qemu-kvm/kvm-block-Remove-drained_end_counter.patch

From 3009e49f242ab371ffad35bb29c2c26ddfac75d4 Mon Sep 17 00:00:00 2001
From: Kevin Wolf <kwolf@redhat.com>
Date: Fri, 18 Nov 2022 18:40:59 +0100
Subject: [PATCH 17/31] block: Remove drained_end_counter

RH-Author: Stefano Garzarella <sgarzare@redhat.com>
RH-MergeRequest: 135: block: Simplify drain to prevent QEMU from crashing during snapshot
RH-Bugzilla: 2155112
RH-Acked-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
RH-Acked-by: Hanna Czenczek <hreitz@redhat.com>
RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
RH-Commit: [5/16] 5589e3f05dece5394a05641f7f42096e8dc62bdb (sgarzarella/qemu-kvm-c-9-s)

drained_end_counter is unused now, nobody changes its value any more. It
can be removed.

In cases where we had two almost identical functions that only differed
in whether the caller passes drained_end_counter, or whether they would
poll for a local drained_end_counter to reach 0, these become a single
function.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Message-Id: <20221118174110.55183-5-kwolf@redhat.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit 2f65df6e16dea2d6e7212fa675f4779d9281e26f)
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
 block.c                          |  5 +-
 block/block-backend.c            |  4 +-
 block/io.c                       | 98 ++++++++------------------------
 blockjob.c                       |  2 +-
 include/block/block-io.h         | 24 --------
 include/block/block_int-common.h |  6 +-
 6 files changed, 30 insertions(+), 109 deletions(-)

diff --git a/block.c b/block.c
index 16a62a329c..7999fd08c5 100644
--- a/block.c
+++ b/block.c
@@ -1235,11 +1235,10 @@ static bool bdrv_child_cb_drained_poll(BdrvChild *child)
     return bdrv_drain_poll(bs, false, NULL, false);
 }
 
-static void bdrv_child_cb_drained_end(BdrvChild *child,
-                                      int *drained_end_counter)
+static void bdrv_child_cb_drained_end(BdrvChild *child)
 {
     BlockDriverState *bs = child->opaque;
-    bdrv_drained_end_no_poll(bs, drained_end_counter);
+    bdrv_drained_end(bs);
 }
 
 static int bdrv_child_cb_inactivate(BdrvChild *child)
diff --git a/block/block-backend.c b/block/block-backend.c
index d98a96ff37..feaf2181fa 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -129,7 +129,7 @@ static void blk_root_inherit_options(BdrvChildRole role, bool parent_is_format,
 }
 static void blk_root_drained_begin(BdrvChild *child);
 static bool blk_root_drained_poll(BdrvChild *child);
-static void blk_root_drained_end(BdrvChild *child, int *drained_end_counter);
+static void blk_root_drained_end(BdrvChild *child);
 
 static void blk_root_change_media(BdrvChild *child, bool load);
 static void blk_root_resize(BdrvChild *child);
@@ -2556,7 +2556,7 @@ static bool blk_root_drained_poll(BdrvChild *child)
     return busy || !!blk->in_flight;
 }
 
-static void blk_root_drained_end(BdrvChild *child, int *drained_end_counter)
+static void blk_root_drained_end(BdrvChild *child)
 {
     BlockBackend *blk = child->opaque;
     assert(blk->quiesce_counter);
diff --git a/block/io.c b/block/io.c
index c2ed4b2af9..f4ca62b034 100644
--- a/block/io.c
+++ b/block/io.c
@@ -58,28 +58,19 @@ static void bdrv_parent_drained_begin(BlockDriverState *bs, BdrvChild *ignore,
     }
 }
 
-static void bdrv_parent_drained_end_single_no_poll(BdrvChild *c,
-                                                   int *drained_end_counter)
+void bdrv_parent_drained_end_single(BdrvChild *c)
 {
+    IO_OR_GS_CODE();
+
     assert(c->parent_quiesce_counter > 0);
     c->parent_quiesce_counter--;
     if (c->klass->drained_end) {
-        c->klass->drained_end(c, drained_end_counter);
+        c->klass->drained_end(c);
     }
 }
 
-void bdrv_parent_drained_end_single(BdrvChild *c)
-{
-    int drained_end_counter = 0;
-    AioContext *ctx = bdrv_child_get_parent_aio_context(c);
-    IO_OR_GS_CODE();
-    bdrv_parent_drained_end_single_no_poll(c, &drained_end_counter);
-    AIO_WAIT_WHILE(ctx, qatomic_read(&drained_end_counter) > 0);
-}
-
 static void bdrv_parent_drained_end(BlockDriverState *bs, BdrvChild *ignore,
-                                    bool ignore_bds_parents,
-                                    int *drained_end_counter)
+                                    bool ignore_bds_parents)
 {
     BdrvChild *c;
 
@@ -87,7 +78,7 @@ static void bdrv_parent_drained_end(BlockDriverState *bs, BdrvChild *ignore,
         if (c == ignore || (ignore_bds_parents && c->klass->parent_is_bds)) {
             continue;
         }
-        bdrv_parent_drained_end_single_no_poll(c, drained_end_counter);
+        bdrv_parent_drained_end_single(c);
     }
 }
 
@@ -249,12 +240,10 @@ typedef struct {
     bool poll;
     BdrvChild *parent;
     bool ignore_bds_parents;
-    int *drained_end_counter;
 } BdrvCoDrainData;
 
 /* Recursively call BlockDriver.bdrv_drain_begin/end callbacks */
-static void bdrv_drain_invoke(BlockDriverState *bs, bool begin,
-                              int *drained_end_counter)
+static void bdrv_drain_invoke(BlockDriverState *bs, bool begin)
 {
     if (!bs->drv || (begin && !bs->drv->bdrv_drain_begin) ||
             (!begin && !bs->drv->bdrv_drain_end)) {
@@ -305,8 +294,7 @@ static void bdrv_do_drained_begin(BlockDriverState *bs, bool recursive,
                                   BdrvChild *parent, bool ignore_bds_parents,
                                   bool poll);
 static void bdrv_do_drained_end(BlockDriverState *bs, bool recursive,
-                                BdrvChild *parent, bool ignore_bds_parents,
-                                int *drained_end_counter);
+                                BdrvChild *parent, bool ignore_bds_parents);
 
 static void bdrv_co_drain_bh_cb(void *opaque)
 {
@@ -319,14 +307,12 @@ static void bdrv_co_drain_bh_cb(void *opaque)
         aio_context_acquire(ctx);
         bdrv_dec_in_flight(bs);
         if (data->begin) {
-            assert(!data->drained_end_counter);
             bdrv_do_drained_begin(bs, data->recursive, data->parent,
                                   data->ignore_bds_parents, data->poll);
         } else {
             assert(!data->poll);
             bdrv_do_drained_end(bs, data->recursive, data->parent,
-                                data->ignore_bds_parents,
-                                data->drained_end_counter);
+                                data->ignore_bds_parents);
         }
         aio_context_release(ctx);
     } else {
@@ -342,8 +328,7 @@ static void coroutine_fn bdrv_co_yield_to_drain(BlockDriverState *bs,
                                                 bool begin, bool recursive,
                                                 BdrvChild *parent,
                                                 bool ignore_bds_parents,
-                                                bool poll,
-                                                int *drained_end_counter)
+                                                bool poll)
 {
     BdrvCoDrainData data;
     Coroutine *self = qemu_coroutine_self();
@@ -363,7 +348,6 @@ static void coroutine_fn bdrv_co_yield_to_drain(BlockDriverState *bs,
         .parent = parent,
         .ignore_bds_parents = ignore_bds_parents,
         .poll = poll,
-        .drained_end_counter = drained_end_counter,
     };
 
     if (bs) {
@@ -406,7 +390,7 @@ void bdrv_do_drained_begin_quiesce(BlockDriverState *bs,
     }
 
     bdrv_parent_drained_begin(bs, parent, ignore_bds_parents);
-    bdrv_drain_invoke(bs, true, NULL);
+    bdrv_drain_invoke(bs, true);
 }
 
 static void bdrv_do_drained_begin(BlockDriverState *bs, bool recursive,
@@ -417,7 +401,7 @@ static void bdrv_do_drained_begin(BlockDriverState *bs, bool recursive,
 
     if (qemu_in_coroutine()) {
         bdrv_co_yield_to_drain(bs, true, recursive, parent, ignore_bds_parents,
-                               poll, NULL);
+                               poll);
         return;
     }
 
@@ -461,38 +445,24 @@ void bdrv_subtree_drained_begin(BlockDriverState *bs)
 
 /**
  * This function does not poll, nor must any of its recursively called
- * functions.  The *drained_end_counter pointee will be incremented
- * once for every background operation scheduled, and decremented once
- * the operation settles.  Therefore, the pointer must remain valid
- * until the pointee reaches 0.  That implies that whoever sets up the
- * pointee has to poll until it is 0.
- *
- * We use atomic operations to access *drained_end_counter, because
- * (1) when called from bdrv_set_aio_context_ignore(), the subgraph of
- *     @bs may contain nodes in different AioContexts,
- * (2) bdrv_drain_all_end() uses the same counter for all nodes,
- *     regardless of which AioContext they are in.
+ * functions.
  */
 static void bdrv_do_drained_end(BlockDriverState *bs, bool recursive,
-                                BdrvChild *parent, bool ignore_bds_parents,
-                                int *drained_end_counter)
+                                BdrvChild *parent, bool ignore_bds_parents)
 {
     BdrvChild *child;
     int old_quiesce_counter;
 
-    assert(drained_end_counter != NULL);
-
     if (qemu_in_coroutine()) {
         bdrv_co_yield_to_drain(bs, false, recursive, parent, ignore_bds_parents,
-                               false, drained_end_counter);
+                               false);
         return;
     }
     assert(bs->quiesce_counter > 0);
 
     /* Re-enable things in child-to-parent order */
-    bdrv_drain_invoke(bs, false, drained_end_counter);
-    bdrv_parent_drained_end(bs, parent, ignore_bds_parents,
-                            drained_end_counter);
+    bdrv_drain_invoke(bs, false);
+    bdrv_parent_drained_end(bs, parent, ignore_bds_parents);
 
     old_quiesce_counter = qatomic_fetch_dec(&bs->quiesce_counter);
     if (old_quiesce_counter == 1) {
@@ -503,32 +473,21 @@ static void bdrv_do_drained_end(BlockDriverState *bs, bool recursive,
         assert(!ignore_bds_parents);
         bs->recursive_quiesce_counter--;
         QLIST_FOREACH(child, &bs->children, next) {
-            bdrv_do_drained_end(child->bs, true, child, ignore_bds_parents,
-                                drained_end_counter);
+            bdrv_do_drained_end(child->bs, true, child, ignore_bds_parents);
         }
     }
 }
 
 void bdrv_drained_end(BlockDriverState *bs)
 {
-    int drained_end_counter = 0;
     IO_OR_GS_CODE();
-    bdrv_do_drained_end(bs, false, NULL, false, &drained_end_counter);
-    BDRV_POLL_WHILE(bs, qatomic_read(&drained_end_counter) > 0);
-}
-
-void bdrv_drained_end_no_poll(BlockDriverState *bs, int *drained_end_counter)
-{
-    IO_CODE();
-    bdrv_do_drained_end(bs, false, NULL, false, drained_end_counter);
+    bdrv_do_drained_end(bs, false, NULL, false);
 }
 
 void bdrv_subtree_drained_end(BlockDriverState *bs)
 {
-    int drained_end_counter = 0;
     IO_OR_GS_CODE();
-    bdrv_do_drained_end(bs, true, NULL, false, &drained_end_counter);
-    BDRV_POLL_WHILE(bs, qatomic_read(&drained_end_counter) > 0);
+    bdrv_do_drained_end(bs, true, NULL, false);
 }
 
 void bdrv_apply_subtree_drain(BdrvChild *child, BlockDriverState *new_parent)
@@ -543,16 +502,12 @@ void bdrv_apply_subtree_drain(BdrvChild *child, BlockDriverState *new_parent)
 
 void bdrv_unapply_subtree_drain(BdrvChild *child, BlockDriverState *old_parent)
 {
-    int drained_end_counter = 0;
     int i;
     IO_OR_GS_CODE();
 
     for (i = 0; i < old_parent->recursive_quiesce_counter; i++) {
-        bdrv_do_drained_end(child->bs, true, child, false,
-                            &drained_end_counter);
+        bdrv_do_drained_end(child->bs, true, child, false);
     }
-
-    BDRV_POLL_WHILE(child->bs, qatomic_read(&drained_end_counter) > 0);
 }
 
 void bdrv_drain(BlockDriverState *bs)
@@ -610,7 +565,7 @@ void bdrv_drain_all_begin(void)
     GLOBAL_STATE_CODE();
 
     if (qemu_in_coroutine()) {
-        bdrv_co_yield_to_drain(NULL, true, false, NULL, true, true, NULL);
+        bdrv_co_yield_to_drain(NULL, true, false, NULL, true, true);
         return;
     }
 
@@ -649,22 +604,19 @@ void bdrv_drain_all_begin(void)
 
 void bdrv_drain_all_end_quiesce(BlockDriverState *bs)
 {
-    int drained_end_counter = 0;
     GLOBAL_STATE_CODE();
 
     g_assert(bs->quiesce_counter > 0);
     g_assert(!bs->refcnt);
 
     while (bs->quiesce_counter) {
-        bdrv_do_drained_end(bs, false, NULL, true, &drained_end_counter);
+        bdrv_do_drained_end(bs, false, NULL, true);
     }
-    BDRV_POLL_WHILE(bs, qatomic_read(&drained_end_counter) > 0);
 }
 
 void bdrv_drain_all_end(void)
 {
     BlockDriverState *bs = NULL;
-    int drained_end_counter = 0;
     GLOBAL_STATE_CODE();
 
     /*
@@ -680,13 +632,11 @@ void bdrv_drain_all_end(void)
         AioContext *aio_context = bdrv_get_aio_context(bs);
 
         aio_context_acquire(aio_context);
-        bdrv_do_drained_end(bs, false, NULL, true, &drained_end_counter);
+        bdrv_do_drained_end(bs, false, NULL, true);
         aio_context_release(aio_context);
     }
 
     assert(qemu_get_current_aio_context() == qemu_get_aio_context());
-    AIO_WAIT_WHILE(NULL, qatomic_read(&drained_end_counter) > 0);
-
     assert(bdrv_drain_all_count > 0);
     bdrv_drain_all_count--;
 }
diff --git a/blockjob.c b/blockjob.c
index f51d4e18f3..0ab721e139 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -120,7 +120,7 @@ static bool child_job_drained_poll(BdrvChild *c)
     }
 }
 
-static void child_job_drained_end(BdrvChild *c, int *drained_end_counter)
+static void child_job_drained_end(BdrvChild *c)
 {
     BlockJob *job = c->opaque;
     job_resume(&job->job);
diff --git a/include/block/block-io.h b/include/block/block-io.h
index b099d7db45..054e964c9b 100644
--- a/include/block/block-io.h
+++ b/include/block/block-io.h
@@ -237,21 +237,6 @@ int coroutine_fn bdrv_co_copy_range(BdrvChild *src, int64_t src_offset,
                                     int64_t bytes, BdrvRequestFlags read_flags,
                                     BdrvRequestFlags write_flags);
 
-/**
- * bdrv_drained_end_no_poll:
- *
- * Same as bdrv_drained_end(), but do not poll for the subgraph to
- * actually become unquiesced.  Therefore, no graph changes will occur
- * with this function.
- *
- * *drained_end_counter is incremented for every background operation
- * that is scheduled, and will be decremented for every operation once
- * it settles.  The caller must poll until it reaches 0.  The counter
- * should be accessed using atomic operations only.
- */
-void bdrv_drained_end_no_poll(BlockDriverState *bs, int *drained_end_counter);
-
-
 /*
  * "I/O or GS" API functions. These functions can run without
  * the BQL, but only in one specific iothread/main loop.
@@ -311,9 +296,6 @@ void bdrv_parent_drained_begin_single(BdrvChild *c, bool poll);
  * bdrv_parent_drained_end_single:
  *
  * End a quiesced section for the parent of @c.
- *
- * This polls @bs's AioContext until all scheduled sub-drained_ends
- * have settled, which may result in graph changes.
  */
 void bdrv_parent_drained_end_single(BdrvChild *c);
 
@@ -361,12 +343,6 @@ void bdrv_subtree_drained_begin(BlockDriverState *bs);
  * bdrv_drained_end:
  *
  * End a quiescent section started by bdrv_drained_begin().
- *
- * This polls @bs's AioContext until all scheduled sub-drained_ends
- * have settled.  On one hand, that may result in graph changes.  On
- * the other, this requires that the caller either runs in the main
- * loop; or that all involved nodes (@bs and all of its parents) are
- * in the caller's AioContext.
  */
 void bdrv_drained_end(BlockDriverState *bs);
 
diff --git a/include/block/block_int-common.h b/include/block/block_int-common.h
index 40d646d1ed..2b97576f6d 100644
--- a/include/block/block_int-common.h
+++ b/include/block/block_int-common.h
@@ -939,15 +939,11 @@ struct BdrvChildClass {
      * These functions must not change the graph (and therefore also must not
      * call aio_poll(), which could change the graph indirectly).
      *
-     * If drained_end() schedules background operations, it must atomically
-     * increment *drained_end_counter for each such operation and atomically
-     * decrement it once the operation has settled.
-     *
      * Note that this can be nested. If drained_begin() was called twice, new
      * I/O is allowed only after drained_end() was called twice, too.
      */
     void (*drained_begin)(BdrvChild *child);
-    void (*drained_end)(BdrvChild *child, int *drained_end_counter);
+    void (*drained_end)(BdrvChild *child);
 
     /*
      * Returns whether the parent has pending requests for the child. This
-- 
2.31.1