apache 2.4 - apache2 mod-php cpu 100% on process

I have a VPS Debian server with Apache 2.4.10 mod-php. Server starts normally, but after some time I get 100% cpu on one of www-data processes and a web-server becomes unavailable.

I tried strace on that procces and I got an infinite loop of these lines:

poll([{fd=93, events=POLLIN}], 1, 3000) = 1 ([{fd=93, revents=POLLHUP}])
read(93, "", 13160)

Then I tried lsof ant got this:

COMMAND  PID     USER   FD   TYPE DEVICE SIZE/OFF       NODE NAME

apache2 1134 www-data   93r  FIFO    0,8      0t0 3176528027 pipe

What can cause the problem? When I restart apache, after some time I have the same behavior.