2011-03-06 11:03:37

by Michael S. Tsirkin

Subject: [PATCH] kvm: improve comment on rcu use in irqfd_deassign

The RCU use in kvm_irqfd_deassign is tricky: we have rcu_assign_pointer
but no synchronize_rcu: synchronize_rcu is done by kvm_irq_routing_update
which we share a spinlock with.

Fix up a comment in an attempt to make this clearer.

Signed-off-by: Michael S. Tsirkin <[email protected]>
---
virt/kvm/eventfd.c | 5 +++--
1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 2ca4535..3656849 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -313,8 +313,9 @@ kvm_irqfd_deassign(struct kvm *kvm, int fd, int gsi)
if (irqfd->eventfd == eventfd && irqfd->gsi == gsi) {
/*
* This rcu_assign_pointer is needed for when
- * another thread calls kvm_irqfd_update before
- * we flush workqueue below.
+ * another thread calls kvm_irq_routing_update before
+ * we flush workqueue below (we synchronize with
+ * kvm_irq_routing_update using irqfds.lock).
* It is paired with synchronize_rcu done by caller
* of that function.
*/
--
1.7.3.2.91.g446ac

2011-03-06 12:36:27

by Avi Kivity

Subject: Re: [PATCH] kvm: improve comment on rcu use in irqfd_deassign

On 03/06/2011 01:03 PM, Michael S. Tsirkin wrote:
> The RCU use in kvm_irqfd_deassign is tricky: we have rcu_assign_pointer
> but no synchronize_rcu: synchronize_rcu is done by kvm_irq_routing_update
> which we share a spinlock with.
>
> Fix up a comment in an attempt to make this clearer.

Applied, thanks.

--
error compiling committee.c: too many arguments to function