nginx worker crashes, grsec denial

I have a Xen guest which is having problems with nginx and grsec.
Worker processes for nginx fail when HTTP requests are made.

Each request leaves messages much like these:
[  800.424417] nginx[7540]: segfault at 8 ip 00000c513b8ba644 sp
00007138a2675300 error 4 in nginx[c513b882000+f0000]
[  800.424428] grsec: From 202.76.166.249: Segmentation fault occurred
at 0000000000000008 in /usr/sbin/nginx[nginx:7540] uid/euid:102/102
gid/egid:247/247, parent /usr/sbin/nginx[nginx:7389] uid/euid:0/0
gid/egid:0/0
[  800.424435] grsec: From 202.76.166.249: bruteforce prevention
initiated for the next 30 minutes or until service restarted, stalling
each fork 30 seconds.  Please investigate the crash report for
/usr/sbin/nginx[nginx:7540] uid/euid:102/102 gid/egid:247/247, parent
/usr/sbin/nginx[nginx:7389] uid/euid:0/0 gid/egid:0/0
[  800.424441] grsec: From 202.76.166.249: denied resource overstep by
requesting 4096 for RLIMIT_CORE against limit 0 for
/usr/sbin/nginx[nginx:7540] uid/euid:102/102 gid/egid:247/247, parent
/usr/sbin/nginx[nginx:7389] uid/euid:0/0 gid/egid:0/0

It would be great if someone could tell me what sysctl options or
kernel options I can change to fix this in the short term. It might
take me a while to understand the problem better and it would be good
to have the system running.

This system has changed recently from a VirtualBox guest to being a
Xen guest. So the kernel is built differently, I am using the
grsecurity defaults for a Xen guest with performance priorities. It
ran fine as a VirtualBox guest.

Let me know if you need more info.

-- 
www.johntate.org