block: Take graph lock for most of .bdrv_open

Most implementations of .bdrv_open first open their file child (which is
an operation that internally takes the write lock and therefore we
shouldn't hold the graph lock while calling it), and afterwards many
operations that require holding the graph lock, e.g. for accessing
bs->file.

This changes block drivers that follow this pattern to take the graph
lock after opening the child node.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20231027155333.420094-24-kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 10 insertions, 6 deletions

diff --git a/block/blkdebug.c b/block/blkdebug.c
index 230efa9e8d..9da8c9eddc 100644
--- a/block/blkdebug.c
+++ b/block/blkdebug.c
@@ -508,6 +508,8 @@ static int blkdebug_open(BlockDriverState *bs, QDict *options, int flags,
         goto out;
     }
 
+    bdrv_graph_rdlock_main_loop();
+
     bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
         (BDRV_REQ_FUA & bs->file->bs->supported_write_flags);
     bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
@@ -520,7 +522,7 @@ static int blkdebug_open(BlockDriverState *bs, QDict *options, int flags,
     if (s->align && (s->align >= INT_MAX || !is_power_of_2(s->align))) {
         error_setg(errp, "Cannot meet constraints with align %" PRIu64,
                    s->align);
-        goto out;
+        goto out_rdlock;
     }
     align = MAX(s->align, bs->file->bs->bl.request_alignment);
 
@@ -530,7 +532,7 @@ static int blkdebug_open(BlockDriverState *bs, QDict *options, int flags,
          !QEMU_IS_ALIGNED(s->max_transfer, align))) {
         error_setg(errp, "Cannot meet constraints with max-transfer %" PRIu64,
                    s->max_transfer);
-        goto out;
+        goto out_rdlock;
     }
 
     s->opt_write_zero = qemu_opt_get_size(opts, "opt-write-zero", 0);
@@ -539,7 +541,7 @@ static int blkdebug_open(BlockDriverState *bs, QDict *options, int flags,
          !QEMU_IS_ALIGNED(s->opt_write_zero, align))) {
         error_setg(errp, "Cannot meet constraints with opt-write-zero %" PRIu64,
                    s->opt_write_zero);
-        goto out;
+        goto out_rdlock;
     }
 
     s->max_write_zero = qemu_opt_get_size(opts, "max-write-zero", 0);
@@ -549,7 +551,7 @@ static int blkdebug_open(BlockDriverState *bs, QDict *options, int flags,
                           MAX(s->opt_write_zero, align)))) {
         error_setg(errp, "Cannot meet constraints with max-write-zero %" PRIu64,
                    s->max_write_zero);
-        goto out;
+        goto out_rdlock;
     }
 
     s->opt_discard = qemu_opt_get_size(opts, "opt-discard", 0);
@@ -558,7 +560,7 @@ static int blkdebug_open(BlockDriverState *bs, QDict *options, int flags,
          !QEMU_IS_ALIGNED(s->opt_discard, align))) {
         error_setg(errp, "Cannot meet constraints with opt-discard %" PRIu64,
                    s->opt_discard);
-        goto out;
+        goto out_rdlock;
     }
 
     s->max_discard = qemu_opt_get_size(opts, "max-discard", 0);
@@ -568,12 +570,14 @@ static int blkdebug_open(BlockDriverState *bs, QDict *options, int flags,
                           MAX(s->opt_discard, align)))) {
         error_setg(errp, "Cannot meet constraints with max-discard %" PRIu64,
                    s->max_discard);
-        goto out;
+        goto out_rdlock;
     }
 
     bdrv_debug_event(bs, BLKDBG_NONE);
 
     ret = 0;
+out_rdlock:
+    bdrv_graph_rdunlock_main_loop();
 out:
     if (ret < 0) {
         qemu_mutex_destroy(&s->lock);