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xen: disable interrupts before saving in percpu 

Impact: Fix race condition

xen_mc_batch has a small preempt race where it takes the address of a
percpu variable immediately before disabling interrupts, thereby
leaving a small window in which we may migrate to another cpu and save
the flags in the wrong percpu variable.  Disable interrupts before
saving the old flags in a percpu.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
Jeremy Fitzhardinge 2009-02-03 16:01:46 -08:00 committed by H. Peter Anvin
parent b1792e3670
commit 06fc732c33
1 changed files with 3 additions and 1 deletions
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4
arch/x86/xen/multicalls.h
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@ -19,8 +19,10 @@ DECLARE_PER_CPU(unsigned long, xen_mc_irq_flags);
paired with xen_mc_issue() */
static inline void xen_mc_batch(void)
{
unsigned long flags;
/* need to disable interrupts until this entry is complete */
local_irq_save(__get_cpu_var(xen_mc_irq_flags));
local_irq_save(flags);
__get_cpu_var(xen_mc_irq_flags) = flags;
}
static inline struct multicall_space xen_mc_entry(size_t args)