Re: System blocks (hangs) on ifconfig up

[Eric Dumazet <eric.dumazet@gmail.com>]

Le lundi 13 décembre 2010 à 11:14 +0200, Shmulik Hen a écrit :
> On 12/13/2010 01:03 AM, Ben Hutchings wrote:
> > On Sun, 2010-12-12 at 17:00 +0200, Shmulik Hen wrote:
> >> Hello,
> >>
> >> My system is Ubuntu 10.04, running kernel 2.6.32-26-generic.
> >>
> >> Whenever I try to bring up a specific ethernet interface for the second
> >> time, my
> >> system becomes unresponsive for 60 seconds - i.e. no mouse, no keyboard, no
> >> screen refresh. etc.
> >>
> >> Looking at the driver's code, I could see that it's dev->open() method calls
> >> wait_event_interruptible_timeout() with a timeout of 60 seconds - exactly
> >> the delay I'm seeing.
> > That seems like a stupid thing for it to do.
> I agree...
> >> I have narrowed the code to a bare minimum (see below - loosely based on
> >> dummy.c), which only calls mdelay(10000) in it's dev->open() method, and
> >> still, my system blocks for exactly 10 seconds when I run the following
> >> sequence:
> >>
> >>   >  sudo ifconfig shmulik0 up
> >>   >  sudo ifconfig shmulik0 down
> >>   >  sudo ifconfig shmulik0 up
> >>
> >> At this point - the system is stuck for 10 seconds.
> > Bringing an interface up or down is a synchronous operation and is
> > serialised with most other network configuration operations.  So this is
> > the expected behaviour.
> >
> > Ben.
> But why does this happen only the second time I run ifconfig up?
> How come the entire system is totally frozen?
> I can't even switch to other applications running. If I run 'top' in another
> console, it stops refreshing for the entire period.
> 
> I'll try to explain better;
> The driver I'm referring to is part of an embedded system development kit.
> It runs on the controlling side, which may be a PC or some Linux embedded
> system. It exposes a virtual interface that allows to communicate via
> ethernet connection to a remote board, and performs the firmware download
> to that board.
> Unfortunately, the firmware download stage is  done during dev->open() of
> this virtual interface. The call to wait_event_interruptible_timeout()
> is there to make sure the boot process of the remote board is complete via a
> message. If all goes well the first time, there is no delay, but if the 
> operation
> fails for any reason the first time, and a second attempt is made (another
> ifconfig up), we see the freezing.
> 
> Since this driver is (mostly) closed source, I had to try and reproduce 
> the situation
> in an all open-source driver - this is the sample code I attached to my 
> original
> message. The call to mdelay() there is meant to simulate the delay of 
> the original
> driver - it schedules.
> 

mdelay() does a busy wait. If you are not SMP, this means a 'freeze'

If you want to schedule, you should use msleep()

> Obviously, the correct way to fix this is to separate the firmware 
> download part
> from the dev->open() method, but this is not as simple as it may sound - I'm
> currently working on this. In the mean time I'm looking for a simpler 
> solution
> (or answer) to our problem.
> 
> I'll appreciate any insight on this matter.
> 
>      Thanks in advance,
>      Shmulik Hen.