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Date: Tue, 5 Sep 2017 16:54:41 +0800
From: Fam Zheng <famz@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] block: Cleanup BMDS in bdrv_close_all
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To: Kevin Wolf <kwolf@redhat.com>
Cc: qemu-block@nongnu.org, Juan Quintela <quintela@redhat.com>, qemu-devel@nongnu.org, qemu-stable@nongnu.org, peterx@redhat.com, Max Reitz <mreitz@redhat.com>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>

On Tue, 09/05 10:44, Kevin Wolf wrote:
> Am 30.08.2017 um 12:06 hat Fam Zheng geschrieben:
> > This fixes the assertion due to op blockers added by BMDS:
> > 
> > block.c:3248: bdrv_delete: Assertion `bdrv_op_blocker_is_empty(bs)' failed.
> > 
> > Reproducer: simply start block migration and quit QEMU before it ends.
> > 
> > Cc: qemu-stable@nongnu.org
> > Signed-off-by: Fam Zheng <famz@redhat.com>
> > ---
> >  block.c                 | 2 ++
> >  migration/block.c       | 2 +-
> >  migration/block.h       | 1 +
> >  stubs/Makefile.objs     | 1 +
> >  stubs/block-migration.c | 6 ++++++
> >  5 files changed, 11 insertions(+), 1 deletion(-)
> >  create mode 100644 stubs/block-migration.c
> > 
> > diff --git a/block.c b/block.c
> > index 3308814bba..508a57274d 100644
> > --- a/block.c
> > +++ b/block.c
> > @@ -43,6 +43,7 @@
> >  #include "qemu/cutils.h"
> >  #include "qemu/id.h"
> >  #include "qapi/util.h"
> > +#include "migration/block.h"
> >  
> >  #ifdef CONFIG_BSD
> >  #include <sys/ioctl.h>
> > @@ -3111,6 +3112,7 @@ static void bdrv_close(BlockDriverState *bs)
> >  
> >  void bdrv_close_all(void)
> >  {
> > +    block_migration_cleanup_bmds();
> >      block_job_cancel_sync_all();
> >      nbd_export_close_all();
> 
> This is before bdrv_drain_all(). Can't we still have a block migration
> request in flight, whose callback will then dereference a stale pointer?

You're right, bdrv_drain_all should be called first.

Fam