btrfs: compression: add error handling for missed page cache

For all the supported compression algorithms, the compression path would
always need to grab the page cache, then do the compression.

Normally we would get a page reference without any problem, since the
write path should have already locked the pages in the write range.
For the sake of error handling, we should handle the page cache miss
case.

Adds a common wrapper, btrfs_compress_find_get_page(), which calls
find_get_page(), and do the error handling along with an error message.

Callers inside compression path would only need to call
btrfs_compress_find_get_page(), and error out if it returned any error.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/compression.c

@@ -974,6 +974,29 @@ static unsigned int btrfs_compress_set_level(int type, unsigned level)
 	return level;
 }
 
+/* Wrapper around find_get_page(), with extra error message. */
+int btrfs_compress_find_get_page(struct address_space *mapping, u64 start,
+				 struct page **in_page_ret)
+{
+	struct page *in_page;
+
+	/*
+	 * The compressed write path should have the page locked already, thus
+	 * we only need to grab one reference of the page cache.
+	 */
+	in_page = find_get_page(mapping, start >> PAGE_SHIFT);
+	if (unlikely(!in_page)) {
+		struct btrfs_inode *inode = BTRFS_I(mapping->host);
+
+		btrfs_crit(inode->root->fs_info,
+		"failed to get page cache, root %lld ino %llu file offset %llu",
+			   inode->root->root_key.objectid, btrfs_ino(inode), start);
+		return -ENOENT;
+	}
+	*in_page_ret = in_page;
+	return 0;
+}
+
 /*
  * Given an address space and start and length, compress the bytes into @pages
  * that are allocated on demand.

fs/btrfs/compression.h

@@ -149,6 +149,9 @@ bool btrfs_compress_is_valid_type(const char *str, size_t len);
 
 int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end);
 
+int btrfs_compress_find_get_page(struct address_space *mapping, u64 start,
+				 struct page **in_page_ret);
+
 int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
 		u64 start, struct page **pages, unsigned long *out_pages,
 		unsigned long *total_in, unsigned long *total_out);

fs/btrfs/lzo.c

@@ -244,8 +244,9 @@ int lzo_compress_pages(struct list_head *ws, struct address_space *mapping,
 
 		/* Get the input page first */
 		if (!page_in) {
-			page_in = find_get_page(mapping, cur_in >> PAGE_SHIFT);
-			ASSERT(page_in);
+			ret =  btrfs_compress_find_get_page(mapping, cur_in, &page_in);
+			if (ret < 0)
+				goto out;
 		}
 
 		/* Compress at most one sector of data each time */

fs/btrfs/zlib.c

@@ -151,9 +151,12 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
 					if (data_in) {
 						kunmap_local(data_in);
 						put_page(in_page);
+						data_in = NULL;
 					}
-					in_page = find_get_page(mapping,
-								start >> PAGE_SHIFT);
+					ret = btrfs_compress_find_get_page(mapping,
+							start, &in_page);
+					if (ret < 0)
+						goto out;
 					data_in = kmap_local_page(in_page);
 					copy_page(workspace->buf + i * PAGE_SIZE,
 						  data_in);
@@ -164,9 +167,12 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
 				if (data_in) {
 					kunmap_local(data_in);
 					put_page(in_page);
+					data_in = NULL;
 				}
-				in_page = find_get_page(mapping,
-							start >> PAGE_SHIFT);
+				ret = btrfs_compress_find_get_page(mapping,
+						start, &in_page);
+				if (ret < 0)
+					goto out;
 				data_in = kmap_local_page(in_page);
 				start += PAGE_SIZE;
 				workspace->strm.next_in = data_in;

fs/btrfs/zstd.c

@@ -406,7 +406,9 @@ int zstd_compress_pages(struct list_head *ws, struct address_space *mapping,
 	}
 
 	/* map in the first page of input data */
-	in_page = find_get_page(mapping, start >> PAGE_SHIFT);
+	ret = btrfs_compress_find_get_page(mapping, start, &in_page);
+	if (ret < 0)
+		goto out;
 	workspace->in_buf.src = kmap_local_page(in_page);
 	workspace->in_buf.pos = 0;
 	workspace->in_buf.size = min_t(size_t, len, PAGE_SIZE);
@@ -479,10 +481,13 @@ int zstd_compress_pages(struct list_head *ws, struct address_space *mapping,
 		if (workspace->in_buf.pos == workspace->in_buf.size) {
 			tot_in += PAGE_SIZE;
 			kunmap_local(workspace->in_buf.src);
+			workspace->in_buf.src = NULL;
 			put_page(in_page);
 			start += PAGE_SIZE;
 			len -= PAGE_SIZE;
-			in_page = find_get_page(mapping, start >> PAGE_SHIFT);
+			ret = btrfs_compress_find_get_page(mapping, start, &in_page);
+			if (ret < 0)
+				goto out;
 			workspace->in_buf.src = kmap_local_page(in_page);
 			workspace->in_buf.pos = 0;
 			workspace->in_buf.size = min_t(size_t, len, PAGE_SIZE);