btrfs: use memzero_page() instead of open coded kmap pattern

There are many places where kmap/memset/kunmap patterns occur.

Use the newly lifted memzero_page() to eliminate direct uses of kmap and
leverage the new core functions use of kmap_local_page().

The development of this patch was aided by the following coccinelle
script:

// <smpl>
// SPDX-License-Identifier: GPL-2.0-only
// Find kmap/memset/kunmap pattern and replace with memset*page calls
//
// NOTE: Offsets and other expressions may be more complex than what the script
// will automatically generate. Therefore a catchall rule is provided to find
// the pattern which then must be evaluated by hand.
//
// Confidence: Low
// Copyright: (C) 2021 Intel Corporation
// URL: http://coccinelle.lip6.fr/
// Comments:
// Options:

//
// Then the memset pattern
//
@ memset_rule1 @
expression page, V, L, Off;
identifier ptr;
type VP;
@@

(
-VP ptr = kmap(page);
|
-ptr = kmap(page);
|
-VP ptr = kmap_atomic(page);
|
-ptr = kmap_atomic(page);
)
<+...
(
-memset(ptr, 0, L);
+memzero_page(page, 0, L);
|
-memset(ptr + Off, 0, L);
+memzero_page(page, Off, L);
|
-memset(ptr, V, L);
+memset_page(page, V, 0, L);
|
-memset(ptr + Off, V, L);
+memset_page(page, V, Off, L);
)
...+>
(
-kunmap(page);
|
-kunmap_atomic(ptr);
)

// Remove any pointers left unused
@
depends on memset_rule1
@
identifier memset_rule1.ptr;
type VP, VP1;
@@

-VP ptr;
... when != ptr;
? VP1 ptr;

//
// Catch all
//
@ memset_rule2 @
expression page;
identifier ptr;
expression GenTo, GenSize, GenValue;
type VP;
@@

(
-VP ptr = kmap(page);
|
-ptr = kmap(page);
|
-VP ptr = kmap_atomic(page);
|
-ptr = kmap_atomic(page);
)
<+...
(
//
// Some call sites have complex expressions within the memset/memcpy
// The follow are catch alls which need to be evaluated by hand.
//
-memset(GenTo, 0, GenSize);
+memzero_pageExtra(page, GenTo, GenSize);
|
-memset(GenTo, GenValue, GenSize);
+memset_pageExtra(page, GenValue, GenTo, GenSize);
)
...+>
(
-kunmap(page);
|
-kunmap_atomic(ptr);
)

// Remove any pointers left unused
@
depends on memset_rule2
@
identifier memset_rule2.ptr;
type VP, VP1;
@@

-VP ptr;
... when != ptr;
? VP1 ptr;

// </smpl>

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ira Weiny <[e-mail]>
Reviewed-by: David Sterba <[e-mail]>
Cc: Alexander Viro <[e-mail]>
Cc: Chaitanya Kulkarni <[e-mail]>
Cc: Chris Mason <[e-mail]>
Cc: Josef Bacik <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/btrfs/compression.c

···
 		free_extent_map(em);
 
 		if (page->index == end_index) {
-			char *userpage;
 			size_t zero_offset = offset_in_page(isize);
 
 			if (zero_offset) {
 				int zeros;
 				zeros = PAGE_SIZE - zero_offset;
-				userpage = kmap_atomic(page);
-				memset(userpage + zero_offset, 0, zeros);
+				memzero_page(page, zero_offset, zeros);
 				flush_dcache_page(page);
-				kunmap_atomic(userpage);
 			}
 		}
 

fs/btrfs/extent_io.c

···
 	}
 
 	if (page->index == last_byte >> PAGE_SHIFT) {
-		char *userpage;
 		size_t zero_offset = offset_in_page(last_byte);
 
 		if (zero_offset) {
 			iosize = PAGE_SIZE - zero_offset;
-			userpage = kmap_atomic(page);
-			memset(userpage + zero_offset, 0, iosize);
+			memzero_page(page, zero_offset, iosize);
 			flush_dcache_page(page);
-			kunmap_atomic(userpage);
 		}
 	}
 	begin_page_read(fs_info, page);
···
 		u64 disk_bytenr;
 
 		if (cur >= last_byte) {
-			char *userpage;
 			struct extent_state *cached = NULL;
 
 			iosize = PAGE_SIZE - pg_offset;
-			userpage = kmap_atomic(page);
-			memset(userpage + pg_offset, 0, iosize);
+			memzero_page(page, pg_offset, iosize);
 			flush_dcache_page(page);
-			kunmap_atomic(userpage);
 			set_extent_uptodate(tree, cur, cur + iosize - 1,
 					    &cached, GFP_NOFS);
 			unlock_extent_cached(tree, cur,
···
 
 		/* we've found a hole, just zero and go on */
 		if (block_start == EXTENT_MAP_HOLE) {
-			char *userpage;
 			struct extent_state *cached = NULL;
 
-			userpage = kmap_atomic(page);
-			memset(userpage + pg_offset, 0, iosize);
+			memzero_page(page, pg_offset, iosize);
 			flush_dcache_page(page);
-			kunmap_atomic(userpage);
 
 			set_extent_uptodate(tree, cur, cur + iosize - 1,
 					    &cached, GFP_NOFS);
···
 	}
 
 	if (page->index == end_index) {
-		char *userpage;
-
-		userpage = kmap_atomic(page);
-		memset(userpage + pg_offset, 0,
-		       PAGE_SIZE - pg_offset);
-		kunmap_atomic(userpage);
+		memzero_page(page, pg_offset, PAGE_SIZE - pg_offset);
 		flush_dcache_page(page);
 	}
 

fs/btrfs/inode.c

···
 		if (!ret) {
 			unsigned long offset = offset_in_page(total_compressed);
 			struct page *page = pages[nr_pages - 1];
-			char *kaddr;
 
 			/* zero the tail end of the last page, we might be
 			 * sending it down to disk
 			 */
-			if (offset) {
-				kaddr = kmap_atomic(page);
-				memset(kaddr + offset, 0,
-				       PAGE_SIZE - offset);
-				kunmap_atomic(kaddr);
-			}
+			if (offset)
+				memzero_page(page, offset, PAGE_SIZE - offset);
 			will_compress = 1;
 		}
 	}
···
 	struct btrfs_ordered_extent *ordered;
 	struct extent_state *cached_state = NULL;
 	struct extent_changeset *data_reserved = NULL;
-	char *kaddr;
 	bool only_release_metadata = false;
 	u32 blocksize = fs_info->sectorsize;
 	pgoff_t index = from >> PAGE_SHIFT;
···
 	if (offset != blocksize) {
 		if (!len)
 			len = blocksize - offset;
-		kaddr = kmap(page);
 		if (front)
-			memset(kaddr + (block_start - page_offset(page)),
-				0, offset);
+			memzero_page(page, (block_start - page_offset(page)),
+				     offset);
 		else
-			memset(kaddr + (block_start - page_offset(page)) +  offset,
-				0, len);
+			memzero_page(page, (block_start - page_offset(page)) + offset,
+				     len);
 		flush_dcache_page(page);
-		kunmap(page);
 	}
 	ClearPageChecked(page);
 	set_page_dirty(page);
···
 	 * cover that region here.
 	 */
 
-	if (max_size + pg_offset < PAGE_SIZE) {
-		char *map = kmap(page);
-		memset(map + pg_offset + max_size, 0, PAGE_SIZE - max_size - pg_offset);
-		kunmap(page);
-	}
+	if (max_size + pg_offset < PAGE_SIZE)
+		memzero_page(page,  pg_offset + max_size,
+			     PAGE_SIZE - max_size - pg_offset);
 	kfree(tmp);
 	return ret;
 }
···
 	struct btrfs_ordered_extent *ordered;
 	struct extent_state *cached_state = NULL;
 	struct extent_changeset *data_reserved = NULL;
-	char *kaddr;
 	unsigned long zero_start;
 	loff_t size;
 	vm_fault_t ret;
···
 		zero_start = PAGE_SIZE;
 
 	if (zero_start != PAGE_SIZE) {
-		kaddr = kmap(page);
-		memset(kaddr + zero_start, 0, PAGE_SIZE - zero_start);
+		memzero_page(page, zero_start, PAGE_SIZE - zero_start);
 		flush_dcache_page(page);
-		kunmap(page);
 	}
 	ClearPageChecked(page);
 	set_page_dirty(page);

fs/btrfs/reflink.c

···
 	 * So what's in the range [500, 4095] corresponds to zeroes.
 	 */
 	if (datal < block_size) {
-		char *map;
-
-		map = kmap(page);
-		memset(map + datal, 0, block_size - datal);
+		memzero_page(page, datal, block_size - datal);
 		flush_dcache_page(page);
-		kunmap(page);
 	}
 
 	SetPageUptodate(page);

fs/btrfs/zlib.c

···
 	unsigned long bytes_left;
 	unsigned long total_out = 0;
 	unsigned long pg_offset = 0;
-	char *kaddr;
 
 	destlen = min_t(unsigned long, destlen, PAGE_SIZE);
 	bytes_left = destlen;
···
 	 * end of the inline extent (destlen) to the end of the page
 	 */
 	if (pg_offset < destlen) {
-		kaddr = kmap_atomic(dest_page);
-		memset(kaddr + pg_offset, 0, destlen - pg_offset);
-		kunmap_atomic(kaddr);
+		memzero_page(dest_page, pg_offset, destlen - pg_offset);
 	}
 	return ret;
 }

fs/btrfs/zstd.c

···
 	size_t ret2;
 	unsigned long total_out = 0;
 	unsigned long pg_offset = 0;
-	char *kaddr;
 
 	stream = ZSTD_initDStream(
 			ZSTD_BTRFS_MAX_INPUT, workspace->mem, workspace->size);
···
 	ret = 0;
 finish:
 	if (pg_offset < destlen) {
-		kaddr = kmap_atomic(dest_page);
-		memset(kaddr + pg_offset, 0, destlen - pg_offset);
-		kunmap_atomic(kaddr);
+		memzero_page(dest_page, pg_offset, destlen - pg_offset);
 	}
 	return ret;
 }