btrfs: compression: inline alloc_workspace

Replace indirect calls to alloc_workspace by switch and calls to the
specific callbacks. This is mainly to get rid of the indirection due to
spectre vulnerability mitigations.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/compression.c

@@ -912,7 +912,6 @@ static struct list_head *alloc_heuristic_ws(unsigned int level)
 
 const struct btrfs_compress_op btrfs_heuristic_compress = {
 	.workspace_manager = &heuristic_wsm,
-	.alloc_workspace = alloc_heuristic_ws,
 	.free_workspace = free_heuristic_ws,
 };
 
@@ -924,6 +923,22 @@ static const struct btrfs_compress_op * const btrfs_compress_op[] = {
 	&btrfs_zstd_compress,
 };
 
+static struct list_head *alloc_workspace(int type, unsigned int level)
+{
+	switch (type) {
+	case BTRFS_COMPRESS_NONE: return alloc_heuristic_ws(level);
+	case BTRFS_COMPRESS_ZLIB: return zlib_alloc_workspace(level);
+	case BTRFS_COMPRESS_LZO:  return lzo_alloc_workspace(level);
+	case BTRFS_COMPRESS_ZSTD: return zstd_alloc_workspace(level);
+	default:
+		/*
+		 * This can't happen, the type is validated several times
+		 * before we get here.
+		 */
+		BUG();
+	}
+}
+
 static void btrfs_init_workspace_manager(int type)
 {
 	const struct btrfs_compress_op *ops = btrfs_compress_op[type];
@@ -941,7 +956,7 @@ static void btrfs_init_workspace_manager(int type)
 	 * Preallocate one workspace for each compression type so we can
 	 * guarantee forward progress in the worst case
 	 */
-	workspace = wsm->ops->alloc_workspace(0);
+	workspace = alloc_workspace(type, 0);
 	if (IS_ERR(workspace)) {
 		pr_warn(
 	"BTRFS: cannot preallocate compression workspace, will try later\n");
@@ -1020,7 +1035,7 @@ struct list_head *btrfs_get_workspace(int type, unsigned int level)
 	 * context of btrfs_compress_bio/btrfs_compress_pages
 	 */
 	nofs_flag = memalloc_nofs_save();
-	workspace = wsm->ops->alloc_workspace(level);
+	workspace = alloc_workspace(type, level);
 	memalloc_nofs_restore(nofs_flag);
 
 	if (IS_ERR(workspace)) {

fs/btrfs/compression.h

@@ -124,8 +124,6 @@ struct list_head *btrfs_get_workspace(int type, unsigned int level);
 void btrfs_put_workspace(struct workspace_manager *wsm, struct list_head *ws);
 
 struct btrfs_compress_op {
-	struct list_head *(*alloc_workspace)(unsigned int level);
-
 	void (*free_workspace)(struct list_head *workspace);
 
 	struct workspace_manager *workspace_manager;

fs/btrfs/lzo.c

@@ -484,7 +484,6 @@ int lzo_decompress(struct list_head *ws, unsigned char *data_in,
 
 const struct btrfs_compress_op btrfs_lzo_compress = {
 	.workspace_manager	= &wsm,
-	.alloc_workspace	= lzo_alloc_workspace,
 	.free_workspace		= lzo_free_workspace,
 	.max_level		= 1,
 	.default_level		= 1,

fs/btrfs/zlib.c

@@ -400,7 +400,6 @@ int zlib_decompress(struct list_head *ws, unsigned char *data_in,
 
 const struct btrfs_compress_op btrfs_zlib_compress = {
 	.workspace_manager	= &wsm,
-	.alloc_workspace	= zlib_alloc_workspace,
 	.free_workspace		= zlib_free_workspace,
 	.max_level		= 9,
 	.default_level		= BTRFS_ZLIB_DEFAULT_LEVEL,

fs/btrfs/zstd.c

@@ -708,7 +708,6 @@ int zstd_decompress(struct list_head *ws, unsigned char *data_in,
 const struct btrfs_compress_op btrfs_zstd_compress = {
 	/* ZSTD uses own workspace manager */
 	.workspace_manager = NULL,
-	.alloc_workspace = zstd_alloc_workspace,
 	.free_workspace = zstd_free_workspace,
 	.max_level	= ZSTD_BTRFS_MAX_LEVEL,
 	.default_level	= ZSTD_BTRFS_DEFAULT_LEVEL,