netdev - Re: [GIT] Networking

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Message-Id: <201101202228.00400.rjw@sisk.pl>
Date:	Thu, 20 Jan 2011 22:28:00 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	David Miller <davem@...emloft.net>, akpm@...ux-foundation.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Tejun Heo <tj@...nel.org>
Subject: Re: [GIT] Networking

On Thursday, January 20, 2011, Linus Torvalds wrote:
> 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).

This is a long shot too, but perhaps it's related to

8cfe400 Freezer: Fix a race during freezing of TASK_STOPPED tasks

(adding Tejun to the CC just in case).

Rafael
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