[PATCH 1/2] hfsplus: release preallocated blocks in hfsplus_file_truncate()

[Viacheslav Dubeyko]

hfsplus_get_block() extends a fork through hfsplus_file_extend(),
which allocates whole clumps. Also, hfsplus_inode_read_fork()
initializes alloc_blocks from the on-disk total_blocks of the
fork, while i_size and phys_size are set to the logical size.
As a result, alloc_blocks can be ahead of the number of blocks
really needed to hold i_size, even when phys_size matches i_size.

hfsplus_file_truncate() returns early whenever i_size equals
phys_size, before it compares the required block count with
alloc_blocks. So, for example, a file whose size is aligned on
the block size keeps its clump preallocation after the last
close. Moreover, hfsplus_delete_cat() does not free the data
fork and relies on hfsplus_delete_inode() truncating the file
to zero size. If a file has zero logical size but allocated
blocks, the early return skips the truncation, and its blocks
remain marked as used in the allocation file after the file
has been deleted.

Compute the required block count first and return early only
when neither the size nor the allocation needs to be trimmed.
This keeps the intent of the original early return of not
dirtying an unchanged inode. The existing logic further down
already handles the case of blk_cnt being equal to alloc_blocks.

Fixes: f76d28d235cf ("[PATCH] hfs: don't dirty unchanged inode")
cc: John Paul Adrian Glaubitz <glaubitz@xxxxxxxxxxxxxxxxxxx>
cc: Yangtao Li <frank.li@xxxxxxxx>
cc: linux-fsdevel@xxxxxxxxxxxxxxx
Signed-off-by: Viacheslav Dubeyko <slava@xxxxxxxxxxx>
---
 fs/hfsplus/extents.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/fs/hfsplus/extents.c b/fs/hfsplus/extents.c
index eb7c11524d18..924941440066 100644
--- a/fs/hfsplus/extents.c
+++ b/fs/hfsplus/extents.c
@@ -570,12 +570,19 @@ void hfsplus_file_truncate(struct inode *inode)
 			return;
 		mark_inode_dirty(inode);
 		return;
-	} else if (inode->i_size == hip->phys_size)
-		return;
+	}
 
 	blk_cnt = (inode->i_size + HFSPLUS_SB(sb)->alloc_blksz - 1) >>
 			HFSPLUS_SB(sb)->alloc_blksz_shift;
 
+	/*
+	 * hfsplus_file_extend() allocates whole clumps, so alloc_blocks can
+	 * be ahead of phys_size even when phys_size matches i_size. Return
+	 * early only if neither the size nor the allocation needs trimming.
+	 */
+	if (inode->i_size == hip->phys_size && blk_cnt == hip->alloc_blocks)
+		return;
+
 	mutex_lock(&hip->extents_lock);
 
 	alloc_cnt = hip->alloc_blocks;
-- 
2.43.0