diff --git a/mm/shmem.c b/mm/shmem.c
index 9b90d89..793dcd1 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -89,7 +89,8 @@
 	SGP_READ,	/* don't exceed i_size, don't allocate page */
 	SGP_CACHE,	/* don't exceed i_size, may allocate page */
 	SGP_DIRTY,	/* like SGP_CACHE, but set new page dirty */
-	SGP_WRITE,	/* may exceed i_size, may allocate page */
+	SGP_WRITE,	/* may exceed i_size, may allocate !Uptodate page */
+	SGP_FALLOC,	/* like SGP_WRITE, but make existing page Uptodate */
 };
 
 #ifdef CONFIG_TMPFS
@@ -427,8 +428,10 @@
 
 /*
  * Remove range of pages and swap entries from radix tree, and free them.
+ * If !unfalloc, truncate or punch hole; if unfalloc, undo failed fallocate.
  */
-void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
+static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
+								 bool unfalloc)
 {
 	struct address_space *mapping = inode->i_mapping;
 	struct shmem_inode_info *info = SHMEM_I(inode);
@@ -462,6 +465,8 @@
 				break;
 
 			if (radix_tree_exceptional_entry(page)) {
+				if (unfalloc)
+					continue;
 				nr_swaps_freed += !shmem_free_swap(mapping,
 								index, page);
 				continue;
@@ -469,9 +474,11 @@
 
 			if (!trylock_page(page))
 				continue;
-			if (page->mapping == mapping) {
-				VM_BUG_ON(PageWriteback(page));
-				truncate_inode_page(mapping, page);
+			if (!unfalloc || !PageUptodate(page)) {
+				if (page->mapping == mapping) {
+					VM_BUG_ON(PageWriteback(page));
+					truncate_inode_page(mapping, page);
+				}
 			}
 			unlock_page(page);
 		}
@@ -517,12 +524,12 @@
 				min(end - index, (pgoff_t)PAGEVEC_SIZE),
 							pvec.pages, indices);
 		if (!pvec.nr) {
-			if (index == start)
+			if (index == start || unfalloc)
 				break;
 			index = start;
 			continue;
 		}
-		if (index == start && indices[0] >= end) {
+		if ((index == start || unfalloc) && indices[0] >= end) {
 			shmem_deswap_pagevec(&pvec);
 			pagevec_release(&pvec);
 			break;
@@ -536,15 +543,19 @@
 				break;
 
 			if (radix_tree_exceptional_entry(page)) {
+				if (unfalloc)
+					continue;
 				nr_swaps_freed += !shmem_free_swap(mapping,
 								index, page);
 				continue;
 			}
 
 			lock_page(page);
-			if (page->mapping == mapping) {
-				VM_BUG_ON(PageWriteback(page));
-				truncate_inode_page(mapping, page);
+			if (!unfalloc || !PageUptodate(page)) {
+				if (page->mapping == mapping) {
+					VM_BUG_ON(PageWriteback(page));
+					truncate_inode_page(mapping, page);
+				}
 			}
 			unlock_page(page);
 		}
@@ -558,7 +569,11 @@
 	info->swapped -= nr_swaps_freed;
 	shmem_recalc_inode(inode);
 	spin_unlock(&info->lock);
+}
 
+void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
+{
+	shmem_undo_range(inode, lstart, lend, false);
 	inode->i_ctime = inode->i_mtime = CURRENT_TIME;
 }
 EXPORT_SYMBOL_GPL(shmem_truncate_range);
@@ -771,6 +786,18 @@
 		WARN_ON_ONCE(1);	/* Still happens? Tell us about it! */
 		goto redirty;
 	}
+
+	/*
+	 * This is somewhat ridiculous, but without plumbing a SWAP_MAP_FALLOC
+	 * value into swapfile.c, the only way we can correctly account for a
+	 * fallocated page arriving here is now to initialize it and write it.
+	 */
+	if (!PageUptodate(page)) {
+		clear_highpage(page);
+		flush_dcache_page(page);
+		SetPageUptodate(page);
+	}
+
 	swap = get_swap_page();
 	if (!swap.val)
 		goto redirty;
@@ -994,6 +1021,7 @@
 	swp_entry_t swap;
 	int error;
 	int once = 0;
+	int alloced = 0;
 
 	if (index > (MAX_LFS_FILESIZE >> PAGE_CACHE_SHIFT))
 		return -EFBIG;
@@ -1005,19 +1033,21 @@
 		page = NULL;
 	}
 
-	if (sgp != SGP_WRITE &&
+	if (sgp != SGP_WRITE && sgp != SGP_FALLOC &&
 	    ((loff_t)index << PAGE_CACHE_SHIFT) >= i_size_read(inode)) {
 		error = -EINVAL;
 		goto failed;
 	}
 
+	/* fallocated page? */
+	if (page && !PageUptodate(page)) {
+		if (sgp != SGP_READ)
+			goto clear;
+		unlock_page(page);
+		page_cache_release(page);
+		page = NULL;
+	}
 	if (page || (sgp == SGP_READ && !swap.val)) {
-		/*
-		 * Once we can get the page lock, it must be uptodate:
-		 * if there were an error in reading back from swap,
-		 * the page would not be inserted into the filecache.
-		 */
-		BUG_ON(page && !PageUptodate(page));
 		*pagep = page;
 		return 0;
 	}
@@ -1114,9 +1144,18 @@
 		inode->i_blocks += BLOCKS_PER_PAGE;
 		shmem_recalc_inode(inode);
 		spin_unlock(&info->lock);
+		alloced = true;
 
 		/*
-		 * Let SGP_WRITE caller clear ends if write does not fill page
+		 * Let SGP_FALLOC use the SGP_WRITE optimization on a new page.
+		 */
+		if (sgp == SGP_FALLOC)
+			sgp = SGP_WRITE;
+clear:
+		/*
+		 * Let SGP_WRITE caller clear ends if write does not fill page;
+		 * but SGP_FALLOC on a page fallocated earlier must initialize
+		 * it now, lest undo on failure cancel our earlier guarantee.
 		 */
 		if (sgp != SGP_WRITE) {
 			clear_highpage(page);
@@ -1128,10 +1167,13 @@
 	}
 
 	/* Perhaps the file has been truncated since we checked */
-	if (sgp != SGP_WRITE &&
+	if (sgp != SGP_WRITE && sgp != SGP_FALLOC &&
 	    ((loff_t)index << PAGE_CACHE_SHIFT) >= i_size_read(inode)) {
 		error = -EINVAL;
-		goto trunc;
+		if (alloced)
+			goto trunc;
+		else
+			goto failed;
 	}
 	*pagep = page;
 	return 0;
@@ -1140,6 +1182,7 @@
 	 * Error recovery.
 	 */
 trunc:
+	info = SHMEM_I(inode);
 	ClearPageDirty(page);
 	delete_from_page_cache(page);
 	spin_lock(&info->lock);
@@ -1147,6 +1190,7 @@
 	inode->i_blocks -= BLOCKS_PER_PAGE;
 	spin_unlock(&info->lock);
 decused:
+	sbinfo = SHMEM_SB(inode->i_sb);
 	if (sbinfo->max_blocks)
 		percpu_counter_add(&sbinfo->used_blocks, -1);
 unacct:
@@ -1645,25 +1689,20 @@
 		if (signal_pending(current))
 			error = -EINTR;
 		else
-			error = shmem_getpage(inode, index, &page, SGP_WRITE,
+			error = shmem_getpage(inode, index, &page, SGP_FALLOC,
 									NULL);
 		if (error) {
-			/*
-			 * We really ought to free what we allocated so far,
-			 * but it would be wrong to free pages allocated
-			 * earlier, or already now in use: i_mutex does not
-			 * exclude all cases.  We do not know what to free.
-			 */
+			/* Remove the !PageUptodate pages we added */
+			shmem_undo_range(inode,
+				(loff_t)start << PAGE_CACHE_SHIFT,
+				(loff_t)index << PAGE_CACHE_SHIFT, true);
 			goto ctime;
 		}
 
-		if (!PageUptodate(page)) {
-			clear_highpage(page);
-			flush_dcache_page(page);
-			SetPageUptodate(page);
-		}
 		/*
-		 * set_page_dirty so that memory pressure will swap rather
+		 * If !PageUptodate, leave it that way so that freeable pages
+		 * can be recognized if we need to rollback on error later.
+		 * But set_page_dirty so that memory pressure will swap rather
 		 * than free the pages we are allocating (and SGP_CACHE pages
 		 * might still be clean: we now need to mark those dirty too).
 		 */