Bug 470304

+++ This bug was initially created as a clone of Bug #450953 +++

Description of problem:

After running an arbitrary workload involving network traffic for some time (1-2
days), a xen guest running the 2.6.9-67 x86_64 xenU kernel locks up with both
vcpu's spinning at 100%.  

Version-Release number of selected component (if applicable):
kernel-2.6.9-67

How reproducible:
Reproduces after running a test workload (involving network traffic) for 1-2
days, but not consistently.

Steps to Reproduce:
1. Run a test workload involving network traffic
2. monitor cpu usage of guest
3. wait... until guest cpu usage goes to 100%
  
Actual results:
Guest kernel spins on both vcpu's

Expected results:
Guest kernel doesn't spin

Additional info:
The problem is due to a race between the scheduler and network interrupts.  On
one vcpu, the scheduler takes the runqueue spinlock of the other vcpu to
schedule a process, and attempts to lock mm_unpinned_lock.  On the other vcpu,
another process is holding mm_unpinned_lock (because it is starting or exiting),
and is interrupted by a network interrupt.  The network interrupt handler
attempts to wake up the same process that the first vcpu is trying to schedule,
and will try to get the runqueue spinlock that the first vcpu is already holding.

I was not able to obtain a full kernel stack from the interrupt, but do have
kernel stacks of the tasks on the vcpu's, if needed.

--- Additional comment from herbert.van.den.bergh on 2008-06-11 17:13:09 EDT ---

Created an attachment (id=309000)
fix for mm_unpinned_lock / runq deadlock


--- Additional comment from riel on 2008-07-30 11:17:56 EDT ---

The patch looks good to me.

--- Additional comment from pm-rhel on 2008-09-03 09:17:16 EDT ---

Updating PM score.

--- Additional comment from pm-rhel on 2008-09-17 14:52:15 EDT ---

This request was evaluated by Red Hat Product Management for inclusion in a Red
Hat Enterprise Linux maintenance release.  Product Management has requested
further review of this request by Red Hat Engineering, for potential
inclusion in a Red Hat Enterprise Linux Update release for currently deployed
products.  This request is not yet committed for inclusion in an Update
release.