Re: [leafnode-list] Reproducibly truncate groupinfo

[Matthias Andree <ma@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>]

krasel@xxxxxxxxxxxxxxxxxxxxxxxxxxxx (Cornelius Krasel) writes:

> Matthias Andree wrote:
> 
> > I slightly modified writeactive and caught these:
> > 
> > Jun 13 11:16:47 emma1 leafnode[15058]: cannot open new groupinfo file: \
> >   file already exists
> 
> Yuck. This should have caught by the locking mechanism.

This is the counterexample that tells us the current locking scheme is
violable. 

I'll just try to use the linux trace toolkit to track this down and see
if it's an artifact or the locking itself and report more details.

> Would it be a good idea to modify your additional code as follows to
> avoid the problem of concurrent processes writing to the groupinfo file?

No, it will just hide the race and in the end things will be worse. 

The locking needs to be in place so that the groupinfo is reread before
being modified.

My idea about the separate groupinfo daemon wasn't forged out of thin
air.

BTW, I'd like to thank Jörg Dietrich for insisting that there is a
problem and showing a way to reproduce it.

-- 
Matthias Andree

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