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block: introduce assert_bdrv_graph_writable

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We want to be sure that the functions that write the child and
parent list of a bs are under BQL and drain.

BQL prevents from concurrent writings from the GS API, while
drains protect from I/O.

TODO: drains are missing in some functions using this assert.
Therefore a proper assertion will fail. Because adding drains
requires additional discussions, they will be added in future
series.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Message-Id: <20220303151616.325444-15-eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Emanuele Giuseppe Esposito 2022-03-03 10:15:59 -05:00 committed by Kevin Wolf
parent 967d7905d1
commit 696bf4c78c
2 changed files with 21 additions and 0 deletions
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4
block.c
View File

@ -1420,6 +1420,7 @@ static void bdrv_child_cb_attach(BdrvChild *child)
{
BlockDriverState *bs = child->opaque;
assert_bdrv_graph_writable(bs);
QLIST_INSERT_HEAD(&bs->children, child, next);
if (child->role & BDRV_CHILD_COW) {
@ -1439,6 +1440,7 @@ static void bdrv_child_cb_detach(BdrvChild *child)
bdrv_unapply_subtree_drain(child, bs);
assert_bdrv_graph_writable(bs);
QLIST_REMOVE(child, next);
}
@ -2829,6 +2831,7 @@ static void bdrv_replace_child_noperm(BdrvChild **childp,
if (child->klass->detach) {
child->klass->detach(child);
}
assert_bdrv_graph_writable(old_bs);
QLIST_REMOVE(child, next_parent);
}
@ -2838,6 +2841,7 @@ static void bdrv_replace_child_noperm(BdrvChild **childp,
}
if (new_bs) {
assert_bdrv_graph_writable(new_bs);
QLIST_INSERT_HEAD(&new_bs->parents, child, next_parent);
/*

17
include/block/block_int-global-state.h
View File

@ -309,4 +309,21 @@ void bdrv_remove_aio_context_notifier(BlockDriverState *bs,
*/
void bdrv_drain_all_end_quiesce(BlockDriverState *bs);
/**
* Make sure that the function is running under both drain and BQL.
* The latter protects from concurrent writings
* from the GS API, while the former prevents concurrent reads
* from I/O.
*/
static inline void assert_bdrv_graph_writable(BlockDriverState *bs)
{
/*
* TODO: this function is incomplete. Because the users of this
* assert lack the necessary drains, check only for BQL.
* Once the necessary drains are added,
* assert also for qatomic_read(&bs->quiesce_counter) > 0
*/
assert(qemu_in_main_thread());
}
#endif /* BLOCK_INT_GLOBAL_STATE */