Anything can happen inside BDRV_POLL_WHILE(), including graph
changes that may interfere with its callers (e.g. child list iteration
in recursive callers of bdrv_do_drained_begin).
Switch to a single BDRV_POLL_WHILE() call for the whole subtree at the
end of bdrv_do_drained_begin() to avoid such effects. The recursion
happens now inside the loop condition. As the graph can only change
between bdrv_drain_poll() calls, but not inside of it, doing the
recursion here is safe.
Signed-off-by: Kevin Wolf <kw...@redhat.com>
---
include/block/block.h | 2 +-
block.c | 2 +-
block/io.c | 58 +++++++++++++++++++++++++++++++++++++--------------
3 files changed, 44 insertions(+), 18 deletions(-)
diff --git a/include/block/block.h b/include/block/block.h
index 23dee3c114..91bf3b4e36 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -563,7 +563,7 @@ void bdrv_parent_drained_end(BlockDriverState *bs,
BdrvChild *ignore);
*
* Poll for pending requests in @bs. This is part of bdrv_drained_begin.
*/
-bool bdrv_drain_poll(BlockDriverState *bs, bool top_level);
+bool bdrv_drain_poll(BlockDriverState *bs, bool top_level, bool recursive);
/**
* bdrv_drained_begin:
diff --git a/block.c b/block.c
index 462287bdfb..9fe39ac8c1 100644
--- a/block.c
+++ b/block.c
@@ -823,7 +823,7 @@ static void bdrv_child_cb_drained_begin(BdrvChild *child)
static bool bdrv_child_cb_drained_poll(BdrvChild *child)
{
BlockDriverState *bs = child->opaque;
- return bdrv_drain_poll(bs, false);
+ return bdrv_drain_poll(bs, false, false);
}
static void bdrv_child_cb_drained_end(BdrvChild *child)
diff --git a/block/io.c b/block/io.c
index f24f39c278..1287630c58 100644
--- a/block/io.c
+++ b/block/io.c
@@ -161,6 +161,7 @@ typedef struct {
bool done;
bool begin;
bool recursive;
+ bool poll;
BdrvChild *parent;
} BdrvCoDrainData;
@@ -196,8 +197,10 @@ static void bdrv_drain_invoke(BlockDriverState *bs, bool
begin)
}
/* Returns true if BDRV_POLL_WHILE() should go into a blocking aio_poll() */
-bool bdrv_drain_poll(BlockDriverState *bs, bool top_level)
+bool bdrv_drain_poll(BlockDriverState *bs, bool top_level, bool recursive)
{
+ BdrvChild *child, *next;
+
/* Execute pending BHs first and check everything else only after the BHs
* have executed. */
if (top_level) {
@@ -208,11 +211,23 @@ bool bdrv_drain_poll(BlockDriverState *bs, bool top_level)
return true;
}
- return atomic_read(&bs->in_flight);
+ if (atomic_read(&bs->in_flight)) {
+ return true;
+ }
+
+ if (recursive) {
+ QLIST_FOREACH_SAFE(child, &bs->children, next, next) {
+ if (bdrv_drain_poll(child->bs, false, recursive)) {
+ return true;
+ }
+ }
+ }
+
+ return false;
}
static void bdrv_do_drained_begin(BlockDriverState *bs, bool recursive,
- BdrvChild *parent);
+ BdrvChild *parent, bool poll);
static void bdrv_do_drained_end(BlockDriverState *bs, bool recursive,
BdrvChild *parent);
@@ -224,7 +239,7 @@ static void bdrv_co_drain_bh_cb(void *opaque)
bdrv_dec_in_flight(bs);
if (data->begin) {
- bdrv_do_drained_begin(bs, data->recursive, data->parent);
+ bdrv_do_drained_begin(bs, data->recursive, data->parent, data->poll);
} else {
bdrv_do_drained_end(bs, data->recursive, data->parent);
}
@@ -235,7 +250,7 @@ static void bdrv_co_drain_bh_cb(void *opaque)
static void coroutine_fn bdrv_co_yield_to_drain(BlockDriverState *bs,
bool begin, bool recursive,
- BdrvChild *parent)
+ BdrvChild *parent, bool poll)
{
BdrvCoDrainData data;
@@ -250,6 +265,7 @@ static void coroutine_fn
bdrv_co_yield_to_drain(BlockDriverState *bs,
.begin = begin,
.recursive = recursive,
.parent = parent,
+ .poll = poll,
};
bdrv_inc_in_flight(bs);
aio_bh_schedule_oneshot(bdrv_get_aio_context(bs),
@@ -262,12 +278,12 @@ static void coroutine_fn
bdrv_co_yield_to_drain(BlockDriverState *bs,
}
void bdrv_do_drained_begin(BlockDriverState *bs, bool recursive,
- BdrvChild *parent)
+ BdrvChild *parent, bool poll)
{
BdrvChild *child, *next;
if (qemu_in_coroutine()) {
- bdrv_co_yield_to_drain(bs, true, recursive, parent);
+ bdrv_co_yield_to_drain(bs, true, recursive, parent, poll);
return;
}
@@ -279,25 +295,35 @@ void bdrv_do_drained_begin(BlockDriverState *bs, bool
recursive,
bdrv_parent_drained_begin(bs, parent);
bdrv_drain_invoke(bs, true);
- /* Wait for drained requests to finish */
- BDRV_POLL_WHILE(bs, bdrv_drain_poll(bs, true));
-
if (recursive) {
bs->recursive_quiesce_counter++;
QLIST_FOREACH_SAFE(child, &bs->children, next, next) {
- bdrv_do_drained_begin(child->bs, true, child);
+ bdrv_do_drained_begin(child->bs, true, child, false);
}
}
+
+ /*
+ * Wait for drained requests to finish.
+ *
+ * Calling BDRV_POLL_WHILE() only once for the top-level node is okay: The
+ * call is needed so things in this AioContext can make progress even
+ * though we don't return to the main AioContext loop - this automatically
+ * includes other nodes in the same AioContext and therefore all child
+ * nodes.
+ */
+ if (poll) {
+ BDRV_POLL_WHILE(bs, bdrv_drain_poll(bs, true, recursive));
+ }
}
void bdrv_drained_begin(BlockDriverState *bs)
{
- bdrv_do_drained_begin(bs, false, NULL);
+ bdrv_do_drained_begin(bs, false, NULL, true);
}
void bdrv_subtree_drained_begin(BlockDriverState *bs)
{
- bdrv_do_drained_begin(bs, true, NULL);
+ bdrv_do_drained_begin(bs, true, NULL, true);
}
void bdrv_do_drained_end(BlockDriverState *bs, bool recursive,
@@ -307,7 +333,7 @@ void bdrv_do_drained_end(BlockDriverState *bs, bool
recursive,
int old_quiesce_counter;
if (qemu_in_coroutine()) {
- bdrv_co_yield_to_drain(bs, false, recursive, parent);
+ bdrv_co_yield_to_drain(bs, false, recursive, parent, false);
return;
}
assert(bs->quiesce_counter > 0);
@@ -343,7 +369,7 @@ void bdrv_apply_subtree_drain(BdrvChild *child,
BlockDriverState *new_parent)
int i;
for (i = 0; i < new_parent->recursive_quiesce_counter; i++) {
- bdrv_do_drained_begin(child->bs, true, child);
+ bdrv_do_drained_begin(child->bs, true, child, true);
}
}
@@ -413,7 +439,7 @@ void bdrv_drain_all_begin(void)
AioContext *aio_context = bdrv_get_aio_context(bs);
aio_context_acquire(aio_context);
- bdrv_do_drained_begin(bs, true, NULL);
+ bdrv_do_drained_begin(bs, true, NULL, true);
aio_context_release(aio_context);
}
--
2.13.6
