workaround for glibc bug

[Thiago Macieira]

Em Friday 28 September 2007 17:08:04 Gary L. Greene Jr. escreveu:
> On Thursday 27 September 2007 11:27:04 pm Thiago Macieira wrote:
> > Matthew Woehlke wrote:
> > >Thiago Macieira wrote:
> > >> We add to KDE 4.0 Release Notes: "if you're on Linux and you're not
> > >> using glibc version 2.6.xxx, you might experience freezes. Upgrade."
> > >
> > >Does this mean I can't run KDE4 (safely)? I have to use my box for
> > >development also, and upgrading to libc versions none of our other boxes
> > >use isn't necessarily condoned.
> >
> > No. If you don't upgrade, you will have the option between freezes and
> > slowness (LD_BIND_NOW=1).
>
> Updating to a new glibc isn't a trivial task.... That being said, I know
> that AltimatOS won't be releasing with 2.6.x, since we're too far along
> toward release. additionally doing a check of another distro's tree, looks
> like Mandriva 2008.0 will be on 2.6.1 from checking the repo of cooker,
> which isn't too far from release either, so this is going to bite at least
> these two distributions. since Matthias said that 2.6.91 was needed for the
> fix.

The bug appears when resolving symbols in two threads at the same time. So, to 
get rid of it, we need to get rid of one of the three conditions of the 
problem:
  a) two threads
  b) resolving symbols
  c) at the same time

We don't control (c). I don't think anyone is seriously suggesting we stop 
using threads. And doing a full-static solution (no symbol resolution) is not 
possible. 

But we can control a+b+c: i.e. resolve all symbols when only one thread is 
running. That's LD_BIND_NOW=1 and that causes slowness.

BTW, a+c is the bug solution: put a mutex locking around the functions doing 
resolution.

Distributions probably can backport the solution. I won't comment on how 
trivial or complex that task is. That's why we need to get the word out now, 
so that they have time to do it.

-- 
  Thiago Macieira  -  thiago (AT) macieira.info - thiago (AT) kde.org
    PGP/GPG: 0x6EF45358; fingerprint:
    E067 918B B660 DBD1 105C  966C 33F5 F005 6EF4 5358
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