perf on 2.6.38-rc4 wedges my box

[Jeff Moyer <jmoyer@redhat.com>]

Hi,

I'm trying out willy's ata_ram driver[1], and in so doing have managed to
wedge my box while using perf record on an aio-stress run:

[root@metallica ~]# modprobe ata_ram capacity=2097152 preallocate=1
[root@metallica ~]# ./aio-stress -O -o 0 -r 4 -d 32 -b 16 /dev/sds
adding stage write
starting with write
file size 1024MB, record size 4KB, depth 32, ios per iteration 8
max io_submit 16, buffer alignment set to 4KB
threads 1 files 1 contexts 1 context offset 2MB verification off
adding file /dev/sds thread 0
write on /dev/sds (621.30 MB/s) 1024.00 MB in 1.65s
thread 0 write totals (621.27 MB/s) 1024.00 MB in 1.65s
[root@metallica ~]# perf record -- ./aio-stress -O -o 0 -r 4 -d 32 -b 16
/dev/sds
adding stage write
starting with write
file size 1024MB, record size 4KB, depth 32, ios per iteration 8
max io_submit 16, buffer alignment set to 4KB
threads 1 files 1 contexts 1 context offset 2MB verification off
adding file /dev/sds thread 0

and there it sits.  On the console, I see:

NOHZ: local_softirq_pending 100
NOHZ: local_softirq_pending 100
NOHZ: local_softirq_pending 100
NOHZ: local_softirq_pending 100
NOHZ: local_softirq_pending 100

The number of messages varies, but this is the most I've seen (it
doesn't keep repeating).  At this point, the machine does not respond to
pings.  As I don't have physical access at the moment, I can't try
alt-sysrq, but might be able to do that tomorrow.  It's probably worth
noting that I've witnessed similar behavior with real devices, so it's
not just the ata_ram driver.

Any ideas on how to track this down?

Thanks!

Jeff

[1] http://git.kernel.org/?p=linux/kernel/git/willy/misc.git;a=shortlog;h=refs/heads/ata-ram