeh wrote:
> On Thu, Feb 16, 2017 at 10:50 AM, Soheil Hassas Yeganeh
>  wrote:
> > Thank you Vito for the report.
> >
> > The patch you cited actually resolves a similar backward compatibility
> > problem for traceroute.
> >
> > I suspect the problem here is that there's a local error queued on the
> > error queue after an ICMP message. ping apparently expect the
> > sk->sk_err to be set for the local errors as well, and hence the
> > error. Ideally, ping should read the error queue if there an EPOLLERR,
> > because local errors never sk->sk_err on their own. That is, if we
> > have
> 
> [oops] That is, if we have only one local error on the error queue, we
> cannot rely on having an error on recvmsg (i.e., sk->sk_err being set)
> even in 4.9.
> 
> 

Hi Soheil,

This doesn't appear to be trivially reproducible here by just running ping
as it were originally discovered.  I'll see if I can reliably cause the
malfunction somehow, but until then I can't meaningfully test patches.

Perhaps a form of fault injection would make more sense if there's a
reasonable idea of what this is stemming from?

I've opened an issue with iputils on github in the event that this is found
to be a ping bug.  Your input might be helpful there as well:
https://github.com/iputils/iputils/issues/74

Thanks,
Vito Caputo

Re: [BUG] 4.10-rc8 - ping spinning?

2017-02-16 Thread lkml 
On Thu, Feb 16, 2017 at 10:52:19AM -0500, Soheil Hassas Yeganeh wrote:
> On Thu, Feb 16, 2017 at 10:50 AM, Soheil Hassas Yeganeh
>  wrote:
> > Thank you Vito for the report.
> >
> > The patch you cited actually resolves a similar backward compatibility
> > problem for traceroute.
> >
> > I suspect the problem here is that there's a local error queued on the
> > error queue after an ICMP message. ping apparently expect the
> > sk->sk_err to be set for the local errors as well, and hence the
> > error. Ideally, ping should read the error queue if there an EPOLLERR,
> > because local errors never sk->sk_err on their own. That is, if we
> > have
> 
> [oops] That is, if we have only one local error on the error queue, we
> cannot rely on having an error on recvmsg (i.e., sk->sk_err being set)
> even in 4.9.
> 
> 

Hi Soheil,

This doesn't appear to be trivially reproducible here by just running ping
as it were originally discovered.  I'll see if I can reliably cause the
malfunction somehow, but until then I can't meaningfully test patches.

Perhaps a form of fault injection would make more sense if there's a
reasonable idea of what this is stemming from?

I've opened an issue with iputils on github in the event that this is found
to be a ping bug.  Your input might be helpful there as well:
https://github.com/iputils/iputils/issues/74

Thanks,
Vito Caputo

Re: [BUG] 4.10-rc8 - ping spinning?

2017-02-16 Thread Soheil Hassas Yeganeh 
On Thu, Feb 16, 2017 at 10:50 AM, Soheil Hassas Yeganeh
<soh...@google.com> wrote:
> Thank you Vito for the report.
>
> The patch you cited actually resolves a similar backward compatibility
> problem for traceroute.
>
> I suspect the problem here is that there's a local error queued on the
> error queue after an ICMP message. ping apparently expect the
> sk->sk_err to be set for the local errors as well, and hence the
> error. Ideally, ping should read the error queue if there an EPOLLERR,
> because local errors never sk->sk_err on their own. That is, if we
> have

[oops] That is, if we have only one local error on the error queue, we
cannot rely on having an error on recvmsg (i.e., sk->sk_err being set)
even in 4.9.

Thanks,
Soheil

> But as a workaround, would you mind trying the following patch to see
> if it resolves the issue reported?
>
> From: Soheil Hassas Yeganeh <soh...@google.com>
> Date: Thu, 16 Feb 2017 10:48:24 -0500
> ---
>  net/core/skbuff.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 734c71468b01..2b774b564024 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -3717,7 +3717,8 @@ EXPORT_SYMBOL(sock_queue_err_skb);
>  static bool is_icmp_err_skb(const struct sk_buff *skb)
>  {
>   return skb && (SKB_EXT_ERR(skb)->ee.ee_origin == SO_EE_ORIGIN_ICMP ||
> -   SKB_EXT_ERR(skb)->ee.ee_origin == SO_EE_ORIGIN_ICMP6);
> +   SKB_EXT_ERR(skb)->ee.ee_origin == SO_EE_ORIGIN_ICMP6 ||
> +   SKB_EXT_ERR(skb)->ee.ee_origin == SO_EE_ORIGIN_LOCAL);
>  }
>
>  struct sk_buff *sock_dequeue_err_skb(struct sock *sk)
> --
>
> Thanks!
> Soheil
>
> On Thu, Feb 16, 2017 at 7:05 AM,  <l...@pengaru.com> wrote:
>> Hello netdev,
>>
>> Please see the forwarded message below.  This was sent to linux-kernel but
>> after digging a little I suspect it's specific to the network stack.
>>
>> Perusing the net/ changes between 4.9 and 4.10-rc8 this sounded awful related
>> to what I'm observing:
>>
>> commit 83a1a1a70e87f676fbb6086b26b6ac7f7fdd107d
>> Author: Soheil Hassas Yeganeh <soh...@google.com>
>> Date:   Wed Nov 30 14:01:08 2016 -0500
>>
>> sock: reset sk_err for ICMP packets read from error queue
>>
>> Only when ICMP packets are enqueued onto the error queue,
>> sk_err is also set. Before f5f99309fa74 (sock: do not set sk_err
>> in sock_dequeue_err_skb), a subsequent error queue read
>> would set sk_err to the next error on the queue, or 0 if empty.
>> As no error types other than ICMP set this field, sk_err should
>> not be modified upon dequeuing them.
>>
>> Only for ICMP errors, reset the (racy) sk_err. Some applications,
>> like traceroute, rely on it and go into a futile busy POLLERR
>> loop otherwise.
>>
>> In principle, sk_err has to be set while an ICMP error is queued.
>> Testing is_icmp_err_skb(skb_next) approximates this without
>> requiring a full queue walk. Applications that receive both ICMP
>> and other errors cannot rely on this legacy behavior, as other
>> errors do not set sk_err in the first place.
>>
>> Fixes: f5f99309fa74 (sock: do not set sk_err in sock_dequeue_err_skb)
>> Signed-off-by: Soheil Hassas Yeganeh <soh...@google.com>
>> Signed-off-by: Willem de Bruijn <will...@google.com>
>>     Acked-by: Eric Dumazet <eduma...@google.com>
>> Acked-by: Maciej Żenczykowski <m...@google.com>
>> Signed-off-by: David S. Miller <da...@davemloft.net>
>>
>> Cheers,
>> Vito Caputo
>>
>>
>> - Forwarded message from l...@pengaru.com -
>>
>> Date: Thu, 16 Feb 2017 03:17:49 -0800
>> From: l...@pengaru.com
>> To: linux-kernel@vger.kernel.org
>> Subject: Re: [BUG] 4.10-rc8 - ping spinning?
>> User-Agent: Mutt/1.5.23 (2014-03-12)
>>
>> On Thu, Feb 16, 2017 at 03:03:03AM -0800, l...@pengaru.com wrote:
>>> Hello list,
>>>
>>> Some rtl8192cu bugs of old got me in the habit of running ping in a shelved 
>>> (i.e. forgotten) xterm, a harmless practice which seemed to prevent the 
>>> rtl8192cu device from dying.
>>>
>>> This evening the system started getting very slow and to my surprise I found
>>> this in `top`:
>>>  5115 swivel30  10   14772   1928   1756 R  90.9  0.0   1351:41 ping
>>>  9005 swivel30  10   14772   1892   1724 R  90.9  0.0   1354:26 ping
>>>
>>> This is a dual core machine (X61s, core2

Re: [BUG] 4.10-rc8 - ping spinning?

2017-02-16 Thread Soheil Hassas Yeganeh 
On Thu, Feb 16, 2017 at 10:50 AM, Soheil Hassas Yeganeh
 wrote:
> Thank you Vito for the report.
>
> The patch you cited actually resolves a similar backward compatibility
> problem for traceroute.
>
> I suspect the problem here is that there's a local error queued on the
> error queue after an ICMP message. ping apparently expect the
> sk->sk_err to be set for the local errors as well, and hence the
> error. Ideally, ping should read the error queue if there an EPOLLERR,
> because local errors never sk->sk_err on their own. That is, if we
> have

[oops] That is, if we have only one local error on the error queue, we
cannot rely on having an error on recvmsg (i.e., sk->sk_err being set)
even in 4.9.

Thanks,
Soheil

> But as a workaround, would you mind trying the following patch to see
> if it resolves the issue reported?
>
> From: Soheil Hassas Yeganeh 
> Date: Thu, 16 Feb 2017 10:48:24 -0500
> ---
>  net/core/skbuff.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 734c71468b01..2b774b564024 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -3717,7 +3717,8 @@ EXPORT_SYMBOL(sock_queue_err_skb);
>  static bool is_icmp_err_skb(const struct sk_buff *skb)
>  {
>   return skb && (SKB_EXT_ERR(skb)->ee.ee_origin == SO_EE_ORIGIN_ICMP ||
> -   SKB_EXT_ERR(skb)->ee.ee_origin == SO_EE_ORIGIN_ICMP6);
> +   SKB_EXT_ERR(skb)->ee.ee_origin == SO_EE_ORIGIN_ICMP6 ||
> +   SKB_EXT_ERR(skb)->ee.ee_origin == SO_EE_ORIGIN_LOCAL);
>  }
>
>  struct sk_buff *sock_dequeue_err_skb(struct sock *sk)
> --
>
> Thanks!
> Soheil
>
> On Thu, Feb 16, 2017 at 7:05 AM,   wrote:
>> Hello netdev,
>>
>> Please see the forwarded message below.  This was sent to linux-kernel but
>> after digging a little I suspect it's specific to the network stack.
>>
>> Perusing the net/ changes between 4.9 and 4.10-rc8 this sounded awful related
>> to what I'm observing:
>>
>> commit 83a1a1a70e87f676fbb6086b26b6ac7f7fdd107d
>> Author: Soheil Hassas Yeganeh 
>> Date:   Wed Nov 30 14:01:08 2016 -0500
>>
>> sock: reset sk_err for ICMP packets read from error queue
>>
>> Only when ICMP packets are enqueued onto the error queue,
>> sk_err is also set. Before f5f99309fa74 (sock: do not set sk_err
>> in sock_dequeue_err_skb), a subsequent error queue read
>> would set sk_err to the next error on the queue, or 0 if empty.
>> As no error types other than ICMP set this field, sk_err should
>> not be modified upon dequeuing them.
>>
>> Only for ICMP errors, reset the (racy) sk_err. Some applications,
>> like traceroute, rely on it and go into a futile busy POLLERR
>> loop otherwise.
>>
>> In principle, sk_err has to be set while an ICMP error is queued.
>> Testing is_icmp_err_skb(skb_next) approximates this without
>> requiring a full queue walk. Applications that receive both ICMP
>> and other errors cannot rely on this legacy behavior, as other
>> errors do not set sk_err in the first place.
>>
>> Fixes: f5f99309fa74 (sock: do not set sk_err in sock_dequeue_err_skb)
>> Signed-off-by: Soheil Hassas Yeganeh 
>>     Signed-off-by: Willem de Bruijn 
>> Acked-by: Eric Dumazet 
>> Acked-by: Maciej Żenczykowski 
>> Signed-off-by: David S. Miller 
>>
>> Cheers,
>> Vito Caputo
>>
>>
>> - Forwarded message from l...@pengaru.com -
>>
>> Date: Thu, 16 Feb 2017 03:17:49 -0800
>> From: l...@pengaru.com
>> To: linux-kernel@vger.kernel.org
>> Subject: Re: [BUG] 4.10-rc8 - ping spinning?
>> User-Agent: Mutt/1.5.23 (2014-03-12)
>>
>> On Thu, Feb 16, 2017 at 03:03:03AM -0800, l...@pengaru.com wrote:
>>> Hello list,
>>>
>>> Some rtl8192cu bugs of old got me in the habit of running ping in a shelved 
>>> (i.e. forgotten) xterm, a harmless practice which seemed to prevent the 
>>> rtl8192cu device from dying.
>>>
>>> This evening the system started getting very slow and to my surprise I found
>>> this in `top`:
>>>  5115 swivel30  10   14772   1928   1756 R  90.9  0.0   1351:41 ping
>>>  9005 swivel30  10   14772   1892   1724 R  90.9  0.0   1354:26 ping
>>>
>>> This is a dual core machine (X61s, core2duo 1.8Ghz), those processes are
>>> burning all the free CPU in the system context.  They're identical commands,
>>> just plain `ping domain.com`, to the same host.  It appears I accidentally
>>> (fortuitous

Re: [BUG] 4.10-rc8 - ping spinning?

2017-02-16 Thread Soheil Hassas Yeganeh 
Thank you Vito for the report.

The patch you cited actually resolves a similar backward compatibility
problem for traceroute.

I suspect the problem here is that there's a local error queued on the
error queue after an ICMP message. ping apparently expect the
sk->sk_err to be set for the local errors as well, and hence the
error. Ideally, ping should read the error queue if there an EPOLLERR,
because local errors never sk->sk_err on their own. That is, if we
have

But as a workaround, would you mind trying the following patch to see
if it resolves the issue reported?

From: Soheil Hassas Yeganeh <soh...@google.com>
Date: Thu, 16 Feb 2017 10:48:24 -0500
---
 net/core/skbuff.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 734c71468b01..2b774b564024 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3717,7 +3717,8 @@ EXPORT_SYMBOL(sock_queue_err_skb);
 static bool is_icmp_err_skb(const struct sk_buff *skb)
 {
  return skb && (SKB_EXT_ERR(skb)->ee.ee_origin == SO_EE_ORIGIN_ICMP ||
-   SKB_EXT_ERR(skb)->ee.ee_origin == SO_EE_ORIGIN_ICMP6);
+   SKB_EXT_ERR(skb)->ee.ee_origin == SO_EE_ORIGIN_ICMP6 ||
+   SKB_EXT_ERR(skb)->ee.ee_origin == SO_EE_ORIGIN_LOCAL);
 }

 struct sk_buff *sock_dequeue_err_skb(struct sock *sk)
-- 

Thanks!
Soheil

On Thu, Feb 16, 2017 at 7:05 AM,  <l...@pengaru.com> wrote:
> Hello netdev,
>
> Please see the forwarded message below.  This was sent to linux-kernel but
> after digging a little I suspect it's specific to the network stack.
>
> Perusing the net/ changes between 4.9 and 4.10-rc8 this sounded awful related
> to what I'm observing:
>
> commit 83a1a1a70e87f676fbb6086b26b6ac7f7fdd107d
> Author: Soheil Hassas Yeganeh <soh...@google.com>
> Date:   Wed Nov 30 14:01:08 2016 -0500
>
> sock: reset sk_err for ICMP packets read from error queue
>
> Only when ICMP packets are enqueued onto the error queue,
> sk_err is also set. Before f5f99309fa74 (sock: do not set sk_err
> in sock_dequeue_err_skb), a subsequent error queue read
> would set sk_err to the next error on the queue, or 0 if empty.
> As no error types other than ICMP set this field, sk_err should
> not be modified upon dequeuing them.
>
> Only for ICMP errors, reset the (racy) sk_err. Some applications,
> like traceroute, rely on it and go into a futile busy POLLERR
> loop otherwise.
>
> In principle, sk_err has to be set while an ICMP error is queued.
> Testing is_icmp_err_skb(skb_next) approximates this without
> requiring a full queue walk. Applications that receive both ICMP
> and other errors cannot rely on this legacy behavior, as other
> errors do not set sk_err in the first place.
>
> Fixes: f5f99309fa74 (sock: do not set sk_err in sock_dequeue_err_skb)
> Signed-off-by: Soheil Hassas Yeganeh <soh...@google.com>
> Signed-off-by: Willem de Bruijn <will...@google.com>
> Acked-by: Eric Dumazet <eduma...@google.com>
> Acked-by: Maciej Żenczykowski <m...@google.com>
> Signed-off-by: David S. Miller <da...@davemloft.net>
>
> Cheers,
> Vito Caputo
>
>
> - Forwarded message from l...@pengaru.com -
>
> Date: Thu, 16 Feb 2017 03:17:49 -0800
> From: l...@pengaru.com
> To: linux-kernel@vger.kernel.org
> Subject: Re: [BUG] 4.10-rc8 - ping spinning?
> User-Agent: Mutt/1.5.23 (2014-03-12)
>
> On Thu, Feb 16, 2017 at 03:03:03AM -0800, l...@pengaru.com wrote:
>> Hello list,
>>
>> Some rtl8192cu bugs of old got me in the habit of running ping in a shelved  
>>(i.e. forgotten) xterm, a harmless practice which seemed to prevent the   
>>   rtl8192cu device from dying.
>>
>> This evening the system started getting very slow and to my surprise I found
>> this in `top`:
>>  5115 swivel30  10   14772   1928   1756 R  90.9  0.0   1351:41 ping
>>  9005 swivel30  10   14772   1892   1724 R  90.9  0.0   1354:26 ping
>>
>> This is a dual core machine (X61s, core2duo 1.8Ghz), those processes are
>> burning all the free CPU in the system context.  They're identical commands,
>> just plain `ping domain.com`, to the same host.  It appears I accidentally
>> (fortuitously?) had two running, which made this event more interesting.
>>
>> I can assert that these did not begin spinning simultaneously - as you can 
>> see
>> by the cumulative time in `top` there's a small delta.  I also use a window
>> manager with builtin continuous process monitoring, and when I noticed this 
>> was
>> happening I was able to see that one of the processes had only recently begun
>> spinning, the other was spinning long eno

Re: [BUG] 4.10-rc8 - ping spinning?

2017-02-16 Thread Soheil Hassas Yeganeh 
Thank you Vito for the report.

The patch you cited actually resolves a similar backward compatibility
problem for traceroute.

I suspect the problem here is that there's a local error queued on the
error queue after an ICMP message. ping apparently expect the
sk->sk_err to be set for the local errors as well, and hence the
error. Ideally, ping should read the error queue if there an EPOLLERR,
because local errors never sk->sk_err on their own. That is, if we
have

But as a workaround, would you mind trying the following patch to see
if it resolves the issue reported?

From: Soheil Hassas Yeganeh 
Date: Thu, 16 Feb 2017 10:48:24 -0500
---
 net/core/skbuff.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 734c71468b01..2b774b564024 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3717,7 +3717,8 @@ EXPORT_SYMBOL(sock_queue_err_skb);
 static bool is_icmp_err_skb(const struct sk_buff *skb)
 {
  return skb && (SKB_EXT_ERR(skb)->ee.ee_origin == SO_EE_ORIGIN_ICMP ||
-   SKB_EXT_ERR(skb)->ee.ee_origin == SO_EE_ORIGIN_ICMP6);
+   SKB_EXT_ERR(skb)->ee.ee_origin == SO_EE_ORIGIN_ICMP6 ||
+   SKB_EXT_ERR(skb)->ee.ee_origin == SO_EE_ORIGIN_LOCAL);
 }

 struct sk_buff *sock_dequeue_err_skb(struct sock *sk)
-- 

Thanks!
Soheil

On Thu, Feb 16, 2017 at 7:05 AM,   wrote:
> Hello netdev,
>
> Please see the forwarded message below.  This was sent to linux-kernel but
> after digging a little I suspect it's specific to the network stack.
>
> Perusing the net/ changes between 4.9 and 4.10-rc8 this sounded awful related
> to what I'm observing:
>
> commit 83a1a1a70e87f676fbb6086b26b6ac7f7fdd107d
> Author: Soheil Hassas Yeganeh 
> Date:   Wed Nov 30 14:01:08 2016 -0500
>
> sock: reset sk_err for ICMP packets read from error queue
>
> Only when ICMP packets are enqueued onto the error queue,
> sk_err is also set. Before f5f99309fa74 (sock: do not set sk_err
> in sock_dequeue_err_skb), a subsequent error queue read
> would set sk_err to the next error on the queue, or 0 if empty.
> As no error types other than ICMP set this field, sk_err should
> not be modified upon dequeuing them.
>
> Only for ICMP errors, reset the (racy) sk_err. Some applications,
> like traceroute, rely on it and go into a futile busy POLLERR
> loop otherwise.
>
> In principle, sk_err has to be set while an ICMP error is queued.
> Testing is_icmp_err_skb(skb_next) approximates this without
> requiring a full queue walk. Applications that receive both ICMP
> and other errors cannot rely on this legacy behavior, as other
> errors do not set sk_err in the first place.
>
> Fixes: f5f99309fa74 (sock: do not set sk_err in sock_dequeue_err_skb)
> Signed-off-by: Soheil Hassas Yeganeh 
> Signed-off-by: Willem de Bruijn 
> Acked-by: Eric Dumazet 
> Acked-by: Maciej Żenczykowski 
> Signed-off-by: David S. Miller 
>
> Cheers,
> Vito Caputo
>
>
> - Forwarded message from l...@pengaru.com -
>
> Date: Thu, 16 Feb 2017 03:17:49 -0800
> From: l...@pengaru.com
> To: linux-kernel@vger.kernel.org
> Subject: Re: [BUG] 4.10-rc8 - ping spinning?
> User-Agent: Mutt/1.5.23 (2014-03-12)
>
> On Thu, Feb 16, 2017 at 03:03:03AM -0800, l...@pengaru.com wrote:
>> Hello list,
>>
>> Some rtl8192cu bugs of old got me in the habit of running ping in a shelved  
>>(i.e. forgotten) xterm, a harmless practice which seemed to prevent the   
>>   rtl8192cu device from dying.
>>
>> This evening the system started getting very slow and to my surprise I found
>> this in `top`:
>>  5115 swivel30  10   14772   1928   1756 R  90.9  0.0   1351:41 ping
>>  9005 swivel30  10   14772   1892   1724 R  90.9  0.0   1354:26 ping
>>
>> This is a dual core machine (X61s, core2duo 1.8Ghz), those processes are
>> burning all the free CPU in the system context.  They're identical commands,
>> just plain `ping domain.com`, to the same host.  It appears I accidentally
>> (fortuitously?) had two running, which made this event more interesting.
>>
>> I can assert that these did not begin spinning simultaneously - as you can 
>> see
>> by the cumulative time in `top` there's a small delta.  I also use a window
>> manager with builtin continuous process monitoring, and when I noticed this 
>> was
>> happening I was able to see that one of the processes had only recently begun
>> spinning, the other was spinning long enough to have its start fall off the
>> chart (at least ~17 minutes ago).
>>
>> This hasn't occurred before AFAIK, but I haven't spent much time in 4.10 yet.
>> I'm pretty confident

Re: [BUG] 4.10-rc8 - ping spinning?

2017-02-16 Thread lkml 
Hello netdev,

Please see the forwarded message below.  This was sent to linux-kernel but
after digging a little I suspect it's specific to the network stack.

Perusing the net/ changes between 4.9 and 4.10-rc8 this sounded awful related
to what I'm observing:

commit 83a1a1a70e87f676fbb6086b26b6ac7f7fdd107d
Author: Soheil Hassas Yeganeh <soh...@google.com>
Date:   Wed Nov 30 14:01:08 2016 -0500

sock: reset sk_err for ICMP packets read from error queue

Only when ICMP packets are enqueued onto the error queue,
sk_err is also set. Before f5f99309fa74 (sock: do not set sk_err
in sock_dequeue_err_skb), a subsequent error queue read
would set sk_err to the next error on the queue, or 0 if empty.
As no error types other than ICMP set this field, sk_err should
not be modified upon dequeuing them.

Only for ICMP errors, reset the (racy) sk_err. Some applications,
like traceroute, rely on it and go into a futile busy POLLERR
loop otherwise.

In principle, sk_err has to be set while an ICMP error is queued.
Testing is_icmp_err_skb(skb_next) approximates this without
requiring a full queue walk. Applications that receive both ICMP
and other errors cannot rely on this legacy behavior, as other
errors do not set sk_err in the first place.

Fixes: f5f99309fa74 (sock: do not set sk_err in sock_dequeue_err_skb)
Signed-off-by: Soheil Hassas Yeganeh <soh...@google.com>
Signed-off-by: Willem de Bruijn <will...@google.com>
Acked-by: Eric Dumazet <eduma...@google.com>
Acked-by: Maciej Żenczykowski <m...@google.com>
Signed-off-by: David S. Miller <da...@davemloft.net>

Cheers,
Vito Caputo


- Forwarded message from l...@pengaru.com -

Date: Thu, 16 Feb 2017 03:17:49 -0800
From: l...@pengaru.com
To: linux-kernel@vger.kernel.org
Subject: Re: [BUG] 4.10-rc8 - ping spinning?
User-Agent: Mutt/1.5.23 (2014-03-12)

On Thu, Feb 16, 2017 at 03:03:03AM -0800, l...@pengaru.com wrote:
> Hello list,
> 
> Some rtl8192cu bugs of old got me in the habit of running ping in a shelved   
>   (i.e. forgotten) xterm, a harmless practice which seemed to prevent the 
> rtl8192cu device from dying.
> 
> This evening the system started getting very slow and to my surprise I found
> this in `top`:
>  5115 swivel30  10   14772   1928   1756 R  90.9  0.0   1351:41 ping
>  9005 swivel30  10   14772   1892   1724 R  90.9  0.0   1354:26 ping
> 
> This is a dual core machine (X61s, core2duo 1.8Ghz), those processes are
> burning all the free CPU in the system context.  They're identical commands,
> just plain `ping domain.com`, to the same host.  It appears I accidentally
> (fortuitously?) had two running, which made this event more interesting.
> 
> I can assert that these did not begin spinning simultaneously - as you can see
> by the cumulative time in `top` there's a small delta.  I also use a window
> manager with builtin continuous process monitoring, and when I noticed this 
> was
> happening I was able to see that one of the processes had only recently begun
> spinning, the other was spinning long enough to have its start fall off the
> chart (at least ~17 minutes ago).
> 
> This hasn't occurred before AFAIK, but I haven't spent much time in 4.10 yet.
> I'm pretty confident this didn't happen in 4.9 which I ran for quite a while.
> 
> `strace` of one of the aforementioned processes:
> 
> 1487241315.073568 poll([{fd=3, events=POLLIN|POLLERR}], 1, 927) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.22>
> 1487241315.073665 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.20>
> 1487241315.073747 gettimeofday({1487241315, 73774}, NULL) = 0 <0.21>
> 1487241315.073829 poll([{fd=3, events=POLLIN|POLLERR}], 1, 927) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.25>
> 1487241315.073927 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.20>
> 1487241315.074024 gettimeofday({1487241315, 74050}, NULL) = 0 <0.000256>
> 1487241315.074352 poll([{fd=3, events=POLLIN|POLLERR}], 1, 927) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.26>
> 1487241315.076241 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.22>
> 1487241315.076337 gettimeofday({1487241315, 76366}, NULL) = 0 <0.20>
> 1487241315.076422 poll([{fd=3, events=POLLIN|POLLERR}], 1, 924) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.25>
> 1487241315.076523 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.25>
> 1487241315.079770 gettimeofday({1487241315, 79799}, NULL) = 0 <0.19>
> 1487241315.079855 poll([{fd=3, events=POLLIN|POLLERR}], 1, 921) = 1 ([{fd

Re: [BUG] 4.10-rc8 - ping spinning?

2017-02-16 Thread lkml 
Hello netdev,

Please see the forwarded message below.  This was sent to linux-kernel but
after digging a little I suspect it's specific to the network stack.

Perusing the net/ changes between 4.9 and 4.10-rc8 this sounded awful related
to what I'm observing:

commit 83a1a1a70e87f676fbb6086b26b6ac7f7fdd107d
Author: Soheil Hassas Yeganeh 
Date:   Wed Nov 30 14:01:08 2016 -0500

sock: reset sk_err for ICMP packets read from error queue

Only when ICMP packets are enqueued onto the error queue,
sk_err is also set. Before f5f99309fa74 (sock: do not set sk_err
in sock_dequeue_err_skb), a subsequent error queue read
would set sk_err to the next error on the queue, or 0 if empty.
As no error types other than ICMP set this field, sk_err should
not be modified upon dequeuing them.

Only for ICMP errors, reset the (racy) sk_err. Some applications,
like traceroute, rely on it and go into a futile busy POLLERR
loop otherwise.

In principle, sk_err has to be set while an ICMP error is queued.
Testing is_icmp_err_skb(skb_next) approximates this without
requiring a full queue walk. Applications that receive both ICMP
and other errors cannot rely on this legacy behavior, as other
errors do not set sk_err in the first place.

Fixes: f5f99309fa74 (sock: do not set sk_err in sock_dequeue_err_skb)
Signed-off-by: Soheil Hassas Yeganeh 
Signed-off-by: Willem de Bruijn 
Acked-by: Eric Dumazet 
Acked-by: Maciej Żenczykowski 
Signed-off-by: David S. Miller 

Cheers,
Vito Caputo


- Forwarded message from l...@pengaru.com -

Date: Thu, 16 Feb 2017 03:17:49 -0800
From: l...@pengaru.com
To: linux-kernel@vger.kernel.org
Subject: Re: [BUG] 4.10-rc8 - ping spinning?
User-Agent: Mutt/1.5.23 (2014-03-12)

On Thu, Feb 16, 2017 at 03:03:03AM -0800, l...@pengaru.com wrote:
> Hello list,
> 
> Some rtl8192cu bugs of old got me in the habit of running ping in a shelved   
>   (i.e. forgotten) xterm, a harmless practice which seemed to prevent the 
> rtl8192cu device from dying.
> 
> This evening the system started getting very slow and to my surprise I found
> this in `top`:
>  5115 swivel30  10   14772   1928   1756 R  90.9  0.0   1351:41 ping
>  9005 swivel30  10   14772   1892   1724 R  90.9  0.0   1354:26 ping
> 
> This is a dual core machine (X61s, core2duo 1.8Ghz), those processes are
> burning all the free CPU in the system context.  They're identical commands,
> just plain `ping domain.com`, to the same host.  It appears I accidentally
> (fortuitously?) had two running, which made this event more interesting.
> 
> I can assert that these did not begin spinning simultaneously - as you can see
> by the cumulative time in `top` there's a small delta.  I also use a window
> manager with builtin continuous process monitoring, and when I noticed this 
> was
> happening I was able to see that one of the processes had only recently begun
> spinning, the other was spinning long enough to have its start fall off the
> chart (at least ~17 minutes ago).
> 
> This hasn't occurred before AFAIK, but I haven't spent much time in 4.10 yet.
> I'm pretty confident this didn't happen in 4.9 which I ran for quite a while.
> 
> `strace` of one of the aforementioned processes:
> 
> 1487241315.073568 poll([{fd=3, events=POLLIN|POLLERR}], 1, 927) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.22>
> 1487241315.073665 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.20>
> 1487241315.073747 gettimeofday({1487241315, 73774}, NULL) = 0 <0.21>
> 1487241315.073829 poll([{fd=3, events=POLLIN|POLLERR}], 1, 927) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.25>
> 1487241315.073927 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.20>
> 1487241315.074024 gettimeofday({1487241315, 74050}, NULL) = 0 <0.000256>
> 1487241315.074352 poll([{fd=3, events=POLLIN|POLLERR}], 1, 927) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.26>
> 1487241315.076241 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.22>
> 1487241315.076337 gettimeofday({1487241315, 76366}, NULL) = 0 <0.20>
> 1487241315.076422 poll([{fd=3, events=POLLIN|POLLERR}], 1, 924) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.25>
> 1487241315.076523 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.25>
> 1487241315.079770 gettimeofday({1487241315, 79799}, NULL) = 0 <0.19>
> 1487241315.079855 poll([{fd=3, events=POLLIN|POLLERR}], 1, 921) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.24>
> 1487241315.079956 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily una

Re: [BUG] 4.10-rc8 - ping spinning?

2017-02-16 Thread lkml 
On Thu, Feb 16, 2017 at 03:03:03AM -0800, l...@pengaru.com wrote:
> Hello list,
> 
> Some rtl8192cu bugs of old got me in the habit of running ping in a shelved   
>   (i.e. forgotten) xterm, a harmless practice which seemed to prevent the 
> rtl8192cu device from dying.
> 
> This evening the system started getting very slow and to my surprise I found
> this in `top`:
>  5115 swivel30  10   14772   1928   1756 R  90.9  0.0   1351:41 ping
>  9005 swivel30  10   14772   1892   1724 R  90.9  0.0   1354:26 ping
> 
> This is a dual core machine (X61s, core2duo 1.8Ghz), those processes are
> burning all the free CPU in the system context.  They're identical commands,
> just plain `ping domain.com`, to the same host.  It appears I accidentally
> (fortuitously?) had two running, which made this event more interesting.
> 
> I can assert that these did not begin spinning simultaneously - as you can see
> by the cumulative time in `top` there's a small delta.  I also use a window
> manager with builtin continuous process monitoring, and when I noticed this 
> was
> happening I was able to see that one of the processes had only recently begun
> spinning, the other was spinning long enough to have its start fall off the
> chart (at least ~17 minutes ago).
> 
> This hasn't occurred before AFAIK, but I haven't spent much time in 4.10 yet.
> I'm pretty confident this didn't happen in 4.9 which I ran for quite a while.
> 
> `strace` of one of the aforementioned processes:
> 
> 1487241315.073568 poll([{fd=3, events=POLLIN|POLLERR}], 1, 927) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.22>
> 1487241315.073665 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.20>
> 1487241315.073747 gettimeofday({1487241315, 73774}, NULL) = 0 <0.21>
> 1487241315.073829 poll([{fd=3, events=POLLIN|POLLERR}], 1, 927) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.25>
> 1487241315.073927 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.20>
> 1487241315.074024 gettimeofday({1487241315, 74050}, NULL) = 0 <0.000256>
> 1487241315.074352 poll([{fd=3, events=POLLIN|POLLERR}], 1, 927) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.26>
> 1487241315.076241 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.22>
> 1487241315.076337 gettimeofday({1487241315, 76366}, NULL) = 0 <0.20>
> 1487241315.076422 poll([{fd=3, events=POLLIN|POLLERR}], 1, 924) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.25>
> 1487241315.076523 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.25>
> 1487241315.079770 gettimeofday({1487241315, 79799}, NULL) = 0 <0.19>
> 1487241315.079855 poll([{fd=3, events=POLLIN|POLLERR}], 1, 921) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.24>
> 1487241315.079956 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.21>
> 1487241315.080057 gettimeofday({1487241315, 80084}, NULL) = 0 <0.20>
> 1487241315.080140 poll([{fd=3, events=POLLIN|POLLERR}], 1, 921) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.24>
> 1487241315.080238 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.21>
> 1487241315.080322 gettimeofday({1487241315, 80350}, NULL) = 0 <0.20>
> 1487241315.080406 poll([{fd=3, events=POLLIN|POLLERR}], 1, 920) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.23>
> 1487241315.080502 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.19>
> 1487241315.080583 gettimeofday({1487241315, 80610}, NULL) = 0 <0.18>
> 1487241315.080663 poll([{fd=3, events=POLLIN|POLLERR}], 1, 920) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.24>
> 1487241315.080761 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.20>
> 1487241315.080843 gettimeofday({1487241315, 80870}, NULL) = 0 <0.20>
> 1487241315.080925 poll([{fd=3, events=POLLIN|POLLERR}], 1, 920) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.37>
> 1487241315.081037 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.20>
> 1487241315.081119 gettimeofday({1487241315, 81147}, NULL) = 0 <0.20>
> 

It's worth noting that ping is still otherwise functioning correctly, despite
the POLLERR:

1487242826.169502 sendmsg(3, {msg_name(16)={sa_family=AF_INET, 
sin_port=htons(0), sin_addr=inet_addr("xx.xxx.xxx.xxx")}, 
msg_iov(1)=[{"\10\0\245G\23\373\243uJ\206\245X\0\0\0\0\352\225\2\0\0\0\0\0\20\21\22\23\24\25\26\27"...,
 64}], msg_controllen=0, msg_flags=0}, MSG_CONFIRM) = 64 <0.000133>
1487242826.169757 recvmsg(3, {msg_name(16)={sa_family=AF_INET, 
sin_port=htons(0), sin_addr=inet_addr("66.240.222.126")}, msg_iov(1)=[{"E 
\0T\345\364\0\0002\1w\23B\360\336~\n\0\0\23\0\0\255G\23\373\243uJ\206\245X"..., 
192}], msg_controllen=32, {cmsg_len=32, cmsg_level=SOL_SOCKET, cmsg_type=0x1d 
/* SCM_??? */, ...},

Re: [BUG] 4.10-rc8 - ping spinning?

2017-02-16 Thread lkml 
On Thu, Feb 16, 2017 at 03:03:03AM -0800, l...@pengaru.com wrote:
> Hello list,
> 
> Some rtl8192cu bugs of old got me in the habit of running ping in a shelved   
>   (i.e. forgotten) xterm, a harmless practice which seemed to prevent the 
> rtl8192cu device from dying.
> 
> This evening the system started getting very slow and to my surprise I found
> this in `top`:
>  5115 swivel30  10   14772   1928   1756 R  90.9  0.0   1351:41 ping
>  9005 swivel30  10   14772   1892   1724 R  90.9  0.0   1354:26 ping
> 
> This is a dual core machine (X61s, core2duo 1.8Ghz), those processes are
> burning all the free CPU in the system context.  They're identical commands,
> just plain `ping domain.com`, to the same host.  It appears I accidentally
> (fortuitously?) had two running, which made this event more interesting.
> 
> I can assert that these did not begin spinning simultaneously - as you can see
> by the cumulative time in `top` there's a small delta.  I also use a window
> manager with builtin continuous process monitoring, and when I noticed this 
> was
> happening I was able to see that one of the processes had only recently begun
> spinning, the other was spinning long enough to have its start fall off the
> chart (at least ~17 minutes ago).
> 
> This hasn't occurred before AFAIK, but I haven't spent much time in 4.10 yet.
> I'm pretty confident this didn't happen in 4.9 which I ran for quite a while.
> 
> `strace` of one of the aforementioned processes:
> 
> 1487241315.073568 poll([{fd=3, events=POLLIN|POLLERR}], 1, 927) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.22>
> 1487241315.073665 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.20>
> 1487241315.073747 gettimeofday({1487241315, 73774}, NULL) = 0 <0.21>
> 1487241315.073829 poll([{fd=3, events=POLLIN|POLLERR}], 1, 927) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.25>
> 1487241315.073927 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.20>
> 1487241315.074024 gettimeofday({1487241315, 74050}, NULL) = 0 <0.000256>
> 1487241315.074352 poll([{fd=3, events=POLLIN|POLLERR}], 1, 927) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.26>
> 1487241315.076241 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.22>
> 1487241315.076337 gettimeofday({1487241315, 76366}, NULL) = 0 <0.20>
> 1487241315.076422 poll([{fd=3, events=POLLIN|POLLERR}], 1, 924) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.25>
> 1487241315.076523 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.25>
> 1487241315.079770 gettimeofday({1487241315, 79799}, NULL) = 0 <0.19>
> 1487241315.079855 poll([{fd=3, events=POLLIN|POLLERR}], 1, 921) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.24>
> 1487241315.079956 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.21>
> 1487241315.080057 gettimeofday({1487241315, 80084}, NULL) = 0 <0.20>
> 1487241315.080140 poll([{fd=3, events=POLLIN|POLLERR}], 1, 921) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.24>
> 1487241315.080238 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.21>
> 1487241315.080322 gettimeofday({1487241315, 80350}, NULL) = 0 <0.20>
> 1487241315.080406 poll([{fd=3, events=POLLIN|POLLERR}], 1, 920) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.23>
> 1487241315.080502 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.19>
> 1487241315.080583 gettimeofday({1487241315, 80610}, NULL) = 0 <0.18>
> 1487241315.080663 poll([{fd=3, events=POLLIN|POLLERR}], 1, 920) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.24>
> 1487241315.080761 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.20>
> 1487241315.080843 gettimeofday({1487241315, 80870}, NULL) = 0 <0.20>
> 1487241315.080925 poll([{fd=3, events=POLLIN|POLLERR}], 1, 920) = 1 ([{fd=3, 
> revents=POLLERR}]) <0.37>
> 1487241315.081037 recvmsg(3, 0x7ffc8e05e260, MSG_DONTWAIT) = -1 EAGAIN 
> (Resource temporarily unavailable) <0.20>
> 1487241315.081119 gettimeofday({1487241315, 81147}, NULL) = 0 <0.20>
> 

It's worth noting that ping is still otherwise functioning correctly, despite
the POLLERR:

1487242826.169502 sendmsg(3, {msg_name(16)={sa_family=AF_INET, 
sin_port=htons(0), sin_addr=inet_addr("xx.xxx.xxx.xxx")}, 
msg_iov(1)=[{"\10\0\245G\23\373\243uJ\206\245X\0\0\0\0\352\225\2\0\0\0\0\0\20\21\22\23\24\25\26\27"...,
 64}], msg_controllen=0, msg_flags=0}, MSG_CONFIRM) = 64 <0.000133>
1487242826.169757 recvmsg(3, {msg_name(16)={sa_family=AF_INET, 
sin_port=htons(0), sin_addr=inet_addr("66.240.222.126")}, msg_iov(1)=[{"E 
\0T\345\364\0\0002\1w\23B\360\336~\n\0\0\23\0\0\255G\23\373\243uJ\206\245X"..., 
192}], msg_controllen=32, {cmsg_len=32, cmsg_level=SOL_SOCKET, cmsg_type=0x1d 
/* SCM_??? */, ...},