From f1bb53c690051994f5a2c43ee900f9e335bd019c Mon Sep 17 00:00:00 2001
From: Frans Kaashoek <kaashoek@mit.edu>
Date: Tue, 30 Jul 2019 08:13:03 -0400
Subject: [PATCH] The driver should free descriptors, not interrupt handler. 
 This avoids handler freeing descriptors before driver sees that the request
 has completed.

---
 kernel/virtio_disk.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/virtio_disk.c b/kernel/virtio_disk.c
index df4473d..9ebe695 100644
--- a/kernel/virtio_disk.c
+++ b/kernel/virtio_disk.c
@@ -239,6 +239,9 @@ virtio_disk_rw(struct buf *b, int write)
     sleep(b, &vdisk_lock);
   }
 
+  info[idx[0]].b = 0;
+  free_chain(idx[0]);
+
   release(&vdisk_lock);
 }
 
@@ -256,9 +259,6 @@ virtio_disk_intr()
     info[id].status = 1;
     wakeup(info[id].b);
 
-    info[id].b = 0;
-    free_chain(id);
-
     used_idx = (used_idx + 1) % NUM;
   }