tree d02bbb6713f47e3cd26643c36d2dcada0ff1dccc
parent 577eebeae34d340685d8985dfdb7dfe337c511e8
author Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> 1252524831 -0700
committer Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> 1252539491 -0700

xen: only enable interrupts while actually blocking for spinlock

Where possible we enable interrupts while waiting for a spinlock to
become free, in order to reduce big latency spikes in interrupt handling.

However, at present if we manage to pick up the spinlock just before
blocking, we'll end up holding the lock with interrupts enabled for a
while.  This will cause a deadlock if we recieve an interrupt in that
window, and the interrupt handler tries to take the lock too.

Solve this by shrinking the interrupt-enabled region to just around the
blocking call.

[ Impact: avoid race/deadlock when using Xen PV spinlocks ]

Reported-by: "Yang, Xiaowei" <xiaowei.yang@intel.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>