[pve-devel] [RFC/PATCH v2 qemu 2/3] PVE-Backup: ensure jobs in di_list are referenced

[Fabian Ebner <f.ebner@proxmox.com>]

Ensures that qmp_backup_cancel doesn't pick a job that's already been
freed. With unlucky timings it seems possible that:
1. job_exit -> job_completed -> job_finalize_single starts
2. pvebackup_co_complete_stream gets spawned in completion callback
3. job finalize_single finishes -> job's refcount hits zero -> job is
   freed
4. qmp_backup_cancel comes in and locks backup_state.backup_mutex
   before pvebackup_co_complete_stream can remove the job from the
   di_list
5. qmp_backup_cancel will pick a job that's already been freed

Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>
---

New in v2.

 pve-backup.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/pve-backup.c b/pve-backup.c
index dfaf4c93f8..3cede98b1d 100644
--- a/pve-backup.c
+++ b/pve-backup.c
@@ -314,6 +314,11 @@ static void coroutine_fn pvebackup_co_complete_stream(void *opaque)
         }
     }
 
+    if (di->job) {
+        job_unref(&di->job->job);
+        di->job = NULL;
+    }
+
     // remove self from job list
     backup_state.di_list = g_list_remove(backup_state.di_list, di);
 
@@ -497,6 +502,9 @@ static void create_backup_jobs_bh(void *opaque) {
         aio_context_release(aio_context);
 
         di->job = job;
+        if (job) {
+            job_ref(&job->job);
+        }
 
         if (!job || local_err) {
             error_setg(errp, "backup_job_create failed: %s",
@@ -531,6 +539,11 @@ static void create_backup_jobs_bh(void *opaque) {
                 aio_context_release(ctx);
                 canceled = true;
             }
+
+            if (di->job) {
+                job_unref(&di->job->job);
+                di->job = NULL;
+            }
         }
     }
 
-- 
2.30.2