> -----Original Message----- > From: Kevin Wolf [mailto:kw...@redhat.com] > Sent: 18 February 2019 10:59 > To: Paul Durrant <paul.durr...@citrix.com> > Cc: Anthony Perard <anthony.per...@citrix.com>; 'Peter Maydell' > <peter.mayd...@linaro.org>; QEMU Developers <qemu-devel@nongnu.org> > Subject: Re: [Qemu-devel] QEMU xen coverity issues > > Am 18.02.2019 um 11:28 hat Paul Durrant geschrieben: > > > -----Original Message----- > > > From: Kevin Wolf [mailto:kw...@redhat.com] > > > Sent: 18 February 2019 10:09 > > > To: Paul Durrant <paul.durr...@citrix.com> > > > Cc: 'Peter Maydell' <peter.mayd...@linaro.org>; QEMU Developers <qemu- > > > de...@nongnu.org>; Anthony Perard <anthony.per...@citrix.com> > > > Subject: Re: [Qemu-devel] QEMU xen coverity issues > > > > > > Am 15.02.2019 um 17:20 hat Paul Durrant geschrieben: > > > > > -----Original Message----- > > > > [snip] > > > > > > > > > > > > (5) CID 1398649: resource leak in xen_block_drive_create(): > > > > > > > > > > > > In hw/block/xen-block.c xen_block_drive_create() Coverity > > > > > > complains that the call "driver_layer = qdict_new()" allocates > > > > > > memory that's leaked because we don't save the pointer anywhere > > > > > > but don't deallocate it before the end of the function either. > > > > > > Coverity is not great at understanding our refcounting objects, > > > > > > but this does look like either we're missing a qobject_unref() > > > > > > or something should be keeping hold of the dictionary. Probably > > > > > > best to ask a block layer expert. > > > > > > > > > > AFAICT nothing will consume the dictionary so it does appear that > > > we're > > > > > missing an unref here. > > > > > > > > Testing proves me wrong... This one is a false positive. > > > > > > Hm, but where is it freed? > > > > > > xen_block_blockdev_add() only feeds it to an input visitor, which > > > doesn't take ownership of the QDict (and in the first error path, it > > > hasn't even done that yet). > > > > Agreed that error path does not free things... that's definitely a > > leak... but attempting to free the QDict's on return from > > xen_block_blockdev_add() certainly causes a seg fault. My assumption > > was that, having been fed through the input visitor and then through > > the output visitor in qmp_blockdev_add() that the BlockDriverState > > eventually takes ownership... but maybe that's not true? > > qmp_blockdev_add() only ever sees the QAPI object, not the original > QDict, so it should be able to take ownership of it. If anything, the > visitor could do so, but I don't think it does (it takes an extra > reference, which it frees at the end, but it doesn't free the reference > it was originally passed). > > Maybe worth having another look at that segfault? It could point to a > related, but separate bug.
What I'd failed to realize that was, having done a qdict_put_obj() to include the file_layer QDict in the driver_layer QDict, that doing a qobject_unref() on driver_layer would also implicitly unref the file_layer. I now have a patch that just unrefs driver_layer and that seems to be fine. I'll send it shortly. Paul > > Kevin