Hi Kent,

I love your patch! Yet something to improve:

[auto build test ERROR on linus/master]
[also build test ERROR on v4.18 next-20180816]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Kent-Overstreet/generic_file_buffered_read-improvements/20180816-200515
config: sparc64-allmodconfig (attached as .config)
compiler: sparc64-linux-gnu-gcc (Debian 7.2.0-11) 7.2.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=7.2.0 make.cross ARCH=sparc64 

All errors (new ones prefixed by >>):

   mm/filemap.c: In function 'generic_file_buffered_read':
>> mm/filemap.c:2340:23: error: 'page' undeclared (first use in this function)
        flush_dcache_page(page);
                          ^~~~
   mm/filemap.c:2340:23: note: each undeclared identifier is reported only once for each function it appears in

vim +/page +2340 mm/filemap.c

  2253	
  2254	/**
  2255	 * generic_file_buffered_read - generic file read routine
  2256	 * @iocb:	the iocb to read
  2257	 * @iter:	data destination
  2258	 * @written:	already copied
  2259	 *
  2260	 * This is a generic file read routine, and uses the
  2261	 * mapping->a_ops->readpage() function for the actual low-level stuff.
  2262	 *
  2263	 * This is really ugly. But the goto's actually try to clarify some
  2264	 * of the logic when it comes to error handling etc.
  2265	 */
  2266	static ssize_t generic_file_buffered_read(struct kiocb *iocb,
  2267			struct iov_iter *iter, ssize_t written)
  2268	{
  2269		struct file *filp = iocb->ki_filp;
  2270		struct file_ra_state *ra = &filp->f_ra;
  2271		struct address_space *mapping = filp->f_mapping;
  2272		struct inode *inode = mapping->host;
  2273		size_t orig_count = iov_iter_count(iter);
  2274		struct page *pages[64];
  2275		int i, pg_nr, error = 0;
  2276		bool writably_mapped;
  2277		loff_t isize, end_offset;
  2278	
  2279		if (unlikely(iocb->ki_pos >= inode->i_sb->s_maxbytes))
  2280			return 0;
  2281		iov_iter_truncate(iter, inode->i_sb->s_maxbytes);
  2282	
  2283		do {
  2284			cond_resched();
  2285	
  2286			i = 0;
  2287			pg_nr = generic_file_buffered_read_get_pages(iocb, iter, pages,
  2288								     ARRAY_SIZE(pages));
  2289			if (pg_nr < 0) {
  2290				error = pg_nr;
  2291				break;
  2292			}
  2293	
  2294			/*
  2295			 * i_size must be checked after we know the pages are Uptodate.
  2296			 *
  2297			 * Checking i_size after the check allows us to calculate
  2298			 * the correct value for "nr", which means the zero-filled
  2299			 * part of the page is not copied back to userspace (unless
  2300			 * another truncate extends the file - this is desired though).
  2301			 */
  2302			isize = i_size_read(inode);
  2303			if (unlikely(iocb->ki_pos >= isize))
  2304				goto put_pages;
  2305	
  2306			end_offset = min_t(loff_t, isize, iocb->ki_pos + iter->count);
  2307	
  2308			while ((iocb->ki_pos >> PAGE_SHIFT) + pg_nr >
  2309			       (end_offset + PAGE_SIZE - 1) >> PAGE_SHIFT)
  2310				put_page(pages[--pg_nr]);
  2311	
  2312			/*
  2313			 * Once we start copying data, we don't want to be touching any
  2314			 * cachelines that might be contended:
  2315			 */
  2316			writably_mapped = mapping_writably_mapped(mapping);
  2317	
  2318			/*
  2319			 * When a sequential read accesses a page several times, only
  2320			 * mark it as accessed the first time.
  2321			 */
  2322			if (iocb->ki_pos >> PAGE_SHIFT !=
  2323			    ra->prev_pos >> PAGE_SHIFT)
  2324				mark_page_accessed(pages[0]);
  2325			for (i = 1; i < pg_nr; i++)
  2326				mark_page_accessed(pages[i]);
  2327	
  2328			for (i = 0; i < pg_nr; i++) {
  2329				unsigned offset = iocb->ki_pos & ~PAGE_MASK;
  2330				unsigned bytes = min_t(loff_t, end_offset - iocb->ki_pos,
  2331						       PAGE_SIZE - offset);
  2332				unsigned copied;
  2333	
  2334				/*
  2335				 * If users can be writing to this page using arbitrary
  2336				 * virtual addresses, take care about potential aliasing
  2337				 * before reading the page on the kernel side.
  2338				 */
  2339				if (writably_mapped)
> 2340					flush_dcache_page(page);
  2341	
  2342				copied = copy_page_to_iter(pages[i], offset, bytes, iter);
  2343	
  2344				iocb->ki_pos += copied;
  2345				ra->prev_pos = iocb->ki_pos;
  2346	
  2347				if (copied < bytes) {
  2348					error = -EFAULT;
  2349					break;
  2350				}
  2351			}
  2352	put_pages:
  2353			for (i = 0; i < pg_nr; i++)
  2354				put_page(pages[i]);
  2355		} while (iov_iter_count(iter) && iocb->ki_pos < isize && !error);
  2356	
  2357		file_accessed(filp);
  2358		written += orig_count - iov_iter_count(iter);
  2359	
  2360		return written ? written : error;
  2361	}
  2362	

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