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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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

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;

4
block/blklogwrites.c
View File

@ -281,9 +281,11 @@ static int blk_log_writes_open(BlockDriverState *bs, QDict *options, int flags,
ret = 0;
fail_log:
if (ret < 0) {
bdrv_drain_all_begin();
bdrv_graph_wrlock();
bdrv_unref_child(bs, s->log_file);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
s->log_file = NULL;
qemu_mutex_destroy(&s->mutex);
}
@ -296,10 +298,12 @@ static void blk_log_writes_close(BlockDriverState *bs)
{
BDRVBlkLogWritesState *s = bs->opaque;
bdrv_drain_all_begin();
bdrv_graph_wrlock();
bdrv_unref_child(bs, s->log_file);
s->log_file = NULL;
bdrv_graph_wrunlock();
bdrv_drain_all_end();
qemu_mutex_destroy(&s->mutex);
}

2
block/blkverify.c
View File

@ -151,10 +151,12 @@ static void blkverify_close(BlockDriverState *bs)
{
BDRVBlkverifyState *s = bs->opaque;
bdrv_drain_all_begin();
bdrv_graph_wrlock();
bdrv_unref_child(bs, s->test_file);
s->test_file = NULL;
bdrv_graph_wrunlock();
bdrv_drain_all_end();
}
static int64_t coroutine_fn GRAPH_RDLOCK

2
block/block-backend.c
View File

@ -889,9 +889,11 @@ void blk_remove_bs(BlockBackend *blk)
root = blk->root;
blk->root = NULL;
bdrv_drain_all_begin();
bdrv_graph_wrlock();
bdrv_root_unref_child(root);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
}
/*

4
block/qcow2.c
View File

@ -1895,7 +1895,9 @@ qcow2_do_open(BlockDriverState *bs, QDict *options, int flags,
g_free(s->image_data_file);
if (open_data_file && has_data_file(bs)) {
bdrv_graph_co_rdunlock();
bdrv_drain_all_begin();
bdrv_co_unref_child(bs, s->data_file);
bdrv_drain_all_end();
bdrv_graph_co_rdlock();
s->data_file = NULL;
}
@ -2821,9 +2823,11 @@ qcow2_do_close(BlockDriverState *bs, bool close_data_file)
if (close_data_file && has_data_file(bs)) {
GLOBAL_STATE_CODE();
bdrv_graph_rdunlock_main_loop();
bdrv_drain_all_begin();
bdrv_graph_wrlock();
bdrv_unref_child(bs, s->data_file);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
s->data_file = NULL;
bdrv_graph_rdlock_main_loop();
}

6
block/quorum.c
View File

@ -1037,6 +1037,7 @@ static int quorum_open(BlockDriverState *bs, QDict *options, int flags,
close_exit:
/* cleanup on error */
bdrv_drain_all_begin();
bdrv_graph_wrlock();
for (i = 0; i < s->num_children; i++) {
if (!opened[i]) {
@ -1045,6 +1046,7 @@ close_exit:
bdrv_unref_child(bs, s->children[i]);
}
bdrv_graph_wrunlock();
bdrv_drain_all_end();
g_free(s->children);
g_free(opened);
exit:
@ -1057,11 +1059,13 @@ static void quorum_close(BlockDriverState *bs)
BDRVQuorumState *s = bs->opaque;
int i;
bdrv_drain_all_begin();
bdrv_graph_wrlock();
for (i = 0; i < s->num_children; i++) {
bdrv_unref_child(bs, s->children[i]);
}
bdrv_graph_wrunlock();
bdrv_drain_all_end();
g_free(s->children);
}
@ -1143,7 +1147,9 @@ quorum_del_child(BlockDriverState *bs, BdrvChild *child, Error **errp)
(s->num_children - i - 1) * sizeof(BdrvChild *));
s->children = g_renew(BdrvChild *, s->children, --s->num_children);
bdrv_drain_all_begin();
bdrv_unref_child(bs, child);
bdrv_drain_all_end();
quorum_refresh_flags(bs);
}

2
block/replication.c
View File

@ -656,12 +656,14 @@ static void replication_done(void *opaque, int ret)
if (ret == 0) {
s->stage = BLOCK_REPLICATION_DONE;
bdrv_drain_all_begin();
bdrv_graph_wrlock();
bdrv_unref_child(bs, s->secondary_disk);
s->secondary_disk = NULL;
bdrv_unref_child(bs, s->hidden_disk);
s->hidden_disk = NULL;
bdrv_graph_wrunlock();
bdrv_drain_all_end();
s->error = 0;
} else {

2
block/snapshot.c
View File

@ -291,9 +291,11 @@ int bdrv_snapshot_goto(BlockDriverState *bs,
}
/* .bdrv_open() will re-attach it */
bdrv_drain_all_begin();
bdrv_graph_wrlock();
bdrv_unref_child(bs, fallback);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
ret = bdrv_snapshot_goto(fallback_bs, snapshot_id, errp);
memset(bs->opaque, 0, drv->instance_size);

10
block/vmdk.c
View File

@ -271,6 +271,7 @@ static void vmdk_free_extents(BlockDriverState *bs)
BDRVVmdkState *s = bs->opaque;
VmdkExtent *e;
bdrv_drain_all_begin();
bdrv_graph_wrlock();
for (i = 0; i < s->num_extents; i++) {
e = &s->extents[i];
@ -283,6 +284,7 @@ static void vmdk_free_extents(BlockDriverState *bs)
}
}
bdrv_graph_wrunlock();
bdrv_drain_all_end();
g_free(s->extents);
}
@ -1247,9 +1249,11 @@ vmdk_parse_extents(const char *desc, BlockDriverState *bs, QDict *options,
0, 0, 0, 0, 0, &extent, errp);
if (ret < 0) {
bdrv_graph_rdunlock_main_loop();
bdrv_drain_all_begin();
bdrv_graph_wrlock();
bdrv_unref_child(bs, extent_file);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
bdrv_graph_rdlock_main_loop();
goto out;
}
@ -1266,9 +1270,11 @@ vmdk_parse_extents(const char *desc, BlockDriverState *bs, QDict *options,
g_free(buf);
if (ret) {
bdrv_graph_rdunlock_main_loop();
bdrv_drain_all_begin();
bdrv_graph_wrlock();
bdrv_unref_child(bs, extent_file);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
bdrv_graph_rdlock_main_loop();
goto out;
}
@ -1277,9 +1283,11 @@ vmdk_parse_extents(const char *desc, BlockDriverState *bs, QDict *options,
ret = vmdk_open_se_sparse(bs, extent_file, bs->open_flags, errp);
if (ret) {
bdrv_graph_rdunlock_main_loop();
bdrv_drain_all_begin();
bdrv_graph_wrlock();
bdrv_unref_child(bs, extent_file);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
bdrv_graph_rdlock_main_loop();
goto out;
}
@ -1287,9 +1295,11 @@ vmdk_parse_extents(const char *desc, BlockDriverState *bs, QDict *options,
} else {
error_setg(errp, "Unsupported extent type '%s'", type);
bdrv_graph_rdunlock_main_loop();
bdrv_drain_all_begin();
bdrv_graph_wrlock();
bdrv_unref_child(bs, extent_file);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
bdrv_graph_rdlock_main_loop();
ret = -ENOTSUP;
goto out;

2
blockjob.c
View File

@ -198,6 +198,7 @@ void block_job_remove_all_bdrv(BlockJob *job)
* one to make sure that such a concurrent access does not attempt
* to process an already freed BdrvChild.
*/
bdrv_drain_all_begin();
bdrv_graph_wrlock();
while (job->nodes) {
GSList *l = job->nodes;
@ -211,6 +212,7 @@ void block_job_remove_all_bdrv(BlockJob *job)
g_slist_free_1(l);
}
bdrv_graph_wrunlock();
bdrv_drain_all_end();
}
bool block_job_has_bdrv(BlockJob *job, BlockDriverState *bs)

4
tests/unit/test-bdrv-drain.c
View File

@ -955,11 +955,13 @@ static void bdrv_test_top_close(BlockDriverState *bs)
{
BdrvChild *c, *next_c;
bdrv_drain_all_begin();
bdrv_graph_wrlock();
QLIST_FOREACH_SAFE(c, &bs->children, next, next_c) {
bdrv_unref_child(bs, c);
}
bdrv_graph_wrunlock();
bdrv_drain_all_end();
}
static int coroutine_fn GRAPH_RDLOCK
@ -1016,7 +1018,9 @@ static void coroutine_fn test_co_delete_by_drain(void *opaque)
bdrv_graph_co_rdlock();
QLIST_FOREACH_SAFE(c, &bs->children, next, next_c) {
bdrv_graph_co_rdunlock();
bdrv_drain_all_begin();
bdrv_co_unref_child(bs, c);
bdrv_drain_all_end();
bdrv_graph_co_rdlock();
}
bdrv_graph_co_rdunlock();