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block: move drain outside of bdrv_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_attach_child() runs under the graph lock, so it is
not allowed to drain. It is called by:
1. replication_start()
2. quorum_add_child()
3. bdrv_open_child_common()
4. Throughout test-bdrv-graph-mod.c and test-bdrv-drain.c unit tests.

In all callers, a drained section is introduced.

The function quorum_add_child() runs under the graph lock, so it is
not actually allowed to drain. This will be addressed by the following
commit.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20250530151125.955508-14-f.ebner@proxmox.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Fiona Ebner
2025-05-30 17:10:50 +02:00
committed by Kevin Wolf
parent ffdcd081f5
commit 77f3965ba7
5 changed files with 35 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files
block.c
+4 -2
View File
@@ -3269,6 +3269,8 @@ out:
*
* On failure NULL is returned, errp is set and the reference to
* child_bs is also dropped.
*
* All block nodes must be drained.
*/
BdrvChild *bdrv_attach_child(BlockDriverState *parent_bs,
BlockDriverState *child_bs,
@@ -3283,7 +3285,6 @@ BdrvChild *bdrv_attach_child(BlockDriverState *parent_bs,
GLOBAL_STATE_CODE();
bdrv_drain_all_begin();
child = bdrv_attach_child_noperm(parent_bs, child_bs, child_name,
child_class, child_role, tran, errp);
if (!child) {
@@ -3298,7 +3299,6 @@ BdrvChild *bdrv_attach_child(BlockDriverState *parent_bs,
out:
tran_finalize(tran, ret);
bdrv_drain_all_end();
bdrv_schedule_unref(child_bs);
@@ -3789,10 +3789,12 @@ static BdrvChild *bdrv_open_child_common(const char *filename,
return NULL;
}
bdrv_drain_all_begin();
bdrv_graph_wrlock();
child = bdrv_attach_child(parent, bs, bdref_key, child_class, child_role,
errp);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
return child;
}
block/quorum.c
+2
View File
@@ -1096,8 +1096,10 @@ 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;
block/replication.c
+5
View File
@@ -540,6 +540,7 @@ static void replication_start(ReplicationState *rs, ReplicationMode mode,
return;
}
bdrv_drain_all_begin();
bdrv_graph_wrlock();
bdrv_ref(hidden_disk->bs);
@@ -549,6 +550,7 @@ static void replication_start(ReplicationState *rs, ReplicationMode mode,
if (local_err) {
error_propagate(errp, local_err);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
return;
}
@@ -559,6 +561,7 @@ static void replication_start(ReplicationState *rs, ReplicationMode mode,
if (local_err) {
error_propagate(errp, local_err);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
return;
}
@@ -571,12 +574,14 @@ static void replication_start(ReplicationState *rs, ReplicationMode mode,
!check_top_bs(top_bs, bs)) {
error_setg(errp, "No top_bs or it is invalid");
bdrv_graph_wrunlock();
bdrv_drain_all_end();
reopen_backing_file(bs, false, NULL);
return;
}
bdrv_op_block_all(top_bs, s->blocker);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
s->backup_job = backup_job_create(
NULL, s->secondary_disk->bs, s->hidden_disk->bs,
tests/unit/test-bdrv-drain.c
+14
View File
@@ -1049,10 +1049,12 @@ static void do_test_delete_by_drain(bool detach_instead_of_delete,
null_bs = bdrv_open("null-co://", NULL, NULL, BDRV_O_RDWR | BDRV_O_PROTOCOL,
&error_abort);
bdrv_drain_all_begin();
bdrv_graph_wrlock();
bdrv_attach_child(bs, null_bs, "null-child", &child_of_bds,
BDRV_CHILD_DATA, &error_abort);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
/* This child will be the one to pass to requests through to, and
* it will stall until a drain occurs */
@@ -1060,21 +1062,25 @@ static void do_test_delete_by_drain(bool detach_instead_of_delete,
&error_abort);
child_bs->total_sectors = 65536 >> BDRV_SECTOR_BITS;
/* Takes our reference to child_bs */
bdrv_drain_all_begin();
bdrv_graph_wrlock();
tts->wait_child = bdrv_attach_child(bs, child_bs, "wait-child",
&child_of_bds,
BDRV_CHILD_DATA | BDRV_CHILD_PRIMARY,
&error_abort);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
/* This child is just there to be deleted
* (for detach_instead_of_delete == true) */
null_bs = bdrv_open("null-co://", NULL, NULL, BDRV_O_RDWR | BDRV_O_PROTOCOL,
&error_abort);
bdrv_drain_all_begin();
bdrv_graph_wrlock();
bdrv_attach_child(bs, null_bs, "null-child", &child_of_bds, BDRV_CHILD_DATA,
&error_abort);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
blk = blk_new(qemu_get_aio_context(), BLK_PERM_ALL, BLK_PERM_ALL);
blk_insert_bs(blk, bs, &error_abort);
@@ -1157,6 +1163,7 @@ static void no_coroutine_fn detach_indirect_bh(void *opaque)
bdrv_dec_in_flight(data->child_b->bs);
bdrv_drain_all_begin();
bdrv_graph_wrlock();
bdrv_unref_child(data->parent_b, data->child_b);
@@ -1165,6 +1172,7 @@ static void no_coroutine_fn detach_indirect_bh(void *opaque)
&child_of_bds, BDRV_CHILD_DATA,
&error_abort);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
}
static void coroutine_mixed_fn detach_by_parent_aio_cb(void *opaque, int ret)
@@ -1262,6 +1270,7 @@ static void TSA_NO_TSA test_detach_indirect(bool by_parent_cb)
/* Set child relationships */
bdrv_ref(b);
bdrv_ref(a);
bdrv_drain_all_begin();
bdrv_graph_wrlock();
child_b = bdrv_attach_child(parent_b, b, "PB-B", &child_of_bds,
BDRV_CHILD_DATA, &error_abort);
@@ -1273,6 +1282,7 @@ static void TSA_NO_TSA test_detach_indirect(bool by_parent_cb)
by_parent_cb ? &child_of_bds : &detach_by_driver_cb_class,
BDRV_CHILD_DATA, &error_abort);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
g_assert_cmpint(parent_a->refcnt, ==, 1);
g_assert_cmpint(parent_b->refcnt, ==, 1);
@@ -1685,6 +1695,7 @@ static void test_drop_intermediate_poll(void)
* Establish the chain last, so the chain links are the first
* elements in the BDS.parents lists
*/
bdrv_drain_all_begin();
bdrv_graph_wrlock();
for (i = 0; i < 3; i++) {
if (i) {
@@ -1694,6 +1705,7 @@ static void test_drop_intermediate_poll(void)
}
}
bdrv_graph_wrunlock();
bdrv_drain_all_end();
job = block_job_create("job", &test_simple_job_driver, NULL, job_node,
0, BLK_PERM_ALL, 0, 0, NULL, NULL, &error_abort);
@@ -1940,10 +1952,12 @@ static void do_test_replace_child_mid_drain(int old_drain_count,
new_child_bs->total_sectors = 1;
bdrv_ref(old_child_bs);
bdrv_drain_all_begin();
bdrv_graph_wrlock();
bdrv_attach_child(parent_bs, old_child_bs, "child", &child_of_bds,
BDRV_CHILD_COW, &error_abort);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
parent_s->setup_completed = true;
for (i = 0; i < old_drain_count; i++) {
tests/unit/test-bdrv-graph-mod.c
+10
View File
@@ -137,10 +137,12 @@ static void test_update_perm_tree(void)
blk_insert_bs(root, bs, &error_abort);
bdrv_drain_all_begin();
bdrv_graph_wrlock();
bdrv_attach_child(filter, bs, "child", &child_of_bds,
BDRV_CHILD_DATA, &error_abort);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
ret = bdrv_append(filter, bs, NULL);
g_assert_cmpint(ret, <, 0);
@@ -204,11 +206,13 @@ static void test_should_update_child(void)
bdrv_set_backing_hd(target, bs, &error_abort);
bdrv_drain_all_begin();
bdrv_graph_wrlock();
g_assert(target->backing->bs == bs);
bdrv_attach_child(filter, target, "target", &child_of_bds,
BDRV_CHILD_DATA, &error_abort);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
bdrv_append(filter, bs, &error_abort);
bdrv_graph_rdlock_main_loop();
@@ -244,6 +248,7 @@ static void test_parallel_exclusive_write(void)
bdrv_ref(base);
bdrv_ref(fl1);
bdrv_drain_all_begin();
bdrv_graph_wrlock();
bdrv_attach_child(top, fl1, "backing", &child_of_bds,
BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY,
@@ -257,6 +262,7 @@ static void test_parallel_exclusive_write(void)
bdrv_replace_node(fl1, fl2, &error_abort);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
bdrv_drained_end(fl2);
bdrv_drained_end(fl1);
@@ -363,6 +369,7 @@ static void test_parallel_perm_update(void)
*/
bdrv_ref(base);
bdrv_drain_all_begin();
bdrv_graph_wrlock();
bdrv_attach_child(top, ws, "file", &child_of_bds, BDRV_CHILD_DATA,
&error_abort);
@@ -377,6 +384,7 @@ static void test_parallel_perm_update(void)
BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY,
&error_abort);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
/* Select fl1 as first child to be active */
s->selected = c_fl1;
@@ -430,11 +438,13 @@ static void test_append_greedy_filter(void)
BlockDriverState *base = no_perm_node("base");
BlockDriverState *fl = exclusive_writer_node("fl1");
bdrv_drain_all_begin();
bdrv_graph_wrlock();
bdrv_attach_child(top, base, "backing", &child_of_bds,
BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY,
&error_abort);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
bdrv_append(fl, base, &error_abort);
bdrv_unref(fl);