[PATCH v2 5/7] buffer: Fix various functions for block size > PAGE_SIZE

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

If i_blkbits is larger than PAGE_SHIFT, we shift by a negative number,
which is undefined.  It is safe to shift the block left as a block
device must be smaller than MAX_LFS_FILESIZE, which is guaranteed to
fit in loff_t.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Pankaj Raghav <p.raghav@samsung.com>
---
 fs/buffer.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index ab345fd4da12..faf1916200c2 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -199,7 +199,7 @@ __find_get_block_slow(struct block_device *bdev, sector_t block)
 	int all_mapped = 1;
 	static DEFINE_RATELIMIT_STATE(last_warned, HZ, 1);
 
-	index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
+	index = ((loff_t)block << bd_inode->i_blkbits) / PAGE_SIZE;
 	folio = __filemap_get_folio(bd_mapping, index, FGP_ACCESSED, 0);
 	if (IS_ERR(folio))
 		goto out;
@@ -1693,13 +1693,13 @@ void clean_bdev_aliases(struct block_device *bdev, sector_t block, sector_t len)
 	struct inode *bd_inode = bdev->bd_inode;
 	struct address_space *bd_mapping = bd_inode->i_mapping;
 	struct folio_batch fbatch;
-	pgoff_t index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
+	pgoff_t index = ((loff_t)block << bd_inode->i_blkbits) / PAGE_SIZE;
 	pgoff_t end;
 	int i, count;
 	struct buffer_head *bh;
 	struct buffer_head *head;
 
-	end = (block + len - 1) >> (PAGE_SHIFT - bd_inode->i_blkbits);
+	end = ((loff_t)(block + len - 1) << bd_inode->i_blkbits) / PAGE_SIZE;
 	folio_batch_init(&fbatch);
 	while (filemap_get_folios(bd_mapping, &index, end, &fbatch)) {
 		count = folio_batch_count(&fbatch);
@@ -2660,8 +2660,8 @@ int block_truncate_page(struct address_space *mapping,
 		return 0;
 
 	length = blocksize - length;
-	iblock = (sector_t)index << (PAGE_SHIFT - inode->i_blkbits);
-	
+	iblock = ((loff_t)index * PAGE_SIZE) >> inode->i_blkbits;
+
 	folio = filemap_grab_folio(mapping, index);
 	if (IS_ERR(folio))
 		return PTR_ERR(folio);
-- 
2.42.0