Merge tag 'for-upstream' of https://repo.or.cz/qemu/kevin into staging

Block layer patches

- Graph locking part 4 (node management)
- qemu-img map: report compressed data blocks
- block-backend: process I/O in the current AioContext

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# gpg: Signature made Wed 20 Sep 2023 12:31:49 EDT
# gpg:                using RSA key DC3DEB159A9AF95D3D7456FE7F09B272C88F2FD6
# gpg:                issuer "kwolf@redhat.com"
# gpg: Good signature from "Kevin Wolf <kwolf@redhat.com>" [full]
# Primary key fingerprint: DC3D EB15 9A9A F95D 3D74  56FE 7F09 B272 C88F 2FD6

* tag 'for-upstream' of https://repo.or.cz/qemu/kevin: (28 commits)
  block: mark aio_poll as non-coroutine
  block-backend: process zoned requests in the current AioContext
  block-backend: process I/O in the current AioContext
  test-bdrv-drain: avoid race with BH in IOThread drain test
  block: remove AIOCBInfo->get_aio_context()
  qemu-img: map: report compressed data blocks
  block: add BDRV_BLOCK_COMPRESSED flag for bdrv_block_status()
  block: Mark bdrv_add/del_child() and caller GRAPH_WRLOCK
  block: Mark bdrv_unref_child() GRAPH_WRLOCK
  block: Mark bdrv_root_unref_child() GRAPH_WRLOCK
  block: Take graph rdlock in bdrv_change_aio_context()
  block: Take graph rdlock in bdrv_drop_intermediate()
  block: Mark bdrv_parent_cb_change_media() GRAPH_RDLOCK
  block: Mark bdrv_child_perm() GRAPH_RDLOCK
  block: Mark bdrv_get_cumulative_perm() and callers GRAPH_RDLOCK
  block: Mark bdrv_parent_perms_conflict() and callers GRAPH_RDLOCK
  block: Mark bdrv_attach_child() GRAPH_WRLOCK
  block: Call transaction callbacks with lock held
  block: Mark bdrv_attach_child_common() GRAPH_WRLOCK
  block: Mark bdrv_replace_child_tran() GRAPH_WRLOCK
  ...

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

16 files changed, 232 insertions, 125 deletions

diff --git a/block/blklogwrites.c b/block/blklogwrites.c
index 3ea7141cb5..a0d70729bb 100644
--- a/block/blklogwrites.c
+++ b/block/blklogwrites.c
@@ -251,7 +251,9 @@ static int blk_log_writes_open(BlockDriverState *bs, QDict *options, int flags,
     ret = 0;
 fail_log:
     if (ret < 0) {
+        bdrv_graph_wrlock(NULL);
         bdrv_unref_child(bs, s->log_file);
+        bdrv_graph_wrunlock();
         s->log_file = NULL;
     }
 fail:
@@ -263,8 +265,10 @@ static void blk_log_writes_close(BlockDriverState *bs)
 {
     BDRVBlkLogWritesState *s = bs->opaque;
 
+    bdrv_graph_wrlock(NULL);
     bdrv_unref_child(bs, s->log_file);
     s->log_file = NULL;
+    bdrv_graph_wrunlock();
 }
 
 static int64_t coroutine_fn GRAPH_RDLOCK
diff --git a/block/blkverify.c b/block/blkverify.c
index 7326461f30..dae9716a26 100644
--- a/block/blkverify.c
+++ b/block/blkverify.c
@@ -151,8 +151,10 @@ static void blkverify_close(BlockDriverState *bs)
 {
     BDRVBlkverifyState *s = bs->opaque;
 
+    bdrv_graph_wrlock(NULL);
     bdrv_unref_child(bs, s->test_file);
     s->test_file = NULL;
+    bdrv_graph_wrunlock();
 }
 
 static int64_t coroutine_fn GRAPH_RDLOCK
diff --git a/block/block-backend.c b/block/block-backend.c
index 47d360c97a..efe2e7cbf8 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -33,8 +33,6 @@
 
 #define NOT_DONE 0x7fffffff /* used while emulated sync operation in progress */
 
-static AioContext *blk_aiocb_get_aio_context(BlockAIOCB *acb);
-
 typedef struct BlockBackendAioNotifier {
     void (*attached_aio_context)(AioContext *new_context, void *opaque);
     void (*detach_aio_context)(void *opaque);
@@ -103,7 +101,6 @@ typedef struct BlockBackendAIOCB {
 } BlockBackendAIOCB;
 
 static const AIOCBInfo block_backend_aiocb_info = {
-    .get_aio_context = blk_aiocb_get_aio_context,
     .aiocb_size = sizeof(BlockBackendAIOCB),
 };
 
@@ -121,6 +118,10 @@ static QTAILQ_HEAD(, BlockBackend) block_backends =
 static QTAILQ_HEAD(, BlockBackend) monitor_block_backends =
     QTAILQ_HEAD_INITIALIZER(monitor_block_backends);
 
+static int coroutine_mixed_fn GRAPH_RDLOCK
+blk_set_perm_locked(BlockBackend *blk, uint64_t perm, uint64_t shared_perm,
+                    Error **errp);
+
 static void blk_root_inherit_options(BdrvChildRole role, bool parent_is_format,
                                      int *child_flags, QDict *child_options,
                                      int parent_flags, QDict *parent_options)
@@ -186,7 +187,7 @@ static void blk_vm_state_changed(void *opaque, bool running, RunState state)
  *
  * If an error is returned, the VM cannot be allowed to be resumed.
  */
-static void blk_root_activate(BdrvChild *child, Error **errp)
+static void GRAPH_RDLOCK blk_root_activate(BdrvChild *child, Error **errp)
 {
     BlockBackend *blk = child->opaque;
     Error *local_err = NULL;
@@ -207,7 +208,7 @@ static void blk_root_activate(BdrvChild *child, Error **errp)
      */
     saved_shared_perm = blk->shared_perm;
 
-    blk_set_perm(blk, blk->perm, BLK_PERM_ALL, &local_err);
+    blk_set_perm_locked(blk, blk->perm, BLK_PERM_ALL, &local_err);
     if (local_err) {
         error_propagate(errp, local_err);
         blk->disable_perm = true;
@@ -226,7 +227,7 @@ static void blk_root_activate(BdrvChild *child, Error **errp)
         return;
     }
 
-    blk_set_perm(blk, blk->perm, blk->shared_perm, &local_err);
+    blk_set_perm_locked(blk, blk->perm, blk->shared_perm, &local_err);
     if (local_err) {
         error_propagate(errp, local_err);
         blk->disable_perm = true;
@@ -259,7 +260,7 @@ static bool blk_can_inactivate(BlockBackend *blk)
     return blk->force_allow_inactivate;
 }
 
-static int blk_root_inactivate(BdrvChild *child)
+static int GRAPH_RDLOCK blk_root_inactivate(BdrvChild *child)
 {
     BlockBackend *blk = child->opaque;
 
@@ -911,7 +912,10 @@ void blk_remove_bs(BlockBackend *blk)
     blk_drain(blk);
     root = blk->root;
     blk->root = NULL;
+
+    bdrv_graph_wrlock(NULL);
     bdrv_root_unref_child(root);
+    bdrv_graph_wrunlock();
 }
 
 /*
@@ -953,8 +957,9 @@ int blk_replace_bs(BlockBackend *blk, BlockDriverState *new_bs, Error **errp)
 /*
  * Sets the permission bitmasks that the user of the BlockBackend needs.
  */
-int blk_set_perm(BlockBackend *blk, uint64_t perm, uint64_t shared_perm,
-                 Error **errp)
+static int coroutine_mixed_fn GRAPH_RDLOCK
+blk_set_perm_locked(BlockBackend *blk, uint64_t perm, uint64_t shared_perm,
+                    Error **errp)
 {
     int ret;
     GLOBAL_STATE_CODE();
@@ -972,6 +977,15 @@ int blk_set_perm(BlockBackend *blk, uint64_t perm, uint64_t shared_perm,
     return 0;
 }
 
+int blk_set_perm(BlockBackend *blk, uint64_t perm, uint64_t shared_perm,
+                 Error **errp)
+{
+    GLOBAL_STATE_CODE();
+    GRAPH_RDLOCK_GUARD_MAINLOOP();
+
+    return blk_set_perm_locked(blk, perm, shared_perm, errp);
+}
+
 void blk_get_perm(BlockBackend *blk, uint64_t *perm, uint64_t *shared_perm)
 {
     GLOBAL_STATE_CODE();
@@ -1533,7 +1547,7 @@ BlockAIOCB *blk_abort_aio_request(BlockBackend *blk,
     acb->blk = blk;
     acb->ret = ret;
 
-    replay_bh_schedule_oneshot_event(blk_get_aio_context(blk),
+    replay_bh_schedule_oneshot_event(qemu_get_current_aio_context(),
                                      error_callback_bh, acb);
     return &acb->common;
 }
@@ -1545,16 +1559,8 @@ typedef struct BlkAioEmAIOCB {
     bool has_returned;
 } BlkAioEmAIOCB;
 
-static AioContext *blk_aio_em_aiocb_get_aio_context(BlockAIOCB *acb_)
-{
-    BlkAioEmAIOCB *acb = container_of(acb_, BlkAioEmAIOCB, common);
-
-    return blk_get_aio_context(acb->rwco.blk);
-}
-
 static const AIOCBInfo blk_aio_em_aiocb_info = {
     .aiocb_size         = sizeof(BlkAioEmAIOCB),
-    .get_aio_context    = blk_aio_em_aiocb_get_aio_context,
 };
 
 static void blk_aio_complete(BlkAioEmAIOCB *acb)
@@ -1595,11 +1601,11 @@ static BlockAIOCB *blk_aio_prwv(BlockBackend *blk, int64_t offset,
     acb->has_returned = false;
 
     co = qemu_coroutine_create(co_entry, acb);
-    aio_co_enter(blk_get_aio_context(blk), co);
+    aio_co_enter(qemu_get_current_aio_context(), co);
 
     acb->has_returned = true;
     if (acb->rwco.ret != NOT_DONE) {
-        replay_bh_schedule_oneshot_event(blk_get_aio_context(blk),
+        replay_bh_schedule_oneshot_event(qemu_get_current_aio_context(),
                                          blk_aio_complete_bh, acb);
     }
 
@@ -1901,11 +1907,11 @@ BlockAIOCB *blk_aio_zone_report(BlockBackend *blk, int64_t offset,
     acb->has_returned = false;
 
     co = qemu_coroutine_create(blk_aio_zone_report_entry, acb);
-    aio_co_enter(blk_get_aio_context(blk), co);
+    aio_co_enter(qemu_get_current_aio_context(), co);
 
     acb->has_returned = true;
     if (acb->rwco.ret != NOT_DONE) {
-        replay_bh_schedule_oneshot_event(blk_get_aio_context(blk),
+        replay_bh_schedule_oneshot_event(qemu_get_current_aio_context(),
                                          blk_aio_complete_bh, acb);
     }
 
@@ -1942,11 +1948,11 @@ BlockAIOCB *blk_aio_zone_mgmt(BlockBackend *blk, BlockZoneOp op,
     acb->has_returned = false;
 
     co = qemu_coroutine_create(blk_aio_zone_mgmt_entry, acb);
-    aio_co_enter(blk_get_aio_context(blk), co);
+    aio_co_enter(qemu_get_current_aio_context(), co);
 
     acb->has_returned = true;
     if (acb->rwco.ret != NOT_DONE) {
-        replay_bh_schedule_oneshot_event(blk_get_aio_context(blk),
+        replay_bh_schedule_oneshot_event(qemu_get_current_aio_context(),
                                          blk_aio_complete_bh, acb);
     }
 
@@ -1982,10 +1988,10 @@ BlockAIOCB *blk_aio_zone_append(BlockBackend *blk, int64_t *offset,
     acb->has_returned = false;
 
     co = qemu_coroutine_create(blk_aio_zone_append_entry, acb);
-    aio_co_enter(blk_get_aio_context(blk), co);
+    aio_co_enter(qemu_get_current_aio_context(), co);
     acb->has_returned = true;
     if (acb->rwco.ret != NOT_DONE) {
-        replay_bh_schedule_oneshot_event(blk_get_aio_context(blk),
+        replay_bh_schedule_oneshot_event(qemu_get_current_aio_context(),
                                          blk_aio_complete_bh, acb);
     }
 
@@ -2434,12 +2440,6 @@ AioContext *blk_get_aio_context(BlockBackend *blk)
     return blk->ctx;
 }
 
-static AioContext *blk_aiocb_get_aio_context(BlockAIOCB *acb)
-{
-    BlockBackendAIOCB *blk_acb = DO_UPCAST(BlockBackendAIOCB, common, acb);
-    return blk_get_aio_context(blk_acb->blk);
-}
-
 int blk_set_aio_context(BlockBackend *blk, AioContext *new_context,
                         Error **errp)
 {
diff --git a/block/copy-before-write.c b/block/copy-before-write.c
index 9a0e2b69d9..aeaff3bb82 100644
--- a/block/copy-before-write.c
+++ b/block/copy-before-write.c
@@ -341,11 +341,11 @@ static void cbw_refresh_filename(BlockDriverState *bs)
             bs->file->bs->filename);
 }
 
-static void cbw_child_perm(BlockDriverState *bs, BdrvChild *c,
-                           BdrvChildRole role,
-                           BlockReopenQueue *reopen_queue,
-                           uint64_t perm, uint64_t shared,
-                           uint64_t *nperm, uint64_t *nshared)
+static void GRAPH_RDLOCK
+cbw_child_perm(BlockDriverState *bs, BdrvChild *c, BdrvChildRole role,
+               BlockReopenQueue *reopen_queue,
+               uint64_t perm, uint64_t shared,
+               uint64_t *nperm, uint64_t *nshared)
 {
     if (!(role & BDRV_CHILD_FILTERED)) {
         /*
diff --git a/block/crypto.c b/block/crypto.c
index 6ee8d46d30..c9c9a39fa3 100644
--- a/block/crypto.c
+++ b/block/crypto.c
@@ -777,7 +777,7 @@ block_crypto_get_specific_info_luks(BlockDriverState *bs, Error **errp)
     return spec_info;
 }
 
-static int
+static int GRAPH_RDLOCK
 block_crypto_amend_prepare(BlockDriverState *bs, Error **errp)
 {
     BlockCrypto *crypto = bs->opaque;
@@ -793,7 +793,7 @@ block_crypto_amend_prepare(BlockDriverState *bs, Error **errp)
     return ret;
 }
 
-static void
+static void GRAPH_RDLOCK
 block_crypto_amend_cleanup(BlockDriverState *bs)
 {
     BlockCrypto *crypto = bs->opaque;
@@ -841,6 +841,8 @@ block_crypto_amend_options_luks(BlockDriverState *bs,
     QCryptoBlockAmendOptions *amend_options = NULL;
     int ret = -EINVAL;
 
+    assume_graph_lock(); /* FIXME */
+
     assert(crypto);
     assert(crypto->block);
 
diff --git a/block/graph-lock.c b/block/graph-lock.c
index f357a2c0b1..58a799065f 100644
--- a/block/graph-lock.c
+++ b/block/graph-lock.c
@@ -163,17 +163,29 @@ void bdrv_graph_wrlock(BlockDriverState *bs)
 void bdrv_graph_wrunlock(void)
 {
     GLOBAL_STATE_CODE();
-    QEMU_LOCK_GUARD(&aio_context_list_lock);
     assert(qatomic_read(&has_writer));
 
+    WITH_QEMU_LOCK_GUARD(&aio_context_list_lock) {
+        /*
+         * No need for memory barriers, this works in pair with
+         * the slow path of rdlock() and both take the lock.
+         */
+        qatomic_store_release(&has_writer, 0);
+
+        /* Wake up all coroutines that are waiting to read the graph */
+        qemu_co_enter_all(&reader_queue, &aio_context_list_lock);
+    }
+
     /*
-     * No need for memory barriers, this works in pair with
-     * the slow path of rdlock() and both take the lock.
+     * Run any BHs that were scheduled during the wrlock section and that
+     * callers might expect to have finished (in particular, this is important
+     * for bdrv_schedule_unref()).
+     *
+     * Do this only after restarting coroutines so that nested event loops in
+     * BHs don't deadlock if their condition relies on the coroutine making
+     * progress.
      */
-    qatomic_store_release(&has_writer, 0);
-
-    /* Wake up all coroutine that are waiting to read the graph */
-    qemu_co_enter_all(&reader_queue, &aio_context_list_lock);
+    aio_bh_poll(qemu_get_aio_context());
 }
 
 void coroutine_fn bdrv_graph_co_rdlock(void)
diff --git a/block/io.c b/block/io.c
index ba23a9bcd3..209a6da0c8 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2950,25 +2950,18 @@ int bdrv_load_vmstate(BlockDriverState *bs, uint8_t *buf,
 /**************************************************************/
 /* async I/Os */
 
+/**
+ * Synchronously cancels an acb. Must be called with the BQL held and the acb
+ * must be processed with the BQL held too (IOThreads are not allowed).
+ *
+ * Use bdrv_aio_cancel_async() instead when possible.
+ */
 void bdrv_aio_cancel(BlockAIOCB *acb)
 {
-    IO_CODE();
+    GLOBAL_STATE_CODE();
     qemu_aio_ref(acb);
     bdrv_aio_cancel_async(acb);
-    while (acb->refcnt > 1) {
-        if (acb->aiocb_info->get_aio_context) {
-            aio_poll(acb->aiocb_info->get_aio_context(acb), true);
-        } else if (acb->bs) {
-            /* qemu_aio_ref and qemu_aio_unref are not thread-safe, so
-             * assert that we're not using an I/O thread.  Thread-safe
-             * code should use bdrv_aio_cancel_async exclusively.
-             */
-            assert(bdrv_get_aio_context(acb->bs) == qemu_get_aio_context());
-            aio_poll(bdrv_get_aio_context(acb->bs), true);
-        } else {
-            abort();
-        }
-    }
+    AIO_WAIT_WHILE_UNLOCKED(NULL, acb->refcnt > 1);
     qemu_aio_unref(acb);
 }
 
diff --git a/block/mirror.c b/block/mirror.c
index aae4bebbb6..3cc0757a03 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -702,8 +702,12 @@ static int mirror_exit_common(Job *job)
      * mirror_top_bs from now on, so keep it drained. */
     bdrv_drained_begin(mirror_top_bs);
     bs_opaque->stop = true;
+
+    bdrv_graph_rdlock_main_loop();
     bdrv_child_refresh_perms(mirror_top_bs, mirror_top_bs->backing,
                              &error_abort);
+    bdrv_graph_rdunlock_main_loop();
+
     if (!abort && s->backing_mode == MIRROR_SOURCE_BACKING_CHAIN) {
         BlockDriverState *backing = s->is_none_mode ? src : s->base;
         BlockDriverState *unfiltered_target = bdrv_skip_filters(target_bs);
@@ -1670,6 +1674,8 @@ static BlockJob *mirror_start_job(
     uint64_t target_perms, target_shared_perms;
     int ret;
 
+    GLOBAL_STATE_CODE();
+
     if (granularity == 0) {
         granularity = bdrv_get_default_bitmap_granularity(target);
     }
@@ -1906,8 +1912,10 @@ fail:
     }
 
     bs_opaque->stop = true;
+    bdrv_graph_rdlock_main_loop();
     bdrv_child_refresh_perms(mirror_top_bs, mirror_top_bs->backing,
                              &error_abort);
+    bdrv_graph_rdunlock_main_loop();
     bdrv_replace_node(mirror_top_bs, mirror_top_bs->backing->bs, &error_abort);
 
     bdrv_unref(mirror_top_bs);
diff --git a/block/preallocate.c b/block/preallocate.c
index 3d0f621003..bfb638d8b1 100644
--- a/block/preallocate.c
+++ b/block/preallocate.c
@@ -75,8 +75,14 @@ typedef struct BDRVPreallocateState {
      * be invalid (< 0) when we don't have both exclusive BLK_PERM_RESIZE and
      * BLK_PERM_WRITE permissions on file child.
      */
+
+    /* Gives up the resize permission on children when parents don't need it */
+    QEMUBH *drop_resize_bh;
 } BDRVPreallocateState;
 
+static int preallocate_drop_resize(BlockDriverState *bs, Error **errp);
+static void preallocate_drop_resize_bh(void *opaque);
+
 #define PREALLOCATE_OPT_PREALLOC_ALIGN "prealloc-align"
 #define PREALLOCATE_OPT_PREALLOC_SIZE "prealloc-size"
 static QemuOptsList runtime_opts = {
@@ -142,6 +148,7 @@ static int preallocate_open(BlockDriverState *bs, QDict *options, int flags,
      * For this to work, mark them invalid.
      */
     s->file_end = s->zero_start = s->data_end = -EINVAL;
+    s->drop_resize_bh = qemu_bh_new(preallocate_drop_resize_bh, bs);
 
     ret = bdrv_open_file_child(NULL, options, "file", bs, errp);
     if (ret < 0) {
@@ -162,26 +169,42 @@ static int preallocate_open(BlockDriverState *bs, QDict *options, int flags,
     return 0;
 }
 
-static void preallocate_close(BlockDriverState *bs)
+static int preallocate_truncate_to_real_size(BlockDriverState *bs, Error **errp)
 {
-    int ret;
     BDRVPreallocateState *s = bs->opaque;
-
-    if (s->data_end < 0) {
-        return;
-    }
+    int ret;
 
     if (s->file_end < 0) {
         s->file_end = bdrv_getlength(bs->file->bs);
         if (s->file_end < 0) {
-            return;
+            error_setg_errno(errp, -s->file_end, "Failed to get file length");
+            return s->file_end;
         }
     }
 
     if (s->data_end < s->file_end) {
         ret = bdrv_truncate(bs->file, s->data_end, true, PREALLOC_MODE_OFF, 0,
                             NULL);
-        s->file_end = ret < 0 ? ret : s->data_end;
+        if (ret < 0) {
+            error_setg_errno(errp, -ret, "Failed to drop preallocation");
+            s->file_end = ret;
+            return ret;
+        }
+        s->file_end = s->data_end;
+    }
+
+    return 0;
+}
+
+static void preallocate_close(BlockDriverState *bs)
+{
+    BDRVPreallocateState *s = bs->opaque;
+
+    qemu_bh_cancel(s->drop_resize_bh);
+    qemu_bh_delete(s->drop_resize_bh);
+
+    if (s->data_end >= 0) {
+        preallocate_truncate_to_real_size(bs, NULL);
     }
 }
 
@@ -198,6 +221,7 @@ static int preallocate_reopen_prepare(BDRVReopenState *reopen_state,
                                       BlockReopenQueue *queue, Error **errp)
 {
     PreallocateOpts *opts = g_new0(PreallocateOpts, 1);
+    int ret;
 
     if (!preallocate_absorb_opts(opts, reopen_state->options,
                                  reopen_state->bs->file->bs, errp)) {
@@ -205,6 +229,19 @@ static int preallocate_reopen_prepare(BDRVReopenState *reopen_state,
         return -EINVAL;
     }
 
+    /*
+     * Drop the preallocation already here if reopening read-only. The child
+     * might also be reopened read-only and then scheduling a BH during the
+     * permission update is too late.
+     */
+    if ((reopen_state->flags & BDRV_O_RDWR) == 0) {
+        ret = preallocate_drop_resize(reopen_state->bs, errp);
+        if (ret < 0) {
+            g_free(opts);
+            return ret;
+        }
+    }
+
     reopen_state->opaque = opts;
 
     return 0;
@@ -462,58 +499,61 @@ preallocate_co_getlength(BlockDriverState *bs)
     return ret;
 }
 
-static int preallocate_check_perm(BlockDriverState *bs,
-                                  uint64_t perm, uint64_t shared, Error **errp)
+static int preallocate_drop_resize(BlockDriverState *bs, Error **errp)
 {
     BDRVPreallocateState *s = bs->opaque;
+    int ret;
 
-    if (s->data_end >= 0 && !can_write_resize(perm)) {
-        /*
-         * Lose permissions.
-         * We should truncate in check_perm, as in set_perm bs->file->perm will
-         * be already changed, and we should not violate it.
-         */
-        if (s->file_end < 0) {
-            s->file_end = bdrv_getlength(bs->file->bs);
-            if (s->file_end < 0) {
-                error_setg(errp, "Failed to get file length");
-                return s->file_end;
-            }
-        }
+    if (s->data_end < 0) {
+        return 0;
+    }
 
-        if (s->data_end < s->file_end) {
-            int ret = bdrv_truncate(bs->file, s->data_end, true,
-                                    PREALLOC_MODE_OFF, 0, NULL);
-            if (ret < 0) {
-                error_setg(errp, "Failed to drop preallocation");
-                s->file_end = ret;
-                return ret;
-            }
-            s->file_end = s->data_end;
-        }
+    /*
+     * Before switching children to be read-only, truncate them to remove
+     * the preallocation and let them have the real size.
+     */
+    ret = preallocate_truncate_to_real_size(bs, errp);
+    if (ret < 0) {
+        return ret;
     }
 
+    /*
+     * We'll drop our permissions and will allow other users to take write and
+     * resize permissions (see preallocate_child_perm). Anyone will be able to
+     * change the child, so mark all states invalid. We'll regain control if a
+     * parent requests write access again.
+     */
+    s->data_end = s->file_end = s->zero_start = -EINVAL;
+
+    bdrv_graph_rdlock_main_loop();
+    bdrv_child_refresh_perms(bs, bs->file, NULL);
+    bdrv_graph_rdunlock_main_loop();
+
     return 0;
 }
 
+static void preallocate_drop_resize_bh(void *opaque)
+{
+    /*
+     * In case of errors, we'll simply keep the exclusive lock on the image
+     * indefinitely.
+     */
+    preallocate_drop_resize(opaque, NULL);
+}
+
 static void preallocate_set_perm(BlockDriverState *bs,
                                  uint64_t perm, uint64_t shared)
 {
     BDRVPreallocateState *s = bs->opaque;
 
     if (can_write_resize(perm)) {
+        qemu_bh_cancel(s->drop_resize_bh);
         if (s->data_end < 0) {
             s->data_end = s->file_end = s->zero_start =
-                bdrv_getlength(bs->file->bs);
+                bs->file->bs->total_sectors * BDRV_SECTOR_SIZE;
         }
     } else {
-        /*
-         * We drop our permissions, as well as allow shared
-         * permissions (see preallocate_child_perm), anyone will be able to
-         * change the child, so mark all states invalid. We'll regain control if
-         * get good permissions back.
-         */
-        s->data_end = s->file_end = s->zero_start = -EINVAL;
+        qemu_bh_schedule(s->drop_resize_bh);
     }
 }
 
@@ -521,10 +561,16 @@ static void preallocate_child_perm(BlockDriverState *bs, BdrvChild *c,
     BdrvChildRole role, BlockReopenQueue *reopen_queue,
     uint64_t perm, uint64_t shared, uint64_t *nperm, uint64_t *nshared)
 {
+    BDRVPreallocateState *s = bs->opaque;
+
     bdrv_default_perms(bs, c, role, reopen_queue, perm, shared, nperm, nshared);
 
-    if (can_write_resize(perm)) {
-        /* This should come by default, but let's enforce: */
+    /*
+     * We need exclusive write and resize permissions on the child not only when
+     * the parent can write to it, but also after the parent gave up write
+     * permissions until preallocate_drop_resize() has completed.
+     */
+    if (can_write_resize(perm) || s->data_end != -EINVAL) {
         *nperm |= BLK_PERM_WRITE | BLK_PERM_RESIZE;
 
         /*
@@ -554,7 +600,6 @@ static BlockDriver bdrv_preallocate_filter = {
     .bdrv_co_flush = preallocate_co_flush,
     .bdrv_co_truncate = preallocate_co_truncate,
 
-    .bdrv_check_perm = preallocate_check_perm,
     .bdrv_set_perm = preallocate_set_perm,
     .bdrv_child_perm = preallocate_child_perm,
 
diff --git a/block/qcow.c b/block/qcow.c
index 577bd70324..d56d24ab6d 100644
--- a/block/qcow.c
+++ b/block/qcow.c
@@ -549,7 +549,10 @@ qcow_co_block_status(BlockDriverState *bs, bool want_zero,
     if (!cluster_offset) {
         return 0;
     }
-    if ((cluster_offset & QCOW_OFLAG_COMPRESSED) || s->crypto) {
+    if (cluster_offset & QCOW_OFLAG_COMPRESSED) {
+        return BDRV_BLOCK_DATA | BDRV_BLOCK_COMPRESSED;
+    }
+    if (s->crypto) {
         return BDRV_BLOCK_DATA;
     }
     *map = cluster_offset | index_in_cluster;
diff --git a/block/qcow2.c b/block/qcow2.c
index b48cd9ce63..af43d59d76 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1880,7 +1880,7 @@ qcow2_do_open(BlockDriverState *bs, QDict *options, int flags,
     g_free(s->image_data_file);
     if (open_data_file && has_data_file(bs)) {
         bdrv_graph_co_rdunlock();
-        bdrv_unref_child(bs, s->data_file);
+        bdrv_co_unref_child(bs, s->data_file);
         bdrv_graph_co_rdlock();
         s->data_file = NULL;
     }
@@ -2162,6 +2162,9 @@ qcow2_co_block_status(BlockDriverState *bs, bool want_zero, int64_t offset,
     {
         status |= BDRV_BLOCK_RECURSE;
     }
+    if (type == QCOW2_SUBCLUSTER_COMPRESSED) {
+        status |= BDRV_BLOCK_COMPRESSED;
+    }
     return status;
 }
 
@@ -2790,7 +2793,9 @@ static void qcow2_do_close(BlockDriverState *bs, bool close_data_file)
     g_free(s->image_backing_format);
 
     if (close_data_file && has_data_file(bs)) {
+        bdrv_graph_wrlock(NULL);
         bdrv_unref_child(bs, s->data_file);
+        bdrv_graph_wrunlock();
         s->data_file = NULL;
     }
 
diff --git a/block/quorum.c b/block/quorum.c
index f28758cf2b..05220cab7f 100644
--- a/block/quorum.c
+++ b/block/quorum.c
@@ -1037,12 +1037,14 @@ static int quorum_open(BlockDriverState *bs, QDict *options, int flags,
 
 close_exit:
     /* cleanup on error */
+    bdrv_graph_wrlock(NULL);
     for (i = 0; i < s->num_children; i++) {
         if (!opened[i]) {
             continue;
         }
         bdrv_unref_child(bs, s->children[i]);
     }
+    bdrv_graph_wrunlock();
     g_free(s->children);
     g_free(opened);
 exit:
@@ -1055,15 +1057,17 @@ static void quorum_close(BlockDriverState *bs)
     BDRVQuorumState *s = bs->opaque;
     int i;
 
+    bdrv_graph_wrlock(NULL);
     for (i = 0; i < s->num_children; i++) {
         bdrv_unref_child(bs, s->children[i]);
     }
+    bdrv_graph_wrunlock();
 
     g_free(s->children);
 }
 
-static void quorum_add_child(BlockDriverState *bs, BlockDriverState *child_bs,
-                             Error **errp)
+static void GRAPH_WRLOCK
+quorum_add_child(BlockDriverState *bs, BlockDriverState *child_bs, Error **errp)
 {
     BDRVQuorumState *s = bs->opaque;
     BdrvChild *child;
@@ -1089,8 +1093,6 @@ static void quorum_add_child(BlockDriverState *bs, BlockDriverState *child_bs,
     }
     s->next_child_index++;
 
-    bdrv_drained_begin(bs);
-
     /* We can safely add the child now */
     bdrv_ref(child_bs);
 
@@ -1098,18 +1100,15 @@ static void quorum_add_child(BlockDriverState *bs, BlockDriverState *child_bs,
                               BDRV_CHILD_DATA, errp);
     if (child == NULL) {
         s->next_child_index--;
-        goto out;
+        return;
     }
     s->children = g_renew(BdrvChild *, s->children, s->num_children + 1);
     s->children[s->num_children++] = child;
     quorum_refresh_flags(bs);
-
-out:
-    bdrv_drained_end(bs);
 }
 
-static void quorum_del_child(BlockDriverState *bs, BdrvChild *child,
-                             Error **errp)
+static void GRAPH_WRLOCK
+quorum_del_child(BlockDriverState *bs, BdrvChild *child, Error **errp)
 {
     BDRVQuorumState *s = bs->opaque;
     char indexstr[INDEXSTR_LEN];
@@ -1139,16 +1138,14 @@ static void quorum_del_child(BlockDriverState *bs, BdrvChild *child,
         s->next_child_index--;
     }
 
-    bdrv_drained_begin(bs);
-
     /* We can safely remove this child now */
     memmove(&s->children[i], &s->children[i + 1],
             (s->num_children - i - 1) * sizeof(BdrvChild *));
     s->children = g_renew(BdrvChild *, s->children, --s->num_children);
+
     bdrv_unref_child(bs, child);
 
     quorum_refresh_flags(bs);
-    bdrv_drained_end(bs);
 }
 
 static void quorum_gather_child_options(BlockDriverState *bs, QDict *target,
diff --git a/block/replication.c b/block/replication.c
index ea4bf1aa80..dd166d2d82 100644
--- a/block/replication.c
+++ b/block/replication.c
@@ -542,12 +542,15 @@ static void replication_start(ReplicationState *rs, ReplicationMode mode,
             return;
         }
 
+        bdrv_graph_wrlock(bs);
+
         bdrv_ref(hidden_disk->bs);
         s->hidden_disk = bdrv_attach_child(bs, hidden_disk->bs, "hidden disk",
                                            &child_of_bds, BDRV_CHILD_DATA,
                                            &local_err);
         if (local_err) {
             error_propagate(errp, local_err);
+            bdrv_graph_wrunlock();
             aio_context_release(aio_context);
             return;
         }
@@ -558,10 +561,13 @@ static void replication_start(ReplicationState *rs, ReplicationMode mode,
                                               BDRV_CHILD_DATA, &local_err);
         if (local_err) {
             error_propagate(errp, local_err);
+            bdrv_graph_wrunlock();
             aio_context_release(aio_context);
             return;
         }
 
+        bdrv_graph_wrunlock();
+
         /* start backup job now */
         error_setg(&s->blocker,
                    "Block device is in use by internal backup job");
@@ -666,10 +672,13 @@ static void replication_done(void *opaque, int ret)
     if (ret == 0) {
         s->stage = BLOCK_REPLICATION_DONE;
 
+        bdrv_graph_wrlock(NULL);
         bdrv_unref_child(bs, s->secondary_disk);
         s->secondary_disk = NULL;
         bdrv_unref_child(bs, s->hidden_disk);
         s->hidden_disk = NULL;
+        bdrv_graph_wrunlock();
+
         s->error = 0;
     } else {
         s->stage = BLOCK_REPLICATION_FAILOVER_FAILED;
diff --git a/block/snapshot.c b/block/snapshot.c
index e22ac3eac6..b86b5b24ad 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -281,7 +281,9 @@ int bdrv_snapshot_goto(BlockDriverState *bs,
         }
 
         /* .bdrv_open() will re-attach it */
+        bdrv_graph_wrlock(NULL);
         bdrv_unref_child(bs, fallback);
+        bdrv_graph_wrunlock();
 
         ret = bdrv_snapshot_goto(fallback_bs, snapshot_id, errp);
         open_ret = drv->bdrv_open(bs, options, bs->open_flags, &local_err);
diff --git a/block/stream.c b/block/stream.c
index e522bbdec5..e4da214f1f 100644
--- a/block/stream.c
+++ b/block/stream.c
@@ -54,6 +54,7 @@ static int stream_prepare(Job *job)
 {
     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
     BlockDriverState *unfiltered_bs = bdrv_skip_filters(s->target_bs);
+    BlockDriverState *unfiltered_bs_cow = bdrv_cow_bs(unfiltered_bs);
     BlockDriverState *base;
     BlockDriverState *unfiltered_base;
     Error *local_err = NULL;
@@ -64,13 +65,18 @@ static int stream_prepare(Job *job)
     s->cor_filter_bs = NULL;
 
     /*
-     * bdrv_set_backing_hd() requires that unfiltered_bs is drained. Drain
-     * already here and use bdrv_set_backing_hd_drained() instead because
-     * the polling during drained_begin() might change the graph, and if we do
-     * this only later, we may end up working with the wrong base node (or it
-     * might even have gone away by the time we want to use it).
+     * bdrv_set_backing_hd() requires that the unfiltered_bs and the COW child
+     * of unfiltered_bs is drained. Drain already here and use
+     * bdrv_set_backing_hd_drained() instead because the polling during
+     * drained_begin() might change the graph, and if we do this only later, we
+     * may end up working with the wrong base node (or it might even have gone
+     * away by the time we want to use it).
      */
     bdrv_drained_begin(unfiltered_bs);
+    if (unfiltered_bs_cow) {
+        bdrv_ref(unfiltered_bs_cow);
+        bdrv_drained_begin(unfiltered_bs_cow);
+    }
 
     base = bdrv_filter_or_cow_bs(s->above_base);
     unfiltered_base = bdrv_skip_filters(base);
@@ -100,6 +106,10 @@ static int stream_prepare(Job *job)
     }
 
 out:
+    if (unfiltered_bs_cow) {
+        bdrv_drained_end(unfiltered_bs_cow);
+        bdrv_unref(unfiltered_bs_cow);
+    }
     bdrv_drained_end(unfiltered_bs);
     return ret;
 }
diff --git a/block/vmdk.c b/block/vmdk.c
index 58ce290e9c..e90649c8bf 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -272,6 +272,7 @@ static void vmdk_free_extents(BlockDriverState *bs)
     BDRVVmdkState *s = bs->opaque;
     VmdkExtent *e;
 
+    bdrv_graph_wrlock(NULL);
     for (i = 0; i < s->num_extents; i++) {
         e = &s->extents[i];
         g_free(e->l1_table);
@@ -282,6 +283,8 @@ static void vmdk_free_extents(BlockDriverState *bs)
             bdrv_unref_child(bs, e->file);
         }
     }
+    bdrv_graph_wrunlock();
+
     g_free(s->extents);
 }
 
@@ -1220,7 +1223,9 @@ static int vmdk_parse_extents(const char *desc, BlockDriverState *bs,
             ret = vmdk_add_extent(bs, extent_file, true, sectors,
                             0, 0, 0, 0, 0, &extent, errp);
             if (ret < 0) {
+                bdrv_graph_wrlock(NULL);
                 bdrv_unref_child(bs, extent_file);
+                bdrv_graph_wrunlock();
                 goto out;
             }
             extent->flat_start_offset = flat_offset << 9;
@@ -1235,20 +1240,26 @@ static int vmdk_parse_extents(const char *desc, BlockDriverState *bs,
             }
             g_free(buf);
             if (ret) {
+                bdrv_graph_wrlock(NULL);
                 bdrv_unref_child(bs, extent_file);
+                bdrv_graph_wrunlock();
                 goto out;
             }
             extent = &s->extents[s->num_extents - 1];
         } else if (!strcmp(type, "SESPARSE")) {
             ret = vmdk_open_se_sparse(bs, extent_file, bs->open_flags, errp);
             if (ret) {
+                bdrv_graph_wrlock(NULL);
                 bdrv_unref_child(bs, extent_file);
+                bdrv_graph_wrunlock();
                 goto out;
             }
             extent = &s->extents[s->num_extents - 1];
         } else {
             error_setg(errp, "Unsupported extent type '%s'", type);
+            bdrv_graph_wrlock(NULL);
             bdrv_unref_child(bs, extent_file);
+            bdrv_graph_wrunlock();
             ret = -ENOTSUP;
             goto out;
         }
@@ -1309,6 +1320,8 @@ static int vmdk_open(BlockDriverState *bs, QDict *options, int flags,
     BDRVVmdkState *s = bs->opaque;
     uint32_t magic;
 
+    GRAPH_RDLOCK_GUARD_MAINLOOP();
+
     ret = bdrv_open_file_child(NULL, options, "file", bs, errp);
     if (ret < 0) {
         return ret;
@@ -1770,6 +1783,8 @@ vmdk_co_block_status(BlockDriverState *bs, bool want_zero,
             if (extent->flat) {
                 ret |= BDRV_BLOCK_RECURSE;
             }
+        } else {
+            ret |= BDRV_BLOCK_COMPRESSED;
         }
         *file = extent->file->bs;
         break;