[BRLTTY] BRLTTY Implicated In Resource Exhaustion

[Sabahattin Gucukoglu]

On 8 May 2011, at 12:53, Jason White wrote:
> Sabahattin Gucukoglu <mail at sabahattin-gucukoglu.com> wrote:
>> I don't know which resource, though.  All I know is that the kernel keeps
>> running, and those services which don't require new threads and processes
>> keep running (DNS).  But the keyboard is unusable, even for ctrl+alt+del,
>> and so the only option is to hard reboot the box.
> 
> Can you log in over ssh from another machine?

I can connect, but not log in.  Process can't start.  I've not yet tried being logged in and using busybox when this happens, but I will if it comes to it.

> Have you tried
> echo 1 > /proc/sys/kernel/sched_autogroup_enabled
> to invoke the per session group scheduling in 2.6.38, which might help if it's
> a CPU issue?

It didn't work, which seems to make sense since I'm not always logged in when it happens.  I did notice, though, that it seemed to be triggered by action on the terminals, either console or display.  Also, brltty seems to die instantly if started up via SSH, as opposed to a VT.

> Have you collected information from top, vmstat, ps, etc., to determine which
> processes are using the most memory and CPU?

I have stripped down the system to the bare essentials, and still not found anything particularly unusual or harmful (as in, normal and non-extreme memory, CPU and disk, and while the lockup condition wasn't in effect, since I couldn't afterwards).  I did however take the chance to get rid of HAL, which had the heaviest CPU-bound processes for handling the BrailleNote's ActiveSync connection via SynCE/RAPI2/PPP.  Barely works nowadays anyway.  Well it does, but only if you mess around with it for long enough.  It didn't help, unfortunately.  So basically, nothing abnormal.

>> Uname -a output: Linux Bloodstone 2.6.38-2-686 #1 SMP Sat Apr 23 19:04:20
>> UTC 2011 i686 GNU/Linux (The latest Debian unstable kernel.)
>> 
>> BRLTTY 4.2; BrlAPI server 0.5.5 (The latest "brltty" package in Debian
>> Unstable.)
> 
> I'm running debian unstable here, kernel 2.6.38 x86-64, BRLTTY 4.2, braille
> display connected via a USB interface, and no stability issues.

I don't know.  Obviously it may not be BRLTTY itself causing the issue, but something that it does clearly makes the system unhappy.  I am turning on debugging in brltty and will also begin stracing it if that doesn't turn up any answers.

Oh yes, one more interesting effect this had was to make the system speaker beep forever if the key I pressed was backspace at an empty shell line.  So even the kernel console driver isn't working right.  Of course it could just be very, very, very slow, but anyway I couldn't figure out anything else before having to reset the machine.

Cheers,
Sabahattin