[PATCH RFC 08/12] Documentation: KVM: Add example for kvm->srcu in relation to mutex/lock

[Ackerley Tng via B4 Relay]

From: Ackerley Tng <ackerleytng@xxxxxxxxxx>

Add example of where vcpu->mutex and kvm->slots_lock are held while calling
synchronize_srcu(&kvm->srcu) to concretely show where the synchronization
primitives overlap.

Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
---
 Documentation/virt/kvm/locking.rst | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/Documentation/virt/kvm/locking.rst b/Documentation/virt/kvm/locking.rst
index 437dbfa0030b9..f12664443e913 100644
--- a/Documentation/virt/kvm/locking.rst
+++ b/Documentation/virt/kvm/locking.rst
@@ -35,9 +35,12 @@ The acquisition orders for mutexes are as follows:
 For SRCU:
 
 - ``synchronize_srcu(&kvm->srcu)`` is called inside critical sections
-  for vcpu->mutex and kvm->slots_lock.  These locks _cannot_ be taken
-  inside a kvm->srcu read-side critical section; that is, the
-  following is broken::
+  for vcpu->mutex and kvm->slots_lock.  (For example, when there is a
+  ``KVM_REQ_APICV_UPDATE`` request, ``vcpu->mutex`` is held in
+  ``kvm_vcpu_ioctl()``, and then when the memslots get updated,
+  ``kvm->slots_lock`` is taken.)  These locks _cannot_ be taken inside
+  a kvm->srcu read-side critical section; that is, the following is
+  broken::
 
       srcu_read_lock(&kvm->srcu);
       mutex_lock(&kvm->slots_lock);

-- 
2.54.0.823.g6e5bcc1fc9-goog