From: Fiona Ebner <f.eb...@proxmox.com>
This is part of resolving the deadlock mentioned in commit "block:
move draining out of bdrv_change_aio_context() and mark GRAPH_RDLOCK".
The quorum_add_child() callback runs under the graph lock, so it is
not allowed to drain. It is only called as the .bdrv_add_child()
callback, which is only called in the bdrv_add_child() function, which
also runs under the graph lock.
The bdrv_add_child() function is called by qmp_x_blockdev_change(),
where a drained section is introduced.
Signed-off-by: Fiona Ebner <f.eb...@proxmox.com>
Message-ID: <20250530151125.955508-15-f.eb...@proxmox.com>
Reviewed-by: Kevin Wolf <kw...@redhat.com>
Signed-off-by: Kevin Wolf <kw...@redhat.com>
---
include/block/block_int-common.h | 7 +++++++
block.c | 10 ++++++++--
block/quorum.c | 2 --
blockdev.c | 2 ++
4 files changed, 17 insertions(+), 4 deletions(-)
diff --git a/include/block/block_int-common.h b/include/block/block_int-common.h
index 168f703fa1..f9e742f812 100644
--- a/include/block/block_int-common.h
+++ b/include/block/block_int-common.h
@@ -396,6 +396,13 @@ struct BlockDriver {
int GRAPH_RDLOCK_PTR (*bdrv_probe_geometry)(
BlockDriverState *bs, HDGeometry *geo);
+ /**
+ * Hot add a BDS's child. Used in combination with bdrv_del_child, so the
+ * user can take a child offline when it is broken and take a new child
+ * online.
+ *
+ * All block nodes must be drained.
+ */
void GRAPH_WRLOCK_PTR (*bdrv_add_child)(
BlockDriverState *parent, BlockDriverState *child, Error **errp);
diff --git a/block.c b/block.c
index 6fc87aa318..f6c2f7e208 100644
--- a/block.c
+++ b/block.c
@@ -8220,8 +8220,10 @@ char *bdrv_dirname(BlockDriverState *bs, Error **errp)
}
/*
- * Hot add/remove a BDS's child. So the user can take a child offline when
- * it is broken and take a new child online
+ * Hot add a BDS's child. Used in combination with bdrv_del_child, so the user
+ * can take a child offline when it is broken and take a new child online.
+ *
+ * All block nodes must be drained.
*/
void bdrv_add_child(BlockDriverState *parent_bs, BlockDriverState *child_bs,
Error **errp)
@@ -8261,6 +8263,10 @@ void bdrv_add_child(BlockDriverState *parent_bs,
BlockDriverState *child_bs,
parent_bs->drv->bdrv_add_child(parent_bs, child_bs, errp);
}
+/*
+ * Hot remove a BDS's child. Used in combination with bdrv_add_child, so the
+ * user can take a child offline when it is broken and take a new child online.
+ */
void bdrv_del_child(BlockDriverState *parent_bs, BdrvChild *child, Error
**errp)
{
BdrvChild *tmp;
diff --git a/block/quorum.c b/block/quorum.c
index ea17b0ec13..ed8ce801ee 100644
--- a/block/quorum.c
+++ b/block/quorum.c
@@ -1096,10 +1096,8 @@ quorum_add_child(BlockDriverState *bs, BlockDriverState
*child_bs, Error **errp)
/* We can safely add the child now */
bdrv_ref(child_bs);
- bdrv_drain_all_begin();
child = bdrv_attach_child(bs, child_bs, indexstr, &child_of_bds,
BDRV_CHILD_DATA, errp);
- bdrv_drain_all_end();
if (child == NULL) {
s->next_child_index--;
return;
diff --git a/blockdev.c b/blockdev.c
index 750beba41f..bd5ca77619 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -3531,6 +3531,7 @@ void qmp_x_blockdev_change(const char *parent, const char
*child,
BlockDriverState *parent_bs, *new_bs = NULL;
BdrvChild *p_child;
+ bdrv_drain_all_begin();
bdrv_graph_wrlock();
parent_bs = bdrv_lookup_bs(parent, parent, errp);
@@ -3568,6 +3569,7 @@ void qmp_x_blockdev_change(const char *parent, const char
*child,
out:
bdrv_graph_wrunlock();
+ bdrv_drain_all_end();
}
BlockJobInfoList *qmp_query_block_jobs(Error **errp)
--
2.49.0
