Merge remote-tracking branch 'remotes/famz/tags/block-pull-request' i…

…nto staging

# gpg: Signature made Tue 18 Apr 2017 15:58:32 BST
# gpg:                using RSA key 0xCA35624C6A9171C6
# gpg: Good signature from "Fam Zheng <famz@redhat.com>"
# gpg: WARNING: This key is not certified with sufficiently trusted signatures!
# gpg:          It is not certain that the signature belongs to the owner.
# Primary key fingerprint: 5003 7CB7 9706 0F76 F021  AD56 CA35 624C 6A91 71C6

* remotes/famz/tags/block-pull-request:
  block: Drain BH in bdrv_drained_begin
  block: Walk bs->children carefully in bdrv_drain_recurse

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

block/io.c

@@ -158,7 +158,7 @@ bool bdrv_requests_pending(BlockDriverState *bs)
 
 static bool bdrv_drain_recurse(BlockDriverState *bs)
 {
-    BdrvChild *child;
+    BdrvChild *child, *tmp;
     bool waited;
 
     waited = BDRV_POLL_WHILE(bs, atomic_read(&bs->in_flight) > 0);
@@ -167,8 +167,25 @@ static bool bdrv_drain_recurse(BlockDriverState *bs)
         bs->drv->bdrv_drain(bs);
     }
 
-    QLIST_FOREACH(child, &bs->children, next) {
-        waited |= bdrv_drain_recurse(child->bs);
+    QLIST_FOREACH_SAFE(child, &bs->children, next, tmp) {
+        BlockDriverState *bs = child->bs;
+        bool in_main_loop =
+            qemu_get_current_aio_context() == qemu_get_aio_context();
+        assert(bs->refcnt > 0);
+        if (in_main_loop) {
+            /* In case the recursive bdrv_drain_recurse processes a
+             * block_job_defer_to_main_loop BH and modifies the graph,
+             * let's hold a reference to bs until we are done.
+             *
+             * IOThread doesn't have such a BH, and it is not safe to call
+             * bdrv_unref without BQL, so skip doing it there.
+             */
+            bdrv_ref(bs);
+        }
+        waited |= bdrv_drain_recurse(bs);
+        if (in_main_loop) {
+            bdrv_unref(bs);
+        }
     }
 
     return waited;

include/block/block.h

@@ -381,12 +381,13 @@ void bdrv_drain_all(void);
 
 #define BDRV_POLL_WHILE(bs, cond) ({                       \
     bool waited_ = false;                                  \
+    bool busy_ = true;                                     \
     BlockDriverState *bs_ = (bs);                          \
     AioContext *ctx_ = bdrv_get_aio_context(bs_);          \
     if (aio_context_in_iothread(ctx_)) {                   \
-        while ((cond)) {                                   \
-            aio_poll(ctx_, true);                          \
-            waited_ = true;                                \
+        while ((cond) || busy_) {                          \
+            busy_ = aio_poll(ctx_, (cond));                \
+            waited_ |= !!(cond) | busy_;                   \
         }                                                  \
     } else {                                               \
         assert(qemu_get_current_aio_context() ==           \
@@ -398,11 +399,16 @@ void bdrv_drain_all(void);
          */                                                \
         assert(!bs_->wakeup);                              \
         bs_->wakeup = true;                                \
-        while ((cond)) {                                   \
-            aio_context_release(ctx_);                     \
-            aio_poll(qemu_get_aio_context(), true);        \
-            aio_context_acquire(ctx_);                     \
-            waited_ = true;                                \
+        while (busy_) {                                    \
+            if ((cond)) {                                  \
+                waited_ = busy_ = true;                    \
+                aio_context_release(ctx_);                 \
+                aio_poll(qemu_get_aio_context(), true);    \
+                aio_context_acquire(ctx_);                 \
+            } else {                                       \
+                busy_ = aio_poll(ctx_, false);             \
+                waited_ |= busy_;                          \
+            }                                              \
         }                                                  \
         bs_->wakeup = false;                               \
     }                                                      \