Re: [uml-devel] glibc and NPTL, problem, workarounds, etc.

[BlaisorBlade <blaisorblade_spam@yahoo.it>]

On Wednesday 08 September 2004 21:02, William Stearns wrote:
> Good day, all,
> 	Zaphod had a rather nasty filesystem crash last week.  It happened
> around the time that two other events happened; the raid array forgot it
> had drive 3 (requiring me to remove and re-add the drive and start a raid
> rebuild), and one of the users was attempting to upgrade glibc on debian.
> This put in a new version of glibc, along with the NPTL (Native Posix
> Threading Libraries) that don't work with UML.  From that point, that user
> could log in with ssh, but could no longer run any applications because
> bash refused to fork.

> 	There are a couple of workarounds for this problem.  First, when
> installing any root filesystem, check afterwards to see if there's a
> directory called /lib/tls/ .  If so, rename or delete it.  This removes
> the NPTL extensions to glibc but leaves glibc itself, so applications
> continue to work; they just never try to use the NPTL extensions.
> 	To make sure it's never used again, do the following as root:

There is another patch which should make the work - (I never tested it, but it 
should work). Basically, uname will state it is a "i586" rather than "i686", 
so NPTL is not enabled:

http://www.suse.de/~kraxel/uml/patches/uml-pretend-to-be-i586

> rm -rf /lib/tls/
> mkdir /lib/tls/
> chmod 000 /lib/tls/
> chattr +i /lib/tls/

> 	Now even root can't write to that directory.  Any attempt to
> install a new version of glibc will probably fail because rpm/apt can't
> write to that directory, but it's better than having a non-functioning
> system.

> 	In trying to run the above commands while fixing his system, I ran
> into the problem where the commands I wanted to run loaded glibc and the
> NPTL libaries, and therefore refused to run (the error message I got on
> fork mentioned "nptl").  In fact, running single user mode (starting up
> uml with "ro single init=/bin/bash") didn't do any better since bash
> needed to fork to run the above commands and the fork failed.
> 	The workaround to the above is this:
>
> export LD_ASSUME_KERNEL=2.4.1
> exec /bin/bash

> 	which replaces your current bash with a new one that won't try to
> load the nptl libraries.  Now you can run commands even though the
> /lib/tls/ directory is there - this would be an excellent time to remove
> them.  :-)

> 	Jeff, I have a seriously hard time believing that simply running
> nptl binaries could cause journal errors out on the host.

You got them on the *physical* host? Yup!

> I'm much more 
> inclined to believe that the raid rebuild might have briefly set the block
> devices read-only
No, it shouldn't have - I didn't write the RAID code, but I'm sure that 
anything such is not allowed to happen.

Did the machine poweroff/crash/oops during the rebuild?

I've lately discovered (and fixed) a big number of problems with the SKAS 
patch, and somebody reported a host crash while running Java in UML which 
could be connected to one of the SKAS bugs.
> , long enough for the journal to give up because there's 
> no place to put the data. 
Ok, there is something more similar that could, actually, have happened. The 
device does not become "read only" at all - the stripe which is being 
processed will probably be locked for a while, which means that the datas 
will wait to be written for a while. Then, if memory is exhausted, the 
journal will get errors.
> I just thought I'd bring up the closesness in 
> time in case it triggered any connections for you.

> 	I do have some of the host journal errors if they're useful, but I
> suspect they're not.
Please post the messages (without flooding us with debug datas - post only 
what is easily human-readable, and redirect the rest to the LKML, the 
filesystem ML and to the RAID ml, if any).

Also, which is the filesystem you use?

Bye
-- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729



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