[Qemu-devel] [PULL 03/11] block: Keep DriveInfo alive until BlockDriverState dies

[Kevin Wolf <kwolf@redhat.com>]

From: Markus Armbruster <armbru@redhat.com>

If the BDS's refcnt > 0, drive_del() destroys the DriveInfo, but not
the BDS.  This can happen in three places:

* Device model destruction during unplug: blockdev_auto_del()

* Xen IDE unplug: pci_piix3_xen_ide_unplug()

* drive_del command when no device model is attached: do_drive_del()

The other callers of drive_del are on error paths where refcnt == 1.

If the user somehow manages to plug in a device model using a BDS that
has gone through drive_del(), the legacy configuration passed in
DriveInfo doesn't reach the device model, and automatic deletion on
unplug doesn't work.  Worse, some device models such as scsi-disk
crash when DriveInfo doesn't exist.

This is theoretical; I didn't research an actual reproducer. The problem
was introduced when we replaced DriveInfo reference counting by BDS
reference counting in commit a94a3fa..fa510eb.

Fix by keeping DriveInfo alive until its BDS dies.

This affects qemu_drive_opts: now you can't reuse the same ID for new
drive options until the BDS dies.  Before, you could, but since the
code always attempts to create a BDS with the same ID next, the
enclosing operation "create a new drive" failed anyway.  Different
error path, same result.

Unfortunately, the fix involves use of blockdev.c stuff from block.c,
which is a layering violation.  Fortunately, my forthcoming
BlockBackend work will get rid of it again.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Benoît Canet <benoit.canet@nodalink.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block.c                   |  2 ++
 blockdev.c                | 13 ++++++++-----
 include/sysemu/blockdev.h |  1 +
 stubs/Makefile.objs       |  1 +
 stubs/blockdev.c          | 12 ++++++++++++
 5 files changed, 24 insertions(+), 5 deletions(-)
 create mode 100644 stubs/blockdev.c

diff --git a/block.c b/block.c
index a857913..0c4540c 100644
--- a/block.c
+++ b/block.c
@@ -29,6 +29,7 @@
 #include "qemu/module.h"
 #include "qapi/qmp/qjson.h"
 #include "sysemu/sysemu.h"
+#include "sysemu/blockdev.h"    /* FIXME layering violation */
 #include "qemu/notify.h"
 #include "block/coroutine.h"
 #include "block/qapi.h"
@@ -2110,6 +2111,7 @@ static void bdrv_delete(BlockDriverState *bs)
     /* remove from list, if necessary */
     bdrv_make_anon(bs);
 
+    drive_info_del(drive_get_by_blockdev(bs));
     g_free(bs);
 }
 
diff --git a/blockdev.c b/blockdev.c
index 5ec4635..450f95c 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -216,11 +216,17 @@ static void bdrv_format_print(void *opaque, const char *name)
 
 void drive_del(DriveInfo *dinfo)
 {
+    bdrv_unref(dinfo->bdrv);
+}
+
+void drive_info_del(DriveInfo *dinfo)
+{
+    if (!dinfo) {
+        return;
+    }
     if (dinfo->opts) {
         qemu_opts_del(dinfo->opts);
     }
-
-    bdrv_unref(dinfo->bdrv);
     g_free(dinfo->id);
     QTAILQ_REMOVE(&drives, dinfo, next);
     g_free(dinfo->serial);
@@ -525,9 +531,6 @@ static DriveInfo *blockdev_init(const char *file, QDict *bs_opts,
 
 err:
     bdrv_unref(bs);
-    QTAILQ_REMOVE(&drives, dinfo, next);
-    g_free(dinfo->id);
-    g_free(dinfo);
 early_err:
     qemu_opts_del(opts);
 err_no_opts:
diff --git a/include/sysemu/blockdev.h b/include/sysemu/blockdev.h
index 23a5d10..abec381 100644
--- a/include/sysemu/blockdev.h
+++ b/include/sysemu/blockdev.h
@@ -56,6 +56,7 @@ QemuOpts *drive_add(BlockInterfaceType type, int index, const char *file,
                     const char *optstr);
 DriveInfo *drive_new(QemuOpts *arg, BlockInterfaceType block_default_type);
 void drive_del(DriveInfo *dinfo);
+void drive_info_del(DriveInfo *dinfo);
 
 /* device-hotplug */
 
diff --git a/stubs/Makefile.objs b/stubs/Makefile.objs
index 5e347d0..c0b1f6a 100644
--- a/stubs/Makefile.objs
+++ b/stubs/Makefile.objs
@@ -1,5 +1,6 @@
 stub-obj-y += arch-query-cpu-def.o
 stub-obj-y += bdrv-commit-all.o
+stub-obj-y += blockdev.o
 stub-obj-y += chr-baum-init.o
 stub-obj-y += chr-msmouse.o
 stub-obj-y += chr-testdev.o
diff --git a/stubs/blockdev.c b/stubs/blockdev.c
new file mode 100644
index 0000000..5d0a79c
--- /dev/null
+++ b/stubs/blockdev.c
@@ -0,0 +1,12 @@
+#include <assert.h>
+#include "sysemu/blockdev.h"
+
+DriveInfo *drive_get_by_blockdev(BlockDriverState *bs)
+{
+    return NULL;
+}
+
+void drive_info_del(DriveInfo *dinfo)
+{
+    assert(!dinfo);
+}
-- 
1.8.3.1