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block: move drain outside of quorum_add_child()

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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.ebner@proxmox.com>
Message-ID: <20250530151125.955508-15-f.ebner@proxmox.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Fiona Ebner 2025-05-30 17:10:51 +02:00 • committed by Kevin Wolf
parent 77f3965ba7
commit 0414930d3a
4 changed files with 17 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

10
block.c
View file

@ -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 * Hot add a BDS's child. Used in combination with bdrv_del_child, so the user
* it is broken and take a new child online * 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, void bdrv_add_child(BlockDriverState *parent_bs, BlockDriverState *child_bs,
Error **errp) 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); 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) void bdrv_del_child(BlockDriverState *parent_bs, BdrvChild *child, Error **errp)
{ {
BdrvChild *tmp; BdrvChild *tmp;

2
block/quorum.c
View file

@ -1096,10 +1096,8 @@ quorum_add_child(BlockDriverState *bs, BlockDriverState *child_bs, Error **errp)
/* We can safely add the child now */ /* We can safely add the child now */
bdrv_ref(child_bs); bdrv_ref(child_bs);
bdrv_drain_all_begin();
child = bdrv_attach_child(bs, child_bs, indexstr, &child_of_bds, child = bdrv_attach_child(bs, child_bs, indexstr, &child_of_bds,
BDRV_CHILD_DATA, errp); BDRV_CHILD_DATA, errp);
bdrv_drain_all_end();
if (child == NULL) { if (child == NULL) {
s->next_child_index--; s->next_child_index--;
return; return;

2
blockdev.c
View file

@ -3531,6 +3531,7 @@ void qmp_x_blockdev_change(const char *parent, const char *child,
BlockDriverState *parent_bs, *new_bs = NULL; BlockDriverState *parent_bs, *new_bs = NULL;
BdrvChild *p_child; BdrvChild *p_child;
bdrv_drain_all_begin();
bdrv_graph_wrlock(); bdrv_graph_wrlock();
parent_bs = bdrv_lookup_bs(parent, parent, errp); parent_bs = bdrv_lookup_bs(parent, parent, errp);
@ -3568,6 +3569,7 @@ void qmp_x_blockdev_change(const char *parent, const char *child,
out: out:
bdrv_graph_wrunlock(); bdrv_graph_wrunlock();
bdrv_drain_all_end();
} }
BlockJobInfoList *qmp_query_block_jobs(Error **errp) BlockJobInfoList *qmp_query_block_jobs(Error **errp)

7
include/block/block_int-common.h
View file

@ -396,6 +396,13 @@ struct BlockDriver {
int GRAPH_RDLOCK_PTR (*bdrv_probe_geometry)( int GRAPH_RDLOCK_PTR (*bdrv_probe_geometry)(
BlockDriverState *bs, HDGeometry *geo); 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)( void GRAPH_WRLOCK_PTR (*bdrv_add_child)(
BlockDriverState *parent, BlockDriverState *child, Error **errp); BlockDriverState *parent, BlockDriverState *child, Error **errp);