Ldm sometimes hangs at logout

[Alkis Georgopoulos]

Binary package hint: ldm

Hi,

My TCs had a problem of ldm hanging at logout, waiting for an already-finished process (the ssh connection) to finish.

The problem was in sshutils.c:
> ldm_wait(pid);
> read(ldm.sshfd, buf, sizeof buf); /* clear any exit message so ssh can exit cleanly */
> ldm_wait(ldm.sshpid);

where in my slow terminals half of the time "sshpid" finished before "pid", so ldm_wait got mixed up and waited 2 times for "sshpid".

To solve this, in ldm.c I had to change
- res = waitid (P_ALL, 0, &info, WEXITED | WSTOPPED);
+ res = waitid (P_PID, pid, &info, WEXITED | WSTOPPED);
so that ldm_wait only waits for the SPECIFIED child, and not for ANY child.

I also had to do the following changes in sshutils.c:
+ fcntl(ldm.sshfd, F_SETFL, O_NONBLOCK);
to make the following clean-up call non-blocking:
read(ldm.sshfd, buf, sizeof buf);

Even though I didn't experience any problems with it, I also thought it would be nice to change the "read" above to a "while" so that it flushes sshfd even for size > sizeof buf.

A last note, in ldm_wait I don't think the "while" is needed anymore, because it waits for the specific child it was called for. I tried it without the "while" and it works fine, but I'm not sending it to keep the proposed changes to a minimum. Of course I can send it if you like.

Kind regards,
Alkis Georgopoulos

alkisg@alkis:~$ LANG=en dpkg -l ltsp* && sudo chroot /opt/ltsp/i386 dpkg -l ltsp*
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Cfg-files/Unpacked/Failed-cfg/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Hold/Reinst-required/X=both-problems (Status,Err: uppercase=bad)
||/ Name Version Description
+++-=================================-=================================-==================================================================================
ii ltsp-server 5.1.65-0ubuntu2 Basic LTSP server environment
ii ltsp-server-standalone 5.1.65-0ubuntu2 Complete LTSP server environment
un ltsp-utils <none> (no description available)
ii ltspfs 0.5.10-0ubuntu1 Fuse based remote filesystem for LTSP thin clients
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Cfg-files/Unpacked/Failed-cfg/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Hold/Reinst-required/X=both-problems (Status,Err: uppercase=bad)
||/ Όνομα Έκδοση Περιγραφή
+++-=================================-=================================-==================================================================================
ii ltsp-client 5.1.65-0ubuntu2 LTSP client environment
ii ltsp-client-core 5.1.65-0ubuntu2 LTSP client environment
ii ltspfsd 0.5.10-0ubuntu1 Fuse based remote filesystem daemon for LTSP thin clients

[Ryan Niebur (ryan52)]

crap, sorry for forgetting to look at this. if somebody else wants to, go ahead.

[Stéphane Graber (stgraber)]

Fixed in latest ldm for Karmic.

[Steve Cayford (cayfo001)]

Is there a fix or work-around available for Jaunty?

[Alkis Georgopoulos (alkisg)]

You may use stgraber's ppa if you want, there's a backported jaunty version of ltsp there: https://launchpad.net/~stgraber/+archive/ppa

[Steve Cayford (cayfo001)]

Thanks. I'll try that.