diff mbox

[v4,1/1] block: pass the right options for BlockDriver.bdrv_open()

Message ID 20170405091909.36357-2-bjsdjshi@linux.vnet.ibm.com (mailing list archive)
State New, archived
Headers show

Commit Message

Dong Jia Shi April 5, 2017, 9:19 a.m. UTC
raw_open() expects the caller always passing in the right actual
@options parameter. But when trying to applying snapshot on a RBD
image, bdrv_snapshot_goto() calls raw_open() (by calling the
bdrv_open callback on the BlockDriver) with a NULL @options, and
that will result in a Segmentation fault.

For the other non-raw format drivers, it also makes sense to passing
in the actual options, althought they don't trigger the problem so
far.

Let's prepare a @options by adding the "file" key-value pair to a
copy of the actual options that were given for the node (i.e.
bs->options), and pass it to the callback.

BlockDriver.bdrv_open() expects bs->file to be NULL and just
overwrites it with the result from bdrv_open_child(). That means we
should actually make sure it's NULL because otherwise the child BDS
will have a reference count that is 1 too high. So we unconditionally
invoke bdrv_unref_child() before calling BlockDriver.bdrv_open(), and
we wrap everything in bdrv_ref()/bdrv_unref() so the BDS isn't
deleted in the meantime.

Suggested-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
---
 block/snapshot.c | 26 +++++++++++++++++++++++---
 1 file changed, 23 insertions(+), 3 deletions(-)

Comments

Max Reitz April 5, 2017, 1:54 p.m. UTC | #1
On 05.04.2017 11:19, Dong Jia Shi wrote:
> raw_open() expects the caller always passing in the right actual
> @options parameter. But when trying to applying snapshot on a RBD
> image, bdrv_snapshot_goto() calls raw_open() (by calling the
> bdrv_open callback on the BlockDriver) with a NULL @options, and
> that will result in a Segmentation fault.
> 
> For the other non-raw format drivers, it also makes sense to passing
> in the actual options, althought they don't trigger the problem so
> far.
> 
> Let's prepare a @options by adding the "file" key-value pair to a
> copy of the actual options that were given for the node (i.e.
> bs->options), and pass it to the callback.
> 
> BlockDriver.bdrv_open() expects bs->file to be NULL and just
> overwrites it with the result from bdrv_open_child(). That means we
> should actually make sure it's NULL because otherwise the child BDS
> will have a reference count that is 1 too high. So we unconditionally
> invoke bdrv_unref_child() before calling BlockDriver.bdrv_open(), and
> we wrap everything in bdrv_ref()/bdrv_unref() so the BDS isn't
> deleted in the meantime.
> 
> Suggested-by: Max Reitz <mreitz@redhat.com>
> Signed-off-by: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
> ---
>  block/snapshot.c | 26 +++++++++++++++++++++++---
>  1 file changed, 23 insertions(+), 3 deletions(-)

Thank you, I've applied the patch to my block branch (for inclusion in 2.9):

https://github.com/XanClic/qemu/commits/block

Max
Dong Jia Shi April 6, 2017, 1:15 a.m. UTC | #2
* Max Reitz <mreitz@redhat.com> [2017-04-05 15:54:14 +0200]:

> On 05.04.2017 11:19, Dong Jia Shi wrote:
> > raw_open() expects the caller always passing in the right actual
> > @options parameter. But when trying to applying snapshot on a RBD
> > image, bdrv_snapshot_goto() calls raw_open() (by calling the
> > bdrv_open callback on the BlockDriver) with a NULL @options, and
> > that will result in a Segmentation fault.
> > 
> > For the other non-raw format drivers, it also makes sense to passing
> > in the actual options, althought they don't trigger the problem so
> > far.
> > 
> > Let's prepare a @options by adding the "file" key-value pair to a
> > copy of the actual options that were given for the node (i.e.
> > bs->options), and pass it to the callback.
> > 
> > BlockDriver.bdrv_open() expects bs->file to be NULL and just
> > overwrites it with the result from bdrv_open_child(). That means we
> > should actually make sure it's NULL because otherwise the child BDS
> > will have a reference count that is 1 too high. So we unconditionally
> > invoke bdrv_unref_child() before calling BlockDriver.bdrv_open(), and
> > we wrap everything in bdrv_ref()/bdrv_unref() so the BDS isn't
> > deleted in the meantime.
> > 
> > Suggested-by: Max Reitz <mreitz@redhat.com>
> > Signed-off-by: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
> > ---
> >  block/snapshot.c | 26 +++++++++++++++++++++++---
> >  1 file changed, 23 insertions(+), 3 deletions(-)
> 
> Thank you, I've applied the patch to my block branch (for inclusion in 2.9):
> 
> https://github.com/XanClic/qemu/commits/block
Thank you!

> 
> Max
>
diff mbox

Patch

diff --git a/block/snapshot.c b/block/snapshot.c
index bf5c2ca..06b1185 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -27,6 +27,7 @@ 
 #include "block/block_int.h"
 #include "qapi/error.h"
 #include "qapi/qmp/qerror.h"
+#include "qapi/qmp/qstring.h"
 
 QemuOptsList internal_snapshot_opts = {
     .name = "snapshot",
@@ -189,14 +190,33 @@  int bdrv_snapshot_goto(BlockDriverState *bs,
     }
 
     if (bs->file) {
+        BlockDriverState *file;
+        QDict *options = qdict_clone_shallow(bs->options);
+        QDict *file_options;
+
+        file = bs->file->bs;
+        /* Prevent it from getting deleted when detached from bs */
+        bdrv_ref(file);
+
+        qdict_extract_subqdict(options, &file_options, "file.");
+        QDECREF(file_options);
+        qdict_put(options, "file", qstring_from_str(bdrv_get_node_name(file)));
+
         drv->bdrv_close(bs);
-        ret = bdrv_snapshot_goto(bs->file->bs, snapshot_id);
-        open_ret = drv->bdrv_open(bs, NULL, bs->open_flags, NULL);
+        bdrv_unref_child(bs, bs->file);
+        bs->file = NULL;
+
+        ret = bdrv_snapshot_goto(file, snapshot_id);
+        open_ret = drv->bdrv_open(bs, options, bs->open_flags, NULL);
+        QDECREF(options);
         if (open_ret < 0) {
-            bdrv_unref(bs->file->bs);
+            bdrv_unref(file);
             bs->drv = NULL;
             return open_ret;
         }
+
+        assert(bs->file->bs == file);
+        bdrv_unref(file);
         return ret;
     }