From: Marcelo Tosatti <mtosatti@redhat.com>
Date: Thu, 8 May 2008 22:47:01 +0000 (-0300)
Subject: KVM: Fix kvm_vcpu_block() task state race
X-Git-Tag: v2.6.26-rc4~122^2~2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e5c239cfd5b0ec22751c099dbf4d91f3c504a64f;p=pandora-kernel.git

KVM: Fix kvm_vcpu_block() task state race

There's still a race in kvm_vcpu_block(), if a wake_up_interruptible()
call happens before the task state is set to TASK_INTERRUPTIBLE:

CPU0                            CPU1

kvm_vcpu_block

add_wait_queue

kvm_cpu_has_interrupt = 0
                                set interrupt
                                if (waitqueue_active())
                                        wake_up_interruptible()

kvm_cpu_has_pending_timer
kvm_arch_vcpu_runnable
signal_pending

set_current_state(TASK_INTERRUPTIBLE)
schedule()

Can be fixed by using prepare_to_wait() which sets the task state before
testing for the wait condition.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
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