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block: move drain outside of bdrv_root_attach_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 function bdrv_root_attach_child() runs under the graph lock, so it
is not allowed to drain. It is called by:
1. blk_insert_bs(), where a drained section is introduced.
2. block_job_add_bdrv(), which holds the graph lock itself.

block_job_add_bdrv() is called by:
1. mirror_start_job()
2. stream_start()
3. commit_start()
4. backup_job_create()
5. block_job_create()
6. In the test_blockjob_common_drain_node() unit test

In all callers, a drained section is introduced.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20250530151125.955508-13-f.ebner@proxmox.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Fiona Ebner
2025-06-04 18:16:34 +02:00
committed by Kevin Wolf
parent e66dbda11e
commit ffdcd081f5
9 changed files with 27 additions and 2 deletions
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block/commit.c
+4
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@@ -392,6 +392,7 @@ void commit_start(const char *job_id, BlockDriverState *bs,
* this is the responsibility of the interface (i.e. whoever calls
* commit_start()).
*/
bdrv_drain_all_begin();
bdrv_graph_wrlock();
s->base_overlay = bdrv_find_overlay(top, base);
assert(s->base_overlay);
@@ -424,18 +425,21 @@ void commit_start(const char *job_id, BlockDriverState *bs,
iter_shared_perms, errp);
if (ret < 0) {
bdrv_graph_wrunlock();
bdrv_drain_all_end();
goto fail;
}
}
if (bdrv_freeze_backing_chain(commit_top_bs, base, errp) < 0) {
bdrv_graph_wrunlock();
bdrv_drain_all_end();
goto fail;
}
s->chain_frozen = true;
ret = block_job_add_bdrv(&s->common, "base", base, 0, BLK_PERM_ALL, errp);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
if (ret < 0) {
goto fail;