[bug report] staging: erofs: tidy up decompression frontend

[Dan Carpenter]

On Tue, Aug 27, 2019 at 05:36:29PM +0800, Gao Xiang wrote:
> Hi Dan,
> 
> Thanks for your report.
> 
> On Tue, Aug 27, 2019 at 12:03:55PM +0300, Dan Carpenter wrote:
> > Hello Gao Xiang,
> > 
> > This is a semi-automatic email about new static checker warnings.
> > 
> > The patch 97e86a858bc3: "staging: erofs: tidy up decompression
> > frontend" from Jul 31, 2019, leads to the following Smatch complaint:
> > 
> >     fs/erofs/zdata.c:670 z_erofs_do_read_page()
> >     error: we previously assumed 'clt->cl' could be null (see line 596)
> > 
> > fs/erofs/zdata.c
> >    595			/* didn't get a valid collection previously (very rare) */
> >    596			if (!clt->cl)
> >                             ^^^^^^^^
> > New NULL check.
> > 
> >    597				goto restart_now;
> >    598			goto hitted;
> >    599		}
> >    600	
> >    601		/* go ahead the next map_blocks */
> >    602		debugln("%s: [out-of-range] pos %llu", __func__, offset + cur);
> >    603	
> >    604		if (z_erofs_collector_end(clt))
> >    605			fe->backmost = false;
> >    606	
> >    607		map->m_la = offset + cur;
> >    608		map->m_llen = 0;
> >    609		err = z_erofs_map_blocks_iter(inode, map, 0);
> >    610		if (unlikely(err))
> >    611			goto err_out;
> >    612	
> >    613	restart_now:
> >    614		if (unlikely(!(map->m_flags & EROFS_MAP_MAPPED)))
> >    615			goto hitted;
> >    616	
> >    617		err = z_erofs_collector_begin(clt, inode, map);
> 
> At a glance, clt->cl will be all initialized in all successful paths
> in z_erofs_collector_begin, or it all fall back into err_out...
> I have no idea what is wrong here...
> 
> Some detailed path from Smatch for NIL dereferences?
> 

Ah.  Sorry for that.  It's a false positive.  I will investigate and
fix Smatch.

regards,
dan carpenter