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Blame SOURCES/kvm-block-Drain-recursively-with-a-single-BDRV_POLL_WHIL.patch

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From 013989ed30ff32eedbb1a6767f0c38c85150f951 Mon Sep 17 00:00:00 2001
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From: Kevin Wolf <kwolf@redhat.com>
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Date: Wed, 10 Oct 2018 20:21:39 +0100
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Subject: [PATCH 13/49] block: Drain recursively with a single
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 BDRV_POLL_WHILE()
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RH-Author: Kevin Wolf <kwolf@redhat.com>
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Message-id: <20181010202213.7372-1-kwolf@redhat.com>
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Patchwork-id: 82590
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O-Subject: [RHEL-8 qemu-kvm PATCH 10/44] block: Drain recursively with a single BDRV_POLL_WHILE()
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Bugzilla: 1637976
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RH-Acked-by: Max Reitz <mreitz@redhat.com>
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RH-Acked-by: John Snow <jsnow@redhat.com>
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RH-Acked-by: Thomas Huth <thuth@redhat.com>
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Anything can happen inside BDRV_POLL_WHILE(), including graph
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changes that may interfere with its callers (e.g. child list iteration
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in recursive callers of bdrv_do_drained_begin).
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Switch to a single BDRV_POLL_WHILE() call for the whole subtree at the
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end of bdrv_do_drained_begin() to avoid such effects. The recursion
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happens now inside the loop condition. As the graph can only change
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between bdrv_drain_poll() calls, but not inside of it, doing the
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recursion here is safe.
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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(cherry picked from commit fe4f0614ef9e361dae12012d3c400657444836cf)
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
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---
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 block.c               |  2 +-
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 block/io.c            | 63 ++++++++++++++++++++++++++++++++++++---------------
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 include/block/block.h |  9 +++++---
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 3 files changed, 52 insertions(+), 22 deletions(-)
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diff --git a/block.c b/block.c
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index 0d9698a..9afaf26 100644
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--- a/block.c
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+++ b/block.c
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@@ -824,7 +824,7 @@ static void bdrv_child_cb_drained_begin(BdrvChild *child)
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 static bool bdrv_child_cb_drained_poll(BdrvChild *child)
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 {
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     BlockDriverState *bs = child->opaque;
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-    return bdrv_drain_poll(bs, NULL);
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+    return bdrv_drain_poll(bs, false, NULL);
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 }
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 static void bdrv_child_cb_drained_end(BdrvChild *child)
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diff --git a/block/io.c b/block/io.c
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index a0e3461..442ded1 100644
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--- a/block/io.c
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+++ b/block/io.c
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@@ -164,6 +164,7 @@ typedef struct {
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     bool done;
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     bool begin;
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     bool recursive;
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+    bool poll;
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     BdrvChild *parent;
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 } BdrvCoDrainData;
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@@ -199,27 +200,42 @@ static void bdrv_drain_invoke(BlockDriverState *bs, bool begin)
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 }
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 /* Returns true if BDRV_POLL_WHILE() should go into a blocking aio_poll() */
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-bool bdrv_drain_poll(BlockDriverState *bs, BdrvChild *ignore_parent)
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+bool bdrv_drain_poll(BlockDriverState *bs, bool recursive,
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+                     BdrvChild *ignore_parent)
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 {
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+    BdrvChild *child, *next;
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+
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     if (bdrv_parent_drained_poll(bs, ignore_parent)) {
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         return true;
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     }
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-    return atomic_read(&bs->in_flight);
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+    if (atomic_read(&bs->in_flight)) {
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+        return true;
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+    }
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+
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+    if (recursive) {
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+        QLIST_FOREACH_SAFE(child, &bs->children, next, next) {
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+            if (bdrv_drain_poll(child->bs, recursive, child)) {
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+                return true;
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+            }
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+        }
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+    }
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+
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+    return false;
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 }
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-static bool bdrv_drain_poll_top_level(BlockDriverState *bs,
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+static bool bdrv_drain_poll_top_level(BlockDriverState *bs, bool recursive,
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                                       BdrvChild *ignore_parent)
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 {
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     /* Execute pending BHs first and check everything else only after the BHs
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      * have executed. */
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     while (aio_poll(bs->aio_context, false));
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-    return bdrv_drain_poll(bs, ignore_parent);
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+    return bdrv_drain_poll(bs, recursive, ignore_parent);
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 }
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 static void bdrv_do_drained_begin(BlockDriverState *bs, bool recursive,
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-                                  BdrvChild *parent);
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+                                  BdrvChild *parent, bool poll);
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 static void bdrv_do_drained_end(BlockDriverState *bs, bool recursive,
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                                 BdrvChild *parent);
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@@ -231,7 +247,7 @@ static void bdrv_co_drain_bh_cb(void *opaque)
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     bdrv_dec_in_flight(bs);
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     if (data->begin) {
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-        bdrv_do_drained_begin(bs, data->recursive, data->parent);
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+        bdrv_do_drained_begin(bs, data->recursive, data->parent, data->poll);
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     } else {
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         bdrv_do_drained_end(bs, data->recursive, data->parent);
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     }
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@@ -242,7 +258,7 @@ static void bdrv_co_drain_bh_cb(void *opaque)
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 static void coroutine_fn bdrv_co_yield_to_drain(BlockDriverState *bs,
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                                                 bool begin, bool recursive,
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-                                                BdrvChild *parent)
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+                                                BdrvChild *parent, bool poll)
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 {
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     BdrvCoDrainData data;
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@@ -257,6 +273,7 @@ static void coroutine_fn bdrv_co_yield_to_drain(BlockDriverState *bs,
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         .begin = begin,
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         .recursive = recursive,
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         .parent = parent,
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+        .poll = poll,
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     };
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     bdrv_inc_in_flight(bs);
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     aio_bh_schedule_oneshot(bdrv_get_aio_context(bs),
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@@ -269,12 +286,12 @@ static void coroutine_fn bdrv_co_yield_to_drain(BlockDriverState *bs,
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 }
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 void bdrv_do_drained_begin(BlockDriverState *bs, bool recursive,
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-                           BdrvChild *parent)
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+                           BdrvChild *parent, bool poll)
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 {
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     BdrvChild *child, *next;
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     if (qemu_in_coroutine()) {
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-        bdrv_co_yield_to_drain(bs, true, recursive, parent);
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+        bdrv_co_yield_to_drain(bs, true, recursive, parent, poll);
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         return;
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     }
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@@ -286,25 +303,35 @@ void bdrv_do_drained_begin(BlockDriverState *bs, bool recursive,
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     bdrv_parent_drained_begin(bs, parent);
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     bdrv_drain_invoke(bs, true);
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-    /* Wait for drained requests to finish */
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-    BDRV_POLL_WHILE(bs, bdrv_drain_poll_top_level(bs, parent));
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-
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     if (recursive) {
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         bs->recursive_quiesce_counter++;
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         QLIST_FOREACH_SAFE(child, &bs->children, next, next) {
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-            bdrv_do_drained_begin(child->bs, true, child);
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+            bdrv_do_drained_begin(child->bs, true, child, false);
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         }
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     }
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+
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+    /*
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+     * Wait for drained requests to finish.
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+     *
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+     * Calling BDRV_POLL_WHILE() only once for the top-level node is okay: The
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+     * call is needed so things in this AioContext can make progress even
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+     * though we don't return to the main AioContext loop - this automatically
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+     * includes other nodes in the same AioContext and therefore all child
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+     * nodes.
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+     */
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+    if (poll) {
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+        BDRV_POLL_WHILE(bs, bdrv_drain_poll_top_level(bs, recursive, parent));
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+    }
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 }
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 void bdrv_drained_begin(BlockDriverState *bs)
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 {
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-    bdrv_do_drained_begin(bs, false, NULL);
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+    bdrv_do_drained_begin(bs, false, NULL, true);
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 }
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 void bdrv_subtree_drained_begin(BlockDriverState *bs)
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 {
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-    bdrv_do_drained_begin(bs, true, NULL);
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+    bdrv_do_drained_begin(bs, true, NULL, true);
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 }
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 void bdrv_do_drained_end(BlockDriverState *bs, bool recursive,
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@@ -314,7 +341,7 @@ void bdrv_do_drained_end(BlockDriverState *bs, bool recursive,
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     int old_quiesce_counter;
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     if (qemu_in_coroutine()) {
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-        bdrv_co_yield_to_drain(bs, false, recursive, parent);
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+        bdrv_co_yield_to_drain(bs, false, recursive, parent, false);
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         return;
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     }
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     assert(bs->quiesce_counter > 0);
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@@ -350,7 +377,7 @@ void bdrv_apply_subtree_drain(BdrvChild *child, BlockDriverState *new_parent)
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     int i;
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     for (i = 0; i < new_parent->recursive_quiesce_counter; i++) {
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-        bdrv_do_drained_begin(child->bs, true, child);
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+        bdrv_do_drained_begin(child->bs, true, child, true);
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     }
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 }
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@@ -420,7 +447,7 @@ void bdrv_drain_all_begin(void)
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         AioContext *aio_context = bdrv_get_aio_context(bs);
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         aio_context_acquire(aio_context);
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-        bdrv_do_drained_begin(bs, true, NULL);
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+        bdrv_do_drained_begin(bs, true, NULL, true);
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         aio_context_release(aio_context);
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     }
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diff --git a/include/block/block.h b/include/block/block.h
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index 8c91d4c..2bbea7c 100644
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--- a/include/block/block.h
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+++ b/include/block/block.h
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@@ -598,10 +598,13 @@ void bdrv_parent_drained_end(BlockDriverState *bs, BdrvChild *ignore);
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 /**
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  * bdrv_drain_poll:
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  *
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- * Poll for pending requests in @bs and its parents (except for
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- * @ignore_parent). This is part of bdrv_drained_begin.
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+ * Poll for pending requests in @bs, its parents (except for @ignore_parent),
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+ * and if @recursive is true its children as well.
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+ *
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+ * This is part of bdrv_drained_begin.
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  */
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-bool bdrv_drain_poll(BlockDriverState *bs, BdrvChild *ignore_parent);
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+bool bdrv_drain_poll(BlockDriverState *bs, bool recursive,
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+                     BdrvChild *ignore_parent);
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 /**
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  * bdrv_drained_begin:
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-- 
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1.8.3.1
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