NTFS: Fix read regression.

The regression was caused by:
        commit[a32ea1e1f9] Fix read/truncate race

This causes ntfs_readpage() to be called for a zero i_size inode, which
failed when the file was compressed and non-resident.

Thanks a lot to Mike Galbraith for reporting the issue and tracking down
the commit that caused the regression.

Looking into it I found three bugs which the patch fixes.

Signed-off-by: Anton Altaparmakov <aia21@cantab.net>
Tested-by:  Mike Galbraith <efault@gmx.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ntfs/aops.c

@@ -405,6 +405,15 @@ static int ntfs_readpage(struct file *file, struct page *page)
 
 retry_readpage:
 	BUG_ON(!PageLocked(page));
+	vi = page->mapping->host;
+	i_size = i_size_read(vi);
+	/* Is the page fully outside i_size? (truncate in progress) */
+	if (unlikely(page->index >= (i_size + PAGE_CACHE_SIZE - 1) >>
+			PAGE_CACHE_SHIFT)) {
+		zero_user_page(page, 0, PAGE_CACHE_SIZE, KM_USER0);
+		ntfs_debug("Read outside i_size - truncated?");
+		goto done;
+	}
 	/*
 	 * This can potentially happen because we clear PageUptodate() during
 	 * ntfs_writepage() of MstProtected() attributes.
@@ -413,7 +422,6 @@ retry_readpage:
 		unlock_page(page);
 		return 0;
 	}
-	vi = page->mapping->host;
 	ni = NTFS_I(vi);
 	/*
 	 * Only $DATA attributes can be encrypted and only unnamed $DATA

fs/ntfs/attrib.c

@@ -179,10 +179,7 @@ int ntfs_map_runlist_nolock(ntfs_inode *ni, VCN vcn, ntfs_attr_search_ctx *ctx)
 	 * ntfs_mapping_pairs_decompress() fails.
 	 */
 	end_vcn = sle64_to_cpu(a->data.non_resident.highest_vcn) + 1;
-	if (!a->data.non_resident.lowest_vcn && end_vcn == 1)
-		end_vcn = sle64_to_cpu(a->data.non_resident.allocated_size) >>
-				ni->vol->cluster_size_bits;
-	if (unlikely(vcn >= end_vcn)) {
+	if (unlikely(vcn && vcn >= end_vcn)) {
 		err = -ENOENT;
 		goto err_out;
 	}

fs/ntfs/compress.c

@@ -561,6 +561,16 @@ int ntfs_read_compressed_block(struct page *page)
 	read_unlock_irqrestore(&ni->size_lock, flags);
 	max_page = ((i_size + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT) -
 			offset;
+	/* Is the page fully outside i_size? (truncate in progress) */
+	if (xpage >= max_page) {
+		kfree(bhs);
+		kfree(pages);
+		zero_user_page(page, 0, PAGE_CACHE_SIZE, KM_USER0);
+		ntfs_debug("Compressed read outside i_size - truncated?");
+		SetPageUptodate(page);
+		unlock_page(page);
+		return 0;
+	}
 	if (nr_pages < max_page)
 		max_page = nr_pages;
 	for (i = 0; i < max_page; i++, offset++) {