On 24.11.21 07:43, Emanuele Giuseppe Esposito wrote:
We want to be sure that the functions that write the child and
parent list of a bs are under BQL and drain.
BQL prevents from concurrent writings from the GS API, while
drains protect from I/O.
TODO: drains are missing in some functions using this assert.
Therefore a proper assertion will fail. Because adding drains
requires additional discussions, they will be added in future
series.
Signed-off-by: Emanuele Giuseppe Esposito <eespo...@redhat.com>
---
include/block/block_int-global-state.h | 10 +++++++++-
block.c | 4 ++++
block/io.c | 11 +++++++++++
3 files changed, 24 insertions(+), 1 deletion(-)
diff --git a/include/block/block_int-global-state.h
b/include/block/block_int-global-state.h
index a1b7d0579d..fa96e8b449 100644
--- a/include/block/block_int-global-state.h
+++ b/include/block/block_int-global-state.h
@@ -312,4 +312,12 @@ void bdrv_remove_aio_context_notifier(BlockDriverState *bs,
*/
void bdrv_drain_all_end_quiesce(BlockDriverState *bs);
-#endif /* BLOCK_INT_GLOBAL_STATE*/
This looks like it should be squashed into patch 7, sorry I missed this
in v4...
(Rest of this patch looks good to me, for the record – and while I’m at
it, for patches I didn’t reply to so far, I planned to send an R-b
later. But then there’s things like patches 2/3 looking good to me, but
it turned out in my review for patch 4 that bdrv_lock_medium() is used
in an I/O path, so I can’t really send an R-b now anymore...)
Hanna
+/**
+ * Make sure that the function is running under both drain and BQL.
+ * The latter protects from concurrent writings
+ * from the GS API, while the former prevents concurrent reads
+ * from I/O.
+ */
+void assert_bdrv_graph_writable(BlockDriverState *bs);
+
+#endif /* BLOCK_INT_GLOBAL_STATE */
diff --git a/block.c b/block.c
index 198ec636ff..522a273140 100644
--- a/block.c
+++ b/block.c
@@ -1416,6 +1416,7 @@ static void bdrv_child_cb_attach(BdrvChild *child)
{
BlockDriverState *bs = child->opaque;
+ assert_bdrv_graph_writable(bs);
QLIST_INSERT_HEAD(&bs->children, child, next);
if (child->role & BDRV_CHILD_COW) {
@@ -1435,6 +1436,7 @@ static void bdrv_child_cb_detach(BdrvChild *child)
bdrv_unapply_subtree_drain(child, bs);
+ assert_bdrv_graph_writable(bs);
QLIST_REMOVE(child, next);
}
@@ -2818,6 +2820,7 @@ static void bdrv_replace_child_noperm(BdrvChild **childp,
if (child->klass->detach) {
child->klass->detach(child);
}
+ assert_bdrv_graph_writable(old_bs);
QLIST_REMOVE(child, next_parent);
}
@@ -2827,6 +2830,7 @@ static void bdrv_replace_child_noperm(BdrvChild **childp,
}
if (new_bs) {
+ assert_bdrv_graph_writable(new_bs);
QLIST_INSERT_HEAD(&new_bs->parents, child, next_parent);
/*
diff --git a/block/io.c b/block/io.c
index cb095deeec..3be08cad29 100644
--- a/block/io.c
+++ b/block/io.c
@@ -734,6 +734,17 @@ void bdrv_drain_all(void)
bdrv_drain_all_end();
}
+void assert_bdrv_graph_writable(BlockDriverState *bs)
+{
+ /*
+ * TODO: this function is incomplete. Because the users of this
+ * assert lack the necessary drains, check only for BQL.
+ * Once the necessary drains are added,
+ * assert also for qatomic_read(&bs->quiesce_counter) > 0
+ */
+ assert(qemu_in_main_thread());
+}
+
/**
* Remove an active request from the tracked requests list
*