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Subject[PATCH] xen: disable interrupts before saving in percpu
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>
---
arch/x86/xen/multicalls.h | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

===================================================================
--- a/arch/x86/xen/multicalls.h
+++ b/arch/x86/xen/multicalls.h
@@ -19,8 +19,10 @@
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)



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