Re: [PATCH] migration: NULL transport_data after freeing

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Peter Xu (peterx@redhat.com) wrote:
> On Thu, Feb 17, 2022 at 06:04:07PM +0100, Hanna Reitz wrote:
> > migration_incoming_state_destroy() NULLs all objects it frees after they
> > are freed, presumably so that a subsequent call to the same function
> > will not free them again, unless new objects have been created in the
> > meantime.
> > 
> > transport_data is the exception, and it shows exactly this problem: When
> > an incoming migration uses transport_cleanup() and transport_data, and a
> > subsequent incoming migration (e.g. loadvm) occurs that does not, then
> > when this second one is done, it will call transport_cleanup() on the
> > old transport_data again -- which has already been freed.  This is
> > sometimes visible in the iotest 201, though for some reason I can only
> > reproduce it with -m32.
> > 
> > To fix this, call transport_cleanup() only when transport_data is not
> > NULL (otherwise there is nothing to clean up), and set transport_data to
> > NULL when it has been cleaned up (i.e. freed).
> > 
> > (transport_cleanup() is used only by migration/socket.c, where
> > socket_start_incoming_migration_internal() sets both it and
> > transport_data to non-NULL values.)
> > 
> > Signed-off-by: Hanna Reitz <hreitz@redhat.com>
> 
> I had a similar fix here:
> 
> https://lore.kernel.org/qemu-devel/20220216062809.57179-15-peterx@redhat.com/
> 
> Though there it was because I need migration_incoming_transport_cleanup()
> for other purposes, so the fix came along.
> 
> My guess is this small fix will land earlier, if so I'll rebase. :)

Actually it didn't; so since I've pulled a chunk of Peter's series in
anyway I took the one from Peter's series.

Dave

> Thanks,
> 
> -- 
> Peter Xu
> 
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK