Re: [PATCH 03/24] block: Mark bdrv_filter_bs() and callers GRAPH_RDLOCK

[Eric Blake]

On Fri, Oct 27, 2023 at 03:02:38PM -0500, Eric Blake wrote:
> On Fri, Oct 27, 2023 at 05:53:12PM +0200, Kevin Wolf wrote:
> > This adds GRAPH_RDLOCK annotations to declare that callers of
> > bdrv_filter_bs() need to hold a reader lock for the graph because
> > it calls bdrv_filter_child(), which accesses bs->file/backing.
> > 
> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> > ---
> >  include/block/block-io.h       | 2 +-
> >  include/block/block_int-io.h   | 3 ++-
> >  block.c                        | 9 +++++++--
> >  block/stream.c                 | 2 ++
> >  migration/block-dirty-bitmap.c | 4 ++++
> >  5 files changed, 16 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/block/block-io.h b/include/block/block-io.h
> > index ad270b6ad2..58c4cf50a0 100644
> > --- a/include/block/block-io.h
> > +++ b/include/block/block-io.h
> > @@ -183,7 +183,7 @@ bdrv_co_eject(BlockDriverState *bs, bool eject_flag);
> >  
> >  const char *bdrv_get_format_name(BlockDriverState *bs);
> >  
> > -bool bdrv_supports_compressed_writes(BlockDriverState *bs);
> > +bool GRAPH_RDLOCK bdrv_supports_compressed_writes(BlockDriverState *bs);
> 
> Unrelated change that belongs elsewhere in the series?

Answering myself:

bdrv_supports_compressed_writes() calls bdrv_filter_bs(), and is
itself called only by backup_job_create() which already uses
GRAPH_RDLOCK_GUARD_MAINLOOP().  It wasn't obvious in the diff, but
looking at the bigger context it makes sense.  Maybe calling it out in
the commit message would help future readers, though.

> 
> Otherwise,
> Reviewed-by: Eric Blake <eblake@redhat.com>

R-b stands.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization:  qemu.org | libguestfs.org