netdev - Re: [GIT] Networking

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Message-ID: <AANLkTin32jUnBtHF-EAkSMnFQM6cTbn-G3NZQJ3xjTWU@mail.gmail.com>
Date:	Thu, 20 Jan 2011 13:12:52 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	David Miller <davem@...emloft.net>
Cc:	akpm@...ux-foundation.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [GIT] Networking

On Wed, Jan 19, 2011 at 6:04 PM, David Miller <davem@...emloft.net> wrote:
>
> 1) Revert a netlink flag sanity check that is causing regressions in
>   existing applications.
...

This is a long-shot, but I thought I'd ask before I start trying to
bisect the fourth independent suspend/resume related issue in this
merge window..

When I suspend/resume while logged in by closing the lid on my laptop
on FC14, it causes the gnome-screensaver-dialog to start up. So far so
fine, that's what I want, and it all works fin in 2.6.37.

But in current -git (and in -rc8, so it's not changed by your latest
pull request), gnome-screensaver-dialog gets stuck after I type in my
password, making the box basically useless.

So I straced it over the network, and if I attach _when_ it is already
stuck, it immediately becomes unstuck.  But if I attach to it before
typing my password, I can see the hang in strace, and it looks like
this:

  ...
  read(3, 0x9806500, 4096)                = -1 EAGAIN (Resource
temporarily unavailable)
  poll([{fd=4, events=POLLIN}, {fd=3, events=POLLIN}, {fd=12,
events=POLLIN|POLLPRI}, {fd=14, events=POLLIN|POLLPRI}, {fd=9,
events=POLLIN|POLLPRI}, {fd=10, events=POLLIN|POLLPRI}, {fd=15,
events=POLLIN}, {fd=16, events=POLLIN}, {fd=17, events=0}, {fd=19,
events=POLLIN}], 10, -1) = ? ERESTART_RESTARTBLOCK (To be restarted)
  restart_syscall(

and that's it - it's now hung. So why did it work when I straced it
while hung? And why is it doing that ERESTART_RESTARTBLOCK in the
first place, I'm not seeing any signals there?

So I tried sending it a useless signal, which will re-animate the
strace, and now I get:

  restart_syscall(<... resuming interrupted call ...>) = 1
  --- SIGWINCH (Window changed) @ 0 (0) ---
  poll([{fd=3, events=POLLIN|POLLOUT}], 1, -1) = 1 ([{fd=3, revents=POLLOUT}])

Whee. That signal got it started again, and the poll finished immediately.

And how/why did the input to the poll apparently change? That looks
suspicious too. Might be some odd strace artifact, but whatever.

So I'm contacting you because that fd=3 is a socket (I didn't check
details), and because anything I find in the git logs that discusses
"poll" seems to be network-related. So I'm wondering it this rings any
bells, because bisecting this is going to be painful as hell (since I
have to carefully work around all the _other_ problems I've bisected
on that machine while doing so).

                           Linus
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