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")
Signed-off-by: Sarthak Kukreti <sarthakkukr...@chromium.org>
---
 block/fops.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/block/fops.c b/block/fops.c
index d2e6be4e3d1c..2fd7e8b9ab48 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -648,25 +648,27 @@ 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->f_mode, 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 = blkdev_issue_zeroout(bdev, start >> SECTOR_SHIFT,
+               error = truncate_bdev_range(bdev, file->f_mode, start, end) ||
+                       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 = blkdev_issue_zeroout(bdev, start >> SECTOR_SHIFT,
+               error = truncate_bdev_range(bdev, file->f_mode, start, end) ||
+                       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 = blkdev_issue_discard(bdev, start >> SECTOR_SHIFT,
+               error = truncate_bdev_range(bdev, file->f_mode, start, end) ||
+                       blkdev_issue_discard(bdev, start >> SECTOR_SHIFT,
                                             len >> SECTOR_SHIFT, GFP_KERNEL);
                break;
        default:
-- 
2.40.0.634.g4ca3ef3211-goog

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