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04c44a080d
xen_irq_enable_direct and xen_sysexit were using "andw $0x00ff, XEN_vcpu_info_pending(vcpu)" to unmask events and test for pending ones in one instuction. Unfortunately, the pending flag must be modified with a locked operation since it can be set by another CPU, and the unlocked form of this operation was causing the pending flag to get lost, allowing the processor to return to usermode with pending events and ultimately deadlock. The simple fix would be to make it a locked operation, but that's rather costly and unnecessary. The fix here is to split the mask-clearing and pending-testing into two instructions; the interrupt window between them is of no concern because either way pending or new events will be processed. This should fix lingering bugs in using direct vcpu structure access too. [ Stable: needed in 2.6.24.x ] Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Cc: Stable <stable@kernel.org> Signed-off-by: Ingo Molnar <mingo@elte.hu> |
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