Hi Steve,
On 7/11/12 8:43 AM, Steven Rostedt wrote:
On Tue, 2012-07-10 at 16:32 -0400, Dong Liu wrote:
Hi All,
Because I could not find a solution for the cpu stall problem on kernel
3.2.18-rt29. I thought I might try an older kernel. So I download
linux-2.6.33.9 and patch-2.6.33.9-rt31. But 2.6.33 doesn't have
vhost_net, so I ported vhost_net from 2.6.34 back to 2.6.33.9.
The kernel was patched and built successfully. But when I boot, I got
kernel NULL pointer dereference error. After the error, my system seems
stable, I can start KVM client without CPU stalls. But very frequently,
processes will locked up for long time, the wchan displayed by ps is
either sync_page or synchronize_rcu. It looks that rcu still causes
problem in the rt-kernel.
The dmesg out of NULL pointer is attached.
Um, when you get one of those 'kernel NULL pointer' crashes, the system
is not in a good state. If the crash happened to a task that holds a
mutex or worse a spinlock, it will never release it. That means, any new
task that tries to take that same mutex or spinlock, will just block and
sit there.
Thus, those processes that are stuck at either sync_page or
synchronize_rcu, are probably waiting for that processes to release a
mutex, or finish something else that it will never do.
Basically, once you see a NULL pointer dereference, it's time to save
the dmesg and reboot the box.
I finally tracked down the NULL pointer is caused by
echo -n "0" > /sys/kernel/kexec_crash_size
in /etc/init/kexec-disable.conf.
After I disabled, no more kernel NULL pointer dereference. But I still
got cpu stall :(
Thanks,
Dong
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