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block: move drain outside of bdrv_root_unref_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".

bdrv_root_unref_child() is called by:
1. blk_remove_bs(), where a drained section is introduced.
2. bdrv_unref_child(), which runs under the graph lock, so the drain
   will be moved further up to its callers.
3. block_job_remove_all_bdrv(), where a drained section is introduced.

For all callers of bdrv_unref_child() and its generated
bdrv_co_unref_child() coroutine variant, a drained section is
introduced, they are not explicilty listed here. The caller
quorum_del_child() holds the graph lock, so it is not actually allowed
to drain. This will be addressed in the next commit.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Message-ID: <20250530151125.955508-16-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 17:10:52 +02:00 • committed by Kevin Wolf
parent 0414930d3a
commit b13f546545
11 changed files with 52 additions and 4 deletions
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18
block.c
View file

@ -1721,12 +1721,14 @@ bdrv_open_driver(BlockDriverState *bs, BlockDriver *drv, const char *node_name,
open_failed:
bs->drv = NULL;
bdrv_drain_all_begin();
bdrv_graph_wrlock();
if (bs->file != NULL) {
bdrv_unref_child(bs, bs->file);
assert(!bs->file);
}
bdrv_graph_wrunlock();
bdrv_drain_all_end();
g_free(bs->opaque);
bs->opaque = NULL;
@ -3305,7 +3307,11 @@ out:
return ret < 0 ? NULL : child;
}
/* Callers must ensure that child->frozen is false. */
/*
* Callers must ensure that child->frozen is false.
*
* All block nodes must be drained.
*/
void bdrv_root_unref_child(BdrvChild *child)
{
BlockDriverState *child_bs = child->bs;
@ -3326,10 +3332,8 @@ void bdrv_root_unref_child(BdrvChild *child)
* When the parent requiring a non-default AioContext is removed, the
* node moves back to the main AioContext
*/
bdrv_drain_all_begin();
bdrv_try_change_aio_context_locked(child_bs, qemu_get_aio_context(),
NULL, NULL);
bdrv_drain_all_end();
}
bdrv_schedule_unref(child_bs);
@ -3402,7 +3406,11 @@ bdrv_unset_inherits_from(BlockDriverState *root, BdrvChild *child,
}
}
/* Callers must ensure that child->frozen is false. */
/*
* Callers must ensure that child->frozen is false.
*
* All block nodes must be drained.
*/
void bdrv_unref_child(BlockDriverState *parent, BdrvChild *child)
{
GLOBAL_STATE_CODE();
@ -5172,6 +5180,7 @@ static void bdrv_close(BlockDriverState *bs)
bs->drv = NULL;
}
bdrv_drain_all_begin();
bdrv_graph_wrlock();
QLIST_FOREACH_SAFE(child, &bs->children, next, next) {
bdrv_unref_child(bs, child);
@ -5180,6 +5189,7 @@ static void bdrv_close(BlockDriverState *bs)
assert(!bs->backing);
assert(!bs->file);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
g_free(bs->opaque);
bs->opaque = NULL;