1 files changed, 83 insertions, 59 deletions
diff --git a/fs/exfat/inode.c b/fs/exfat/inode.c
index 96952d4acb50..b22c02d6000f 100644
--- a/fs/exfat/inode.c
+++ b/fs/exfat/inode.c
@@ -274,9 +274,11 @@ static int exfat_get_block(struct inode *inode, sector_t iblock,
 	sector_t last_block;
 	sector_t phys = 0;
 	sector_t valid_blks;
+	loff_t i_size;
 
 	mutex_lock(&sbi->s_lock);
-	last_block = EXFAT_B_TO_BLK_ROUND_UP(i_size_read(inode), sb);
+	i_size = i_size_read(inode);
+	last_block = EXFAT_B_TO_BLK_ROUND_UP(i_size, sb);
 	if (iblock >= last_block && !create)
 		goto done;
 
@@ -305,77 +307,99 @@ static int exfat_get_block(struct inode *inode, sector_t iblock,
 	if (buffer_delay(bh_result))
 		clear_buffer_delay(bh_result);
 
-	if (create) {
+	/*
+	 * In most cases, we just need to set bh_result to mapped, unmapped
+	 * or new status as follows:
+	 *  1. i_size == valid_size
+	 *  2. write case (create == 1)
+	 *  3. direct_read (!bh_result->b_folio)
+	 *     -> the unwritten part will be zeroed in exfat_direct_IO()
+	 *
+	 * Otherwise, in the case of buffered read, it is necessary to take
+	 * care the last nested block if valid_size is not equal to i_size.
+	 */
+	if (i_size == ei->valid_size || create || !bh_result->b_folio)
 		valid_blks = EXFAT_B_TO_BLK_ROUND_UP(ei->valid_size, sb);
+	else
+		valid_blks = EXFAT_B_TO_BLK(ei->valid_size, sb);
 
-		if (iblock + max_blocks < valid_blks) {
-			/* The range has been written, map it */
-			goto done;
-		} else if (iblock < valid_blks) {
-			/*
-			 * The range has been partially written,
-			 * map the written part.
-			 */
-			max_blocks = valid_blks - iblock;
-			goto done;
-		}
+	/* The range has been fully written, map it */
+	if (iblock + max_blocks < valid_blks)
+		goto done;
 
-		/* The area has not been written, map and mark as new. */
-		set_buffer_new(bh_result);
+	/* The range has been partially written, map the written part */
+	if (iblock < valid_blks) {
+		max_blocks = valid_blks - iblock;
+		goto done;
+	}
 
+	/* The area has not been written, map and mark as new for create case */
+	if (create) {
+		set_buffer_new(bh_result);
 		ei->valid_size = EXFAT_BLK_TO_B(iblock + max_blocks, sb);
 		mark_inode_dirty(inode);
-	} else {
-		valid_blks = EXFAT_B_TO_BLK(ei->valid_size, sb);
+		goto done;
+	}
 
-		if (iblock + max_blocks < valid_blks) {
-			/* The range has been written, map it */
+	/*
+	 * The area has just one block partially written.
+	 * In that case, we should read and fill the unwritten part of
+	 * a block with zero.
+	 */
+	if (bh_result->b_folio && iblock == valid_blks &&
+	    (ei->valid_size & (sb->s_blocksize - 1))) {
+		loff_t size, pos;
+		void *addr;
+
+		max_blocks = 1;
+
+		/*
+		 * No buffer_head is allocated.
+		 * (1) bmap: It's enough to set blocknr without I/O.
+		 * (2) read: The unwritten part should be filled with zero.
+		 *           If a folio does not have any buffers,
+		 *           let's returns -EAGAIN to fallback to
+		 *           block_read_full_folio() for per-bh IO.
+		 */
+		if (!folio_buffers(bh_result->b_folio)) {
+			err = -EAGAIN;
 			goto done;
-		} else if (iblock < valid_blks) {
-			/*
-			 * The area has been partially written,
-			 * map the written part.
-			 */
-			max_blocks = valid_blks - iblock;
+		}
+
+		pos = EXFAT_BLK_TO_B(iblock, sb);
+		size = ei->valid_size - pos;
+		addr = folio_address(bh_result->b_folio) +
+			offset_in_folio(bh_result->b_folio, pos);
+
+		/* Check if bh->b_data points to proper addr in folio */
+		if (bh_result->b_data != addr) {
+			exfat_fs_error_ratelimit(sb,
+					"b_data(%p) != folio_addr(%p)",
+					bh_result->b_data, addr);
+			err = -EINVAL;
 			goto done;
-		} else if (iblock == valid_blks &&
-			   (ei->valid_size & (sb->s_blocksize - 1))) {
-			/*
-			 * The block has been partially written,
-			 * zero the unwritten part and map the block.
-			 */
-			loff_t size, off, pos;
-
-			max_blocks = 1;
-
-			/*
-			 * For direct read, the unwritten part will be zeroed in
-			 * exfat_direct_IO()
-			 */
-			if (!bh_result->b_folio)
-				goto done;
-
-			pos = EXFAT_BLK_TO_B(iblock, sb);
-			size = ei->valid_size - pos;
-			off = pos & (PAGE_SIZE - 1);
-
-			folio_set_bh(bh_result, bh_result->b_folio, off);
-			err = bh_read(bh_result, 0);
-			if (err < 0)
-				goto unlock_ret;
-
-			folio_zero_segment(bh_result->b_folio, off + size,
-					off + sb->s_blocksize);
-		} else {
-			/*
-			 * The range has not been written, clear the mapped flag
-			 * to only zero the cache and do not read from disk.
-			 */
-			clear_buffer_mapped(bh_result);
 		}
+
+		/* Read a block */
+		err = bh_read(bh_result, 0);
+		if (err < 0)
+			goto done;
+
+		/* Zero unwritten part of a block */
+		memset(bh_result->b_data + size, 0, bh_result->b_size - size);
+		err = 0;
+		goto done;
 	}
+
+	/*
+	 * The area has not been written, clear mapped for read/bmap cases.
+	 * If so, it will be filled with zero without reading from disk.
+	 */
+	clear_buffer_mapped(bh_result);
 done:
 	bh_result->b_size = EXFAT_BLK_TO_B(max_blocks, sb);
+	if (err < 0)
+		clear_buffer_mapped(bh_result);
 unlock_ret:
 	mutex_unlock(&sbi->s_lock);
 	return err;