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From: Kevin Wolf <kwolf@redhat.com>
To: qemu-block@nongnu.org
Date: Fri, 22 Dec 2017 16:18:19 +0100
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Subject: [Qemu-devel] [PULL v3 08/35] block: Unify order in drain functions
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Drain requests are propagated to child nodes, parent nodes and directly
to the AioContext. The order in which this happened was different
between all combinations of drain/drain_all and begin/end.
The correct order is to keep children only drained when their parents
are also drained. This means that at the start of a drained section, the
AioContext needs to be drained first, the parents second and only then
the children. The correct order for the end of a drained section is the
opposite.
This patch changes the three other functions to follow the example of
bdrv_drained_begin(), which is the only one that got it right.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
---
block/io.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/block/io.c b/block/io.c
index 5fdb92a15e..1e92d2e5b2 100644
--- a/block/io.c
+++ b/block/io.c
@@ -277,6 +277,7 @@ void bdrv_drained_begin(BlockDriverState *bs)
return;
}
=20
+ /* Stop things in parent-to-child order */
if (atomic_fetch_inc(&bs->quiesce_counter) =3D=3D 0) {
aio_disable_external(bdrv_get_aio_context(bs));
bdrv_parent_drained_begin(bs);
@@ -297,8 +298,9 @@ void bdrv_drained_end(BlockDriverState *bs)
return;
}
=20
- bdrv_parent_drained_end(bs);
+ /* Re-enable things in child-to-parent order */
bdrv_drain_invoke(bs, false);
+ bdrv_parent_drained_end(bs);
aio_enable_external(bdrv_get_aio_context(bs));
}
=20
@@ -351,9 +353,10 @@ void bdrv_drain_all_begin(void)
for (bs =3D bdrv_first(&it); bs; bs =3D bdrv_next(&it)) {
AioContext *aio_context =3D bdrv_get_aio_context(bs);
=20
+ /* Stop things in parent-to-child order */
aio_context_acquire(aio_context);
- bdrv_parent_drained_begin(bs);
aio_disable_external(aio_context);
+ bdrv_parent_drained_begin(bs);
bdrv_drain_invoke(bs, true);
aio_context_release(aio_context);
=20
@@ -395,10 +398,11 @@ void bdrv_drain_all_end(void)
for (bs =3D bdrv_first(&it); bs; bs =3D bdrv_next(&it)) {
AioContext *aio_context =3D bdrv_get_aio_context(bs);
=20
+ /* Re-enable things in child-to-parent order */
aio_context_acquire(aio_context);
- aio_enable_external(aio_context);
- bdrv_parent_drained_end(bs);
bdrv_drain_invoke(bs, false);
+ bdrv_parent_drained_end(bs);
+ aio_enable_external(aio_context);
aio_context_release(aio_context);
}
=20
--=20
2.13.6