netdev - Re: ppoll() stuck on POLLIN while TCP peer is sending

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Date:	Tue, 08 Jan 2013 18:14:07 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Eric Wong <normalperson@...t.net>
Cc:	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: ppoll() stuck on POLLIN while TCP peer is sending

On Tue, 2013-01-08 at 23:23 +0000, Eric Wong wrote:
> Mel Gorman <mgorman@...e.de> wrote:
> > Please try the following patch. However, even if it works the benefit of
> > capture may be so marginal that partially reverting it and simplifying
> > compaction.c is the better decision.
> 
> I already got my VM stuck on this one.  I had two twosleepy instances,
> 2774 was the one that got stuck (also confirmed by watching top).
> 
> Btw, have you been able to reproduce this on your end?
> 
> I think the easiest reproduction on my 2-core VM is by running 2
> twosleepy processes and doing the following to dirty a lot of pages:

Given the persistent sk_stream_wait_memory() traces I suspect a plain
TCP bug, triggered by some extra wait somewhere.

Please mm guys don't spend too much time right now, I'll try to
reproduce the problem.

Don't be confused by sk_stream_wait_memory() name.
A thread is stuck here because TCP stack is failing to wake it.



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