Re: [bug] stuck localhost TCP connections, v2.6.26-rc3+

Ingo Molnar
2008-05-26T16:24:10Z

* Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> wrote:

> On Mon, 26 May 2008, Ingo Molnar wrote:
>
> > there's a hung distcc task on the system, waiting for socket action
> > forever:
> >
> > [root@europe ~]# strace -fp 19578
> > Process 19578 attached - interrupt to quit
> > select(5, NULL, [4], [4], {82, 90000} <unfinished ...>
>
> Hmm, readfds is NULL isn't it?!? Are you sure you straced the right
> process?

yes, i'm stracing the task that is hung unexpectedly.

> > disturbing that task via strace did not change the state of the
> > socket - and that's not unexpected as it's a select(). [TCP state
> > might be affected if strace impacted a recvmsg or a sendmsg wait
> > directly.]
>
> I fail to understand this paragraph due to excessive negation... :-)

i mean, sometimes a TCP connection can get 'unstuck' if you strace a
task - that is because the TCP related syscall the task sits in gets
interrupted. But in this case it's select() which doesnt explicitly take
the socket, doesnt do any tcp_push_pending_frames() processing, etc. -
it just its on the socket waitqueue AFAICS. And that's expected.

Ingo