[PATCH v3 2/6] virtio_ccw: always take irq_lock in the classic interrupt handler

[Karl Mehltretter]

virtio_ccw_int_handler() takes vcdev->irq_lock around its
vring_interrupt() calls only when VIRTIO_HARDEN_NOTIFICATION is enabled.

The virtio shutdown path calls synchronize_cbs() even when notification
hardening is disabled. virtio_reset_device() now does so after the
transport reset too.

For classic interrupts, synchronize_cbs() takes vcdev->irq_lock for
writing, but the interrupt handler does not take the matching read
lock in that configuration. synchronize_cbs() can return while a
callback is still running.

Take the read lock unconditionally so the write side can synchronize
with the callbacks.

Fixes: 8bd2fa086a04 ("virtio: break and reset virtio devices on device_shutdown()")
Assisted-by: LLM
Signed-off-by: Karl Mehltretter <kmehltretter@xxxxxxxxx>
---
 drivers/s390/virtio/virtio_ccw.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c
index b90299205698..552d77998012 100644
--- a/drivers/s390/virtio/virtio_ccw.c
+++ b/drivers/s390/virtio/virtio_ccw.c
@@ -1204,13 +1204,11 @@ static void virtio_ccw_int_handler(struct ccw_device *cdev,
 			vcdev->err = -EIO;
 	}
 	virtio_ccw_check_activity(vcdev, activity);
-#ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
 	/*
 	 * Paired with virtio_ccw_synchronize_cbs() and interrupts are
 	 * disabled here.
 	 */
 	read_lock(&vcdev->irq_lock);
-#endif
 	for_each_set_bit(i, indicators(vcdev),
 			 sizeof(*indicators(vcdev)) * BITS_PER_BYTE) {
 		/* The bit clear must happen before the vring kick. */
@@ -1219,9 +1217,7 @@ static void virtio_ccw_int_handler(struct ccw_device *cdev,
 		vq = virtio_ccw_vq_by_ind(vcdev, i);
 		vring_interrupt(0, vq);
 	}
-#ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
 	read_unlock(&vcdev->irq_lock);
-#endif
 	if (test_bit(0, indicators2(vcdev))) {
 		virtio_config_changed(&vcdev->vdev);
 		clear_bit(0, indicators2(vcdev));
-- 
2.39.5 (Apple Git-154)