Igor and Maxim,
all stack traces I reported before were caused by glibc bug in CentOS that corrupted memory. It was the reason on nginx faul in random place. I's sorry for taking your time and thanks for loooking into this issue.
In CentOs MALLOC_CHECK_ is enabled by default. And causes memory corruption for applications.
More info is here: http://www.pubbs.net/200911/kde/23500-deactivate-malloccheck-on-x8664.html
Patch to fix it is here: http://sourceware.org/bugzilla/show_bug.cgi?id=10282
So it's possible to fix glibc or export MALLOC_CHECK_=3 to avoid random crashes (which unfirtunatelly began happen after enabling cache).