Re: [bug report] iomap: write iomap validity checks

[Matthew Wilcox <willy@infradead.org>]

On Fri, Jan 20, 2023 at 04:47:04PM +0300, Dan Carpenter wrote:
> Hello Dave Chinner,
> 
> The patch d7b64041164c: "iomap: write iomap validity checks" from Nov
> 29, 2022, leads to the following Smatch static checker warning:
> 
> 	fs/iomap/buffered-io.c:829 iomap_write_iter()
> 	error: uninitialized symbol 'folio'.
> 
> fs/iomap/buffered-io.c
>     818                 if (unlikely(fault_in_iov_iter_readable(i, bytes) == bytes)) {
>     819                         status = -EFAULT;
>     820                         break;
>     821                 }
>     822 
>     823                 status = iomap_write_begin(iter, pos, bytes, &folio);
>                                                                      ^^^^^^^
> The iomap_write_begin() function can succeed without initializing
> *foliop.  It's next to the big comment.

Yes, but if it does, it sets IOMAP_F_STALE

>     824                 if (unlikely(status))
>     825                         break;
>     826                 if (iter->iomap.flags & IOMAP_F_STALE)
>     827                         break;

so it breaks out here.  Maybe we should return an errno from
iomap_write_begin() to make life easier for the static checking tools?

> --> 829                 page = folio_file_page(folio, pos >> PAGE_SHIFT);
>                                                ^^^^^
> 
>     830                 if (mapping_writably_mapped(mapping))
>     831                         flush_dcache_page(page);