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| author | Jeremy Fitzhardinge <jeremy@goop.org> | 2009-02-03 16:01:46 -0800 |
|---|---|---|
| committer | H. Peter Anvin <hpa@zytor.com> | 2009-02-03 17:22:40 -0800 |
| commit | 06fc732c33a7ff5e4c91bcf4a6ca86b5e335ad9a (patch) | |
| tree | eb6a202f5bc01a5c8ac9f7245b9097f18ac44e57 | |
| parent | b1792e367053968f2ddb48bc911d314143ce6242 (diff) | |
| download | lwn-06fc732c33a7ff5e4c91bcf4a6ca86b5e335ad9a.tar.gz lwn-06fc732c33a7ff5e4c91bcf4a6ca86b5e335ad9a.zip | |
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>
| -rw-r--r-- | arch/x86/xen/multicalls.h | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/arch/x86/xen/multicalls.h b/arch/x86/xen/multicalls.h index 858938241616..fa3e10725d98 100644 --- a/arch/x86/xen/multicalls.h +++ b/arch/x86/xen/multicalls.h @@ -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) |