[PATCH 03/10] mshv: Fix missing lock in mshv_irqfd_deassign

[Stanislav Kinsburskii]

mshv_irqfd_deactivate() and the hlist traversal of pt_irqfds_list
require pt->pt_irqfds_lock to be held, but mshv_irqfd_deassign()
omits it. This races with the EPOLLHUP path in mshv_irqfd_wakeup(),
which does take the lock before calling mshv_irqfd_deactivate().

Add the missing spin_lock_irq/spin_unlock_irq around the list
traversal, matching the pattern in mshv_irqfd_release().

Fixes: 621191d709b14 ("Drivers: hv: Introduce mshv_root module to expose 
/dev/mshv to VMMs")
Signed-off-by: Stanislav Kinsburskii <skinsburs...@linux.microsoft.com>
---
 drivers/hv/mshv_eventfd.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/hv/mshv_eventfd.c b/drivers/hv/mshv_eventfd.c
index 90959f639dc32..704c229ee3b19 100644
--- a/drivers/hv/mshv_eventfd.c
+++ b/drivers/hv/mshv_eventfd.c
@@ -541,13 +541,14 @@ static int mshv_irqfd_deassign(struct mshv_partition *pt,
        if (IS_ERR(eventfd))
                return PTR_ERR(eventfd);
 
+       spin_lock_irq(&pt->pt_irqfds_lock);
        hlist_for_each_entry_safe(irqfd, n, &pt->pt_irqfds_list,
                                  irqfd_hnode) {
                if (irqfd->irqfd_eventfd_ctx == eventfd &&
                    irqfd->irqfd_irqnum == args->gsi)
-
                        mshv_irqfd_deactivate(irqfd);
        }
+       spin_unlock_irq(&pt->pt_irqfds_lock);
 
        eventfd_ctx_put(eventfd);