Re: [Qemu-devel] [Qemu-block] [PATCH v2] migration: re-active images while migration been canceled after inactive them

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Tue, Jan 24, 2017 at 03:59:52PM +0800, zhanghailiang wrote:
> commit fe904ea8242cbae2d7e69c052c754b8f5f1ba1d6 fixed a case
> which migration aborted QEMU because it didn't regain the control
> of images while some errors happened.
> 
> Actually, there are another two cases can trigger the same error reports:
> " bdrv_co_do_pwritev: Assertion `!(bs->open_flags & 0x0800)' failed",
> 
> Case 1, codes path:
> migration_thread()
>     migration_completion()
>         bdrv_inactivate_all() ----------------> inactivate images
>         qemu_savevm_state_complete_precopy()
>             socket_writev_buffer() --------> error because destination fails
>                 qemu_fflush() ----------------> set error on migration stream
> -> qmp_migrate_cancel() ----------------> user cancelled migration concurrently
>     -> migrate_set_state() ------------------> set migrate CANCELLIN
>     migration_completion() -----------------> go on to fail_invalidate
> 	if (s->state == MIGRATION_STATUS_ACTIVE) -> Jump this branch
> 
> Case 2, codes path:
> migration_thread()
>     migration_completion()
>         bdrv_inactivate_all() ----------------> inactivate images
>     migreation_completion() finished
> -> qmp_migrate_cancel() ---------------> user cancelled migration concurrently
>     qemu_mutex_lock_iothread();
>     qemu_bh_schedule (s->cleanup_bh);
> 
> As we can see from above, qmp_migrate_cancel can slip in whenever
> migration_thread does not hold the global lock. If this happens after
> bdrv_inactive_all() been called, the above error reports will appear.
> 
> To prevent this, we can call bdrv_invalidate_cache_all() in qmp_migrate_cancel()
> directly if we find images become inactive.
> 
> Besides, bdrv_invalidate_cache_all() in migration_completion() doesn't have the
> protection of big lock, fix it by add the missing qemu_mutex_lock_iothread();
> 
> Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
> ---
> v2:
>  - Fix a bug introduced by commit fe904 which didn't get big lock
>    before call bdrv_invalidate_cache_all. (Suggested by Dave)
> ---
>  include/migration/migration.h |  3 +++
>  migration/migration.c         | 15 +++++++++++++++
>  2 files changed, 18 insertions(+)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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