Revert "mirror: Don't let an operation wait for itself"

This reverts commit 7e6c4ff7.

The fix was incomplete as it only protected against requests waiting for
themselves, but not against requests waiting for each other. We need a
different solution.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Message-Id: <20200326153628.4869-2-kwolf@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/mirror.c

@@ -283,14 +283,11 @@ static int mirror_cow_align(MirrorBlockJob *s, int64_t *offset,
 }
 
 static inline void coroutine_fn
-mirror_wait_for_any_operation(MirrorBlockJob *s, MirrorOp *self, bool active)
+mirror_wait_for_any_operation(MirrorBlockJob *s, bool active)
 {
     MirrorOp *op;
 
     QTAILQ_FOREACH(op, &s->ops_in_flight, next) {
-        if (self == op) {
-            continue;
-        }
         /* Do not wait on pseudo ops, because it may in turn wait on
          * some other operation to start, which may in fact be the
          * caller of this function.  Since there is only one pseudo op
@@ -305,10 +302,10 @@ mirror_wait_for_any_operation(MirrorBlockJob *s, MirrorOp *self, bool active)
 }
 
 static inline void coroutine_fn
-mirror_wait_for_free_in_flight_slot(MirrorBlockJob *s, MirrorOp *self)
+mirror_wait_for_free_in_flight_slot(MirrorBlockJob *s)
 {
     /* Only non-active operations use up in-flight slots */
-    mirror_wait_for_any_operation(s, self, false);
+    mirror_wait_for_any_operation(s, false);
 }
 
 /* Perform a mirror copy operation.
@@ -351,7 +348,7 @@ static void coroutine_fn mirror_co_read(void *opaque)
 
     while (s->buf_free_count < nb_chunks) {
         trace_mirror_yield_in_flight(s, op->offset, s->in_flight);
-        mirror_wait_for_free_in_flight_slot(s, op);
+        mirror_wait_for_free_in_flight_slot(s);
     }
 
     /* Now make a QEMUIOVector taking enough granularity-sized chunks
@@ -558,7 +555,7 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
 
         while (s->in_flight >= MAX_IN_FLIGHT) {
             trace_mirror_yield_in_flight(s, offset, s->in_flight);
-            mirror_wait_for_free_in_flight_slot(s, pseudo_op);
+            mirror_wait_for_free_in_flight_slot(s);
         }
 
         if (s->ret < 0) {
@@ -612,7 +609,7 @@ static void mirror_free_init(MirrorBlockJob *s)
 static void coroutine_fn mirror_wait_for_all_io(MirrorBlockJob *s)
 {
     while (s->in_flight > 0) {
-        mirror_wait_for_free_in_flight_slot(s, NULL);
+        mirror_wait_for_free_in_flight_slot(s);
     }
 }
 
@@ -810,7 +807,7 @@ static int coroutine_fn mirror_dirty_init(MirrorBlockJob *s)
             if (s->in_flight >= MAX_IN_FLIGHT) {
                 trace_mirror_yield(s, UINT64_MAX, s->buf_free_count,
                                    s->in_flight);
-                mirror_wait_for_free_in_flight_slot(s, NULL);
+                mirror_wait_for_free_in_flight_slot(s);
                 continue;
             }
 
@@ -963,7 +960,7 @@ static int coroutine_fn mirror_run(Job *job, Error **errp)
         /* Do not start passive operations while there are active
          * writes in progress */
         while (s->in_active_write_counter) {
-            mirror_wait_for_any_operation(s, NULL, true);
+            mirror_wait_for_any_operation(s, true);
         }
 
         if (s->ret < 0) {
@@ -989,7 +986,7 @@ static int coroutine_fn mirror_run(Job *job, Error **errp)
             if (s->in_flight >= MAX_IN_FLIGHT || s->buf_free_count == 0 ||
                 (cnt == 0 && s->in_flight > 0)) {
                 trace_mirror_yield(s, cnt, s->buf_free_count, s->in_flight);
-                mirror_wait_for_free_in_flight_slot(s, NULL);
+                mirror_wait_for_free_in_flight_slot(s);
                 continue;
             } else if (cnt != 0) {
                 delay_ns = mirror_iteration(s);