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