Re: Hanging udev process on nfs-mounted /dev

[Frank Steiner <fsteiner-mail@bio.ifi.lmu.de>]

Kay Sievers wrote

>>Seems we have two different problems here, one that sounds like a loop
>>consuming all the CPU and onother one, like the trace, which looks like
>>a F_SETLKW deadlock.
>>The traces are indicating a deadlock, where processes are simply waiting
>>for each other for a write-lock on the udev.tdb to be released.

That would match my observation that there seemed to be 2-3 udev processes
started almost at the same time. Since I recorded all the udev traces
with the ppid in the log name, I could see that there were always three
processes started close together (the log files having the same timestamp
and the ppids not differing much, like pids 29465, 29470 and 29473), so
they might deadlock.

However, also note that these problems so far occured only on hosts
having /dev/ mounted via NFS. Maybe the slow NFS traffic (in comparison
to the local hard disk) is well-suited for triggering the deadlock.

> Here is a patch that implements a timeout for the dead udev process. After
> 20 seconds the lock system call is interrupted and the error debug from tdb
> is logged to the syslog. I needed to port the sleep() calls, cause they
> are not compatible with alarm().

Thanks for the patch, I will apply it and try to reproduce the situations!
If I get a log, I will send it here.

A general question: Someone on the NFS mailing list proposed to remove
the NFS mount for dev and replace it by some tmpfs mounted on /dev.
SuSE is not really prepared for it, so udevstart misses a lot of devices
like /dev/stderr etc., but I could hack this myself easily.
Is it safe to assume that one should have less problems with a tmpfs
dev compared to a NFS mount?

cu,
Frank
-- 
Dipl.-Inform. Frank Steiner   Web:  http://www.bio.ifi.lmu.de/~steiner/
Lehrstuhl f. Bioinformatik    Mail: http://www.bio.ifi.lmu.de/~steiner/m/
LMU, Amalienstr. 17           Phone: +49 89 2180-4049
80333 Muenchen, Germany       Fax:   +49 89 2180-99-4049
* Rekursion kann man erst verstehen, wenn man Rekursion verstanden hat. *


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