btrfs: convert kmap to kmap_local_page, simple cases

Use a simple coccinelle script to help convert the most common
kmap()/kunmap() patterns to kmap_local_page()/kunmap_local().

Note that some kmaps which were caught by this script needed to be
handled by hand because of the strict unmapping order of kunmap_local()
so they are not included in this patch.  But this script got us started.

There's another temp variable added for the final length write to the
first page so it does not interfere with cpage_out that is used for
mapping other pages.

The development of this patch was aided by the follow script:

// <smpl>
// SPDX-License-Identifier: GPL-2.0-only
// Find kmap and replace with kmap_local_page then mark kunmap
//
// Confidence: Low
// Copyright: (C) 2021 Intel Corporation
// URL: http://coccinelle.lip6.fr/

@ catch_all @
expression e, e2;
@@

(
-kmap(e)
+kmap_local_page(e)
)
...
(
-kunmap(...)
+kunmap_local()
)

// </smpl>

Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 3f4c832abfed..2600703fab83 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -1611,7 +1611,7 @@ static void heuristic_collect_sample(struct inode *inode, u64 start, u64 end,
 	curr_sample_pos = 0;
 	while (index < index_end) {
 		page = find_get_page(inode->i_mapping, index);
-		in_data = kmap(page);
+		in_data = kmap_local_page(page);
 		/* Handle case where the start is not aligned to PAGE_SIZE */
 		i = start % PAGE_SIZE;
 		while (i < PAGE_SIZE - SAMPLING_READ_SIZE) {
@@ -1624,7 +1624,7 @@ static void heuristic_collect_sample(struct inode *inode, u64 start, u64 end,
 			start += SAMPLING_INTERVAL;
 			curr_sample_pos += SAMPLING_READ_SIZE;
 		}
-		kunmap(page);
+		kunmap_local(in_data);
 		put_page(page);
 
 		index++;