Re: [Qemu-devel] [PATCH 1/2] block: fix assert in qcow2_get_specific_info

[Paolo Bonzini]

On 20/01/2016 08:12, Denis V. Lunev wrote:
> There is a possibility to hit assert qcow2_get_specific_info that
> s->qcow_version is undefined. This happens when VM in starting from
> suspended state, i.e. it processes incoming migration, and in the same
> time 'info block' is called.
> 
> The problem is that in the qcow2_invalidate_cache closes and the image
> and memsets BDRVQcowState in the middle.
> 
> The patch moves processing of qcow2_get_specific_info into coroutine
> context and ensures that qcow2_invalidate_cache and qcow2_get_specific_info
> can not run simultaneosly.

I'm sitting next to Kevin :) and this is not a qcow2 bug.

The problem is that qcow2_invalidate_cache is being called in coroutine
context.  The process_incoming_migration_co code starting with
bdrv_invalidate_cache_all should be moved out of the coroutine and into
the main loop.  You can use a bottom half to get out of coroutine context.

The result should be a much simpler patch, too.

Thanks, and sorry for the delay.  I saw qcow2 in the title and assumed
it was something I knew nothing about. :)

Paolo