diff mbox series

[3/8] qcow2: Unlock the graph in qcow2_do_open() where necessary

Message ID 20230510203601.418015-4-kwolf@redhat.com
State New
Headers show
Series block: Honour graph read lock even in the main thread | expand

Commit Message

Kevin Wolf May 10, 2023, 8:35 p.m. UTC 
qcow2_do_open() calls a few no_co_wrappers that wrap functions taking
the graph lock internally as a writer. Therefore, it can't hold the
reader lock across these calls, it causes deadlocks. Drop the lock
temporarily around the calls.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/qcow2.c | 6 ++++++
 1 file changed, 6 insertions(+)

Comments

Eric Blake May 12, 2023, 4:19 p.m. UTC | #1 
On Wed, May 10, 2023 at 10:35:56PM +0200, Kevin Wolf wrote:
> 
> qcow2_do_open() calls a few no_co_wrappers that wrap functions taking
> the graph lock internally as a writer. Therefore, it can't hold the
> reader lock across these calls, it causes deadlocks. Drop the lock
> temporarily around the calls.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block/qcow2.c | 6 ++++++
>  1 file changed, 6 insertions(+)

Reviewed-by: Eric Blake <eblake@redhat.com>
diff mbox series

Patch

diff --git a/block/qcow2.c b/block/qcow2.c
index 73f36447f9..b00b4e7575 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1619,9 +1619,11 @@  qcow2_do_open(BlockDriverState *bs, QDict *options, int flags,
 
     if (open_data_file) {
         /* Open external data file */
+        bdrv_graph_co_rdunlock();
         s->data_file = bdrv_co_open_child(NULL, options, "data-file", bs,
                                           &child_of_bds, BDRV_CHILD_DATA,
                                           true, errp);
+        bdrv_graph_co_rdlock();
         if (*errp) {
             ret = -EINVAL;
             goto fail;
@@ -1629,10 +1631,12 @@  qcow2_do_open(BlockDriverState *bs, QDict *options, int flags,
 
         if (s->incompatible_features & QCOW2_INCOMPAT_DATA_FILE) {
             if (!s->data_file && s->image_data_file) {
+                bdrv_graph_co_rdunlock();
                 s->data_file = bdrv_co_open_child(s->image_data_file, options,
                                                   "data-file", bs,
                                                   &child_of_bds,
                                                   BDRV_CHILD_DATA, false, errp);
+                bdrv_graph_co_rdlock();
                 if (!s->data_file) {
                     ret = -EINVAL;
                     goto fail;
@@ -1857,7 +1861,9 @@  qcow2_do_open(BlockDriverState *bs, QDict *options, int flags,
  fail:
     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_graph_co_rdlock();
         s->data_file = NULL;
     }
     g_free(s->unknown_header_fields);