From 013989ed30ff32eedbb1a6767f0c38c85150f951 Mon Sep 17 00:00:00 2001

From: Kevin Wolf <kwolf@redhat.com>

Date: Wed, 10 Oct 2018 20:21:39 +0100

Subject: [PATCH 13/49] block: Drain recursively with a single

 BDRV_POLL_WHILE()

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

Message-id: <20181010202213.7372-1-kwolf@redhat.com>

Patchwork-id: 82590

O-Subject: [RHEL-8 qemu-kvm PATCH 10/44] block: Drain recursively with a single BDRV_POLL_WHILE()

Bugzilla: 1637976

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

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

RH-Acked-by: Thomas Huth <thuth@redhat.com>

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 <kwolf@redhat.com>

(cherry picked from commit fe4f0614ef9e361dae12012d3c400657444836cf)

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

Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>

---

 block.c               |  2 +-

 block/io.c            | 63 ++++++++++++++++++++++++++++++++++++---------------

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

 3 files changed, 52 insertions(+), 22 deletions(-)

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

index 0d9698a..9afaf26 100644

--- a/block.c

+++ b/block.c

@@ -824,7 +824,7 @@ 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, NULL);

+    return bdrv_drain_poll(bs, false, NULL);

 }

 static void bdrv_child_cb_drained_end(BdrvChild *child)

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

index a0e3461..442ded1 100644

--- a/block/io.c

+++ b/block/io.c

@@ -164,6 +164,7 @@ typedef struct {

     bool done;

     bool begin;

     bool recursive;

+    bool poll;

     BdrvChild *parent;

 } BdrvCoDrainData;

@@ -199,27 +200,42 @@ 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, BdrvChild *ignore_parent)

+bool bdrv_drain_poll(BlockDriverState *bs, bool recursive,

+                     BdrvChild *ignore_parent)

 {

+    BdrvChild *child, *next;

+

     if (bdrv_parent_drained_poll(bs, ignore_parent)) {

         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, recursive, child)) {

+                return true;

+            }

+        }

+    }

+

+    return false;

 }

-static bool bdrv_drain_poll_top_level(BlockDriverState *bs,

+static bool bdrv_drain_poll_top_level(BlockDriverState *bs, bool recursive,

                                       BdrvChild *ignore_parent)

 {

     /* Execute pending BHs first and check everything else only after the BHs

      * have executed. */

     while (aio_poll(bs->aio_context, false));

-    return bdrv_drain_poll(bs, ignore_parent);

+    return bdrv_drain_poll(bs, recursive, ignore_parent);

 }

 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);

@@ -231,7 +247,7 @@ 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);

     }

@@ -242,7 +258,7 @@ 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;

@@ -257,6 +273,7 @@ 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),

@@ -269,12 +286,12 @@ 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;

     }

@@ -286,25 +303,35 @@ 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_top_level(bs, parent));

-

     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_top_level(bs, recursive, parent));

+    }

 }

 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,

@@ -314,7 +341,7 @@ 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);

@@ -350,7 +377,7 @@ 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);

     }

 }

@@ -420,7 +447,7 @@ 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);

     }

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

index 8c91d4c..2bbea7c 100644

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

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

@@ -598,10 +598,13 @@ void bdrv_parent_drained_end(BlockDriverState *bs, BdrvChild *ignore);

 /**

  * bdrv_drain_poll:

  *

- * Poll for pending requests in @bs and its parents (except for

- * @ignore_parent). This is part of bdrv_drained_begin.

+ * Poll for pending requests in @bs, its parents (except for @ignore_parent),

+ * and if @recursive is true its children as well.

+ *

+ * This is part of bdrv_drained_begin.

  */

-bool bdrv_drain_poll(BlockDriverState *bs, BdrvChild *ignore_parent);

+bool bdrv_drain_poll(BlockDriverState *bs, bool recursive,

+                     BdrvChild *ignore_parent);

 /**

  * bdrv_drained_begin:

-- 

1.8.3.1