From 72f0fcad0938bba82537e78753e242d53f3f2583 Mon Sep 17 00:00:00 2001

From: Kevin Wolf <kwolf@redhat.com>

Date: Fri, 14 Sep 2018 10:55:10 +0200

Subject: [PATCH 19/49] block: Don't poll in parent drain callbacks

RH-Author: Kevin Wolf <kwolf@redhat.com>

Message-id: <20180914105540.18077-13-kwolf@redhat.com>

Patchwork-id: 82164

O-Subject: [RHV-7.6 qemu-kvm-rhev PATCH 12/42] block: Don't poll in parent drain callbacks

Bugzilla: 1601212

RH-Acked-by: John Snow <jsnow@redhat.com>

RH-Acked-by: Max Reitz <mreitz@redhat.com>

RH-Acked-by: Fam Zheng <famz@redhat.com>

bdrv_do_drained_begin() is only safe if we have a single

BDRV_POLL_WHILE() after quiescing all affected nodes. We cannot allow

that parent callbacks introduce a nested polling loop that could cause

graph changes while we're traversing the graph.

Split off bdrv_do_drained_begin_quiesce(), which only quiesces a single

node without waiting for its requests to complete. These requests will

be waited for in the BDRV_POLL_WHILE() call down the call chain.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

(cherry picked from commit dcf94a23b1add0f856db51e9ff5ba0774e096076)

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>

---

 block.c               |  2 +-

 block/io.c            | 24 ++++++++++++++++--------

 include/block/block.h |  9 +++++++++

 3 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/block.c b/block.c

index 9afaf26..5a50de6 100644

--- a/block.c

+++ b/block.c

@@ -818,7 +818,7 @@ static char *bdrv_child_get_parent_desc(BdrvChild *c)

 static void bdrv_child_cb_drained_begin(BdrvChild *child)

 {

     BlockDriverState *bs = child->opaque;

-    bdrv_drained_begin(bs);

+    bdrv_do_drained_begin_quiesce(bs, NULL);

 }

 static bool bdrv_child_cb_drained_poll(BdrvChild *child)

diff --git a/block/io.c b/block/io.c

index 442ded1..9c41ff9 100644

--- a/block/io.c

+++ b/block/io.c

@@ -285,15 +285,10 @@ static void coroutine_fn bdrv_co_yield_to_drain(BlockDriverState *bs,

     assert(data.done);

 }

-void bdrv_do_drained_begin(BlockDriverState *bs, bool recursive,

-                           BdrvChild *parent, bool poll)

+void bdrv_do_drained_begin_quiesce(BlockDriverState *bs,

+                                   BdrvChild *parent)

 {

-    BdrvChild *child, *next;

-

-    if (qemu_in_coroutine()) {

-        bdrv_co_yield_to_drain(bs, true, recursive, parent, poll);

-        return;

-    }

+    assert(!qemu_in_coroutine());

     /* Stop things in parent-to-child order */

     if (atomic_fetch_inc(&bs->quiesce_counter) == 0) {

@@ -302,6 +297,19 @@ void bdrv_do_drained_begin(BlockDriverState *bs, bool recursive,

     bdrv_parent_drained_begin(bs, parent);

     bdrv_drain_invoke(bs, true);

+}

+

+static void bdrv_do_drained_begin(BlockDriverState *bs, bool recursive,

+                                  BdrvChild *parent, bool poll)

+{

+    BdrvChild *child, *next;

+

+    if (qemu_in_coroutine()) {

+        bdrv_co_yield_to_drain(bs, true, recursive, parent, poll);

+        return;

+    }

+

+    bdrv_do_drained_begin_quiesce(bs, parent);

     if (recursive) {

         bs->recursive_quiesce_counter++;

diff --git a/include/block/block.h b/include/block/block.h

index 2bbea7c..43f29b5 100644

--- a/include/block/block.h

+++ b/include/block/block.h

@@ -619,6 +619,15 @@ bool bdrv_drain_poll(BlockDriverState *bs, bool recursive,

 void bdrv_drained_begin(BlockDriverState *bs);

 /**

+ * bdrv_do_drained_begin_quiesce:

+ *

+ * Quiesces a BDS like bdrv_drained_begin(), but does not wait for already

+ * running requests to complete.

+ */

+void bdrv_do_drained_begin_quiesce(BlockDriverState *bs,

+                                   BdrvChild *parent);

+

+/**

  * Like bdrv_drained_begin, but recursively begins a quiesced section for

  * exclusive access to all child nodes as well.

  */

-- 

1.8.3.1