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

Eric Dumazet
2013-01-09T02:14:12Z

On Tue, 2013-01-08 at 23:23 +0000, Eric Wong wrote:
> Mel Gorman <mgorman@suse.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.