oqgraph-dev team mailing list archive

[Heinz Wiesinger <HMWiesinger@xxxxxxxxxxx>]

On Monday 02 June 2014 13:23:54 Sergei Golubchik wrote:
> Hi, Andrew!
> 
> On Jun 02, Andrew McDonnell wrote:
> > Hi all
> > 
> > (Cross-posted to oqgraph-developers, maria-developers)
> > 
> > I am trying to track down a segfault apparently triggered by concurrent
> > execution of queries through OQGraph - for context, see:
> > 
> > https://mariadb.atlassian.net/browse/MDEV-6282
> > 
> > I am however a bit confused as to what is going on, because at least some
> > of the information leads me to suspect that there could be more going on
> > here than just a simple race condition.
> > 
> > --Immediate Cause--
> > 
> > On the surface, a segfault appears to be caused in a method in
> > sql_class.h,
> > Statement::check_limit_rows_examined() dereferencing a NULL pointer,
> > `lex`.
> > The method check_limit_rows_examined() was called from sql_class.h method
> > handler::increment_statistics() .
> 
> I don't see how thd->lex could be NULL there. It shouldn't be changed
> concurrently on anything.
> 
> Can you actually repeat the crash?

I haven't been able so far to come up with a nice, contained, general test 
case. However, I can very easily reproduce the crash, on both a CentOS 6 
system using MariaDB's rpms as well as on my Slackware systems using a self-
compiled version.

Grs,
Heinz

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