Re: [Qemu-devel] Block Migration Assertion in qemu-kvm 1.2.0

[Kevin Wolf <kwolf@redhat.com>]

Am 18.09.2012 12:28, schrieb Peter Lieven:
> On 09/17/12 22:12, Peter Lieven wrote:
>> On 09/17/12 10:41, Kevin Wolf wrote:
>>> Am 16.09.2012 12:13, schrieb Peter Lieven:
>>>> Hi,
>>>>
>>>> when trying to block migrate a VM from one node to another, the source
>>>> VM crashed with the following assertion:
>>>> block.c:3829: bdrv_set_in_use: Assertion `bs->in_use != in_use' failed.
>>>>
>>>> Is this sth already addresses/known?
>>> Not that I'm aware of, at least.
>>>
>>> Block migration doesn't seem to check whether the device is already in
>>> use, maybe this is the problem. Not sure why it would be in use, though,
>>> and in my quick test it didn't crash.
>>>
>>> So we need some more information: What's you command line, did you do
>>> anything specific in the monitor with block devices, what does the
>>> stacktrace look like, etc.?
>> kevin, it seems that i can very easily force a crash if I cancel a 
>> running block migration.
> if I understand correctly what happens there are aio callbacks coming in 
> after
> blk_mig_cleanup() has been called.
> 
> what is the proper way to detect this in blk_mig_read_cb()?

You could try this, it doesn't detect the situation in
blk_mig_read_cb(), but ensures that all callbacks happen before we do
the actual cleanup (completely untested):

diff --git a/block-migration.c b/block-migration.c
index 7def8ab..ed93301 100644
--- a/block-migration.c
+++ b/block-migration.c
@@ -519,6 +519,8 @@ static void blk_mig_cleanup(void)
     BlkMigDevState *bmds;
     BlkMigBlock *blk;

+    bdrv_drain_all();
+
     set_dirty_tracking(0);

     while ((bmds = QSIMPLEQ_FIRST(&block_mig_state.bmds_list)) != NULL) {