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Subject[PATCH] KVM: Deal with nested sleeps in kvm_vcpu_block()
From
Previously this code assumed nothing would mess with current->state
between the set_current_state() and schedule(). However the call to
kvm_vcpu_check_block() in between might end up requiring locks or other
actions, which would change current->state. A similar pattern was
described in the "The problem with nested sleeping primitives" LWN
article[0].

[0] https://lwn.net/Articles/628628

Signed-off-by: Space Meyer <spm@google.com>
---
virt/kvm/kvm_main.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index fab4d37905785..64e10d73f2a92 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -32,6 +32,7 @@
#include <linux/sched/signal.h>
#include <linux/sched/mm.h>
#include <linux/sched/stat.h>
+#include <linux/wait.h>
#include <linux/cpumask.h>
#include <linux/smp.h>
#include <linux/anon_inodes.h>
@@ -3426,6 +3427,7 @@ static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
*/
bool kvm_vcpu_block(struct kvm_vcpu *vcpu)
{
+ DEFINE_WAIT_FUNC(vcpu_block_wait, woken_wake_function);
struct rcuwait *wait = kvm_arch_vcpu_get_wait(vcpu);
bool waited = false;

@@ -3437,13 +3439,11 @@ bool kvm_vcpu_block(struct kvm_vcpu *vcpu)
preempt_enable();

for (;;) {
- set_current_state(TASK_INTERRUPTIBLE);
-
if (kvm_vcpu_check_block(vcpu) < 0)
break;

waited = true;
- schedule();
+ wait_woken(&vcpu_block_wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
}

preempt_disable();
--
2.38.1.584.g0f3c55d4c2-goog
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