netdev - Re: 4.4-rc7 failure report

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Message-ID: <1451502526.8255.48.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 30 Dec 2015 14:08:46 -0500
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	davej@...emonkey.org.uk, daniel@...earbox.net,
	alexei.starovoitov@...il.com, dledford@...hat.com,
	netdev@...r.kernel.org
Subject: Re: 4.4-rc7 failure report

On Wed, 2015-12-30 at 12:50 -0500, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Wed, 30 Dec 2015 11:55:25 -0500
> 
> > On Wed, 2015-12-30 at 10:11 -0500, Dave Jones wrote:
> >> On Wed, Dec 30, 2015 at 10:38:56AM +0100, Daniel Borkmann wrote:
> >> 
> >>  > Given that this drop doesn't strictly need to be caused by filter code,
> >>  > it would be nice if you could pin the location down where the packet gets
> >>  > dropped exactly. Perhaps dropwatch or perf with '-e skb:kfree_skb -a -g
> >>  > dhclient <iface>', etc could help to get a first overview to dig into
> >>  > details then.
> >> 
> >> Wild stab in the dark, but..
> >> Could this bug be another symptom fixed by http://article.gmane.org/gmane.linux.network/392885 ?
> > 
> > dhclient does not use async io
> 
> But the bug causes requests to "LOOK" like async I/O, right?


This is not how I understood the bug.

By having a bit set (because we lacked a clear of wq->flags), we have :

sock_wake_async()
...
case SOCK_WAKE_WAITD:
	if (test_bit(SOCKWQ_ASYNC_WAITDATA, &wq->flags))
		break; 

So we never call kill_fasync()




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