mysqld dies on connection close

[fimbultyr]

Hi there!

Recently, I noticed some strange CPU load on one of my gentoo servers. A short investigation turned out that several mysqld threads were struggling for CPU time.
I restarted MySQL and everything looked normal again, but after a few minutes one of the mysqld threads was using 100% CPU time on one core again.

After an entire afternoon of error searching this is what I came up with:
As soon as any client (I've tried the mysql command line client, php and telnet) closes a connection to the mysql server the mysqld thread which handled the connection starts to spinlock somehow. It doesn't matter whether I connect via TCP/IP or an UNIX domain socket, but while the connection is alive everything works fine. I can issue querys, create/drop tables and databases, etc.
So obviously something with the socket handling is broken.
Since I've encountered strange software failures before running a hardened gentoo system I suspected the hardened toolchain or the kernel for causing the problems.

Here is what I tried so far:

• Switched to a non ~amd64 masked mysql version
  
• Compiled mysql with a non-hardened toolchain
  
• Disabled IPv6 networking
  
• Booted a kernel without any Grsecurity / PaX features
  
• Re-emerged all mysql dependencies (emerge -ave dev-db/mysql)
  
• Tested a completely empty database by killing /var/lib/mysql
  
• Countless combinations of the above...
  

Unfortunately nothing helped to resolve the issue and therefore I hope that somebody here who has more experience with mysql will be able to help.

Kind regards,
fimbultyr

emerge --info:

[Janne Pikkarainen]

Do logs contain any MySQL error?
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