[bug report] iomap: write iomap validity checks

[Dan Carpenter <error27@gmail.com>]

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.

    824                 if (unlikely(status))
    825                         break;
    826                 if (iter->iomap.flags & IOMAP_F_STALE)
    827                         break;
    828 
--> 829                 page = folio_file_page(folio, pos >> PAGE_SHIFT);
                                               ^^^^^

    830                 if (mapping_writably_mapped(mapping))
    831                         flush_dcache_page(page);
    832 
    833                 copied = copy_page_from_iter_atomic(page, offset, bytes, i);
    834 
    835                 status = iomap_write_end(iter, pos, bytes, copied, folio);
    836 
    837                 if (unlikely(copied != status))
    838                         iov_iter_revert(i, copied - status);
    839 

regards,
dan carpenter