[PATCH] block: Don't invalidate pagecache for invalid falloc modes

[Sarthak Kukreti]

Only call truncate_bdev_range() if the fallocate mode is
supported. This fixes a bug where data in the pagecache
could be invalidated if the fallocate() was called on the
block device with an invalid mode.

Fixes: 25f4c41415e5 ("block: implement (some of) fallocate for block devices")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Darrick J. Wong <djwong@xxxxxxxxxx>
Signed-off-by: Sarthak Kukreti <sarthakkukreti@xxxxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
---
 block/fops.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/block/fops.c b/block/fops.c
index acff3d5d22d4..73e42742543f 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -772,24 +772,35 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
 
 	filemap_invalidate_lock(inode->i_mapping);
 
-	/* Invalidate the page cache, including dirty pages. */
-	error = truncate_bdev_range(bdev, file_to_blk_mode(file), start, end);
-	if (error)
-		goto fail;
-
+	/*
+	 * Invalidate the page cache, including dirty pages, for valid
+	 * de-allocate mode calls to fallocate().
+	 */
 	switch (mode) {
 	case FALLOC_FL_ZERO_RANGE:
 	case FALLOC_FL_ZERO_RANGE | FALLOC_FL_KEEP_SIZE:
+		error = truncate_bdev_range(bdev, file_to_blk_mode(file), start, end);
+		if (error)
+			goto fail;
+
 		error = blkdev_issue_zeroout(bdev, start >> SECTOR_SHIFT,
 					     len >> SECTOR_SHIFT, GFP_KERNEL,
 					     BLKDEV_ZERO_NOUNMAP);
 		break;
 	case FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE:
+		error = truncate_bdev_range(bdev, file_to_blk_mode(file), start, end);
+		if (error)
+			goto fail;
+
 		error = blkdev_issue_zeroout(bdev, start >> SECTOR_SHIFT,
 					     len >> SECTOR_SHIFT, GFP_KERNEL,
 					     BLKDEV_ZERO_NOFALLBACK);
 		break;
 	case FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE | FALLOC_FL_NO_HIDE_STALE:
+		error = truncate_bdev_range(bdev, file_to_blk_mode(file), start, end);
+		if (error)
+			goto fail;
+
 		error = blkdev_issue_discard(bdev, start >> SECTOR_SHIFT,
 					     len >> SECTOR_SHIFT, GFP_KERNEL);
 		break;
-- 
2.42.0.609.gbb76f46606-goog