blkcg: remove blkio_group->path[]

blkio_group->path[] stores the path of the associated cgroup and is
used only for debug messages.  Just format the path from blkg->cgroup
when printing debug messages.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-cgroup.c

@@ -114,7 +114,6 @@ static struct blkio_group *blkg_alloc(struct blkio_cgroup *blkcg,
 	INIT_LIST_HEAD(&blkg->q_node);
 	blkg->blkcg = blkcg;
 	blkg->refcnt = 1;
-	cgroup_path(blkcg->css.cgroup, blkg->path, sizeof(blkg->path));
 
 	for (i = 0; i < BLKCG_MAX_POLS; i++) {
 		struct blkio_policy_type *pol = blkio_policy[i];

block/blk-cgroup.h

@@ -77,8 +77,6 @@ struct blkio_group {
 	struct list_head q_node;
 	struct hlist_node blkcg_node;
 	struct blkio_cgroup *blkcg;
-	/* Store cgroup path */
-	char path[128];
 	/* reference count */
 	int refcnt;
 
@@ -167,9 +165,24 @@ static inline struct blkio_group *pdata_to_blkg(void *pdata)
 	return NULL;
 }
 
-static inline char *blkg_path(struct blkio_group *blkg)
+/**
+ * blkg_path - format cgroup path of blkg
+ * @blkg: blkg of interest
+ * @buf: target buffer
+ * @buflen: target buffer length
+ *
+ * Format the path of the cgroup of @blkg into @buf.
+ */
+static inline int blkg_path(struct blkio_group *blkg, char *buf, int buflen)
 {
-	return blkg->path;
+	int ret;
+
+	rcu_read_lock();
+	ret = cgroup_path(blkg->blkcg->css.cgroup, buf, buflen);
+	rcu_read_unlock();
+	if (ret)
+		strncpy(buf, "<unavailable>", buflen);
+	return ret;
 }
 
 /**

block/blk-throttle.c

@@ -155,9 +155,12 @@ static inline int throtl_tg_##name(const struct throtl_grp *tg)		\
 
 THROTL_TG_FNS(on_rr);
 
-#define throtl_log_tg(td, tg, fmt, args...)				\
-	blk_add_trace_msg((td)->queue, "throtl %s " fmt,		\
-			  blkg_path(tg_to_blkg(tg)), ##args);		\
+#define throtl_log_tg(td, tg, fmt, args...)	do {			\
+	char __pbuf[128];						\
+									\
+	blkg_path(tg_to_blkg(tg), __pbuf, sizeof(__pbuf));		\
+	blk_add_trace_msg((td)->queue, "throtl %s " fmt, __pbuf, ##args); \
+} while (0)
 
 #define throtl_log(td, fmt, args...)	\
 	blk_add_trace_msg((td)->queue, "throtl " fmt, ##args)

block/cfq-iosched.c

@@ -573,14 +573,21 @@ static inline void cfqg_put(struct cfq_group *cfqg)
 	return blkg_put(cfqg_to_blkg(cfqg));
 }
 
-#define cfq_log_cfqq(cfqd, cfqq, fmt, args...)	\
+#define cfq_log_cfqq(cfqd, cfqq, fmt, args...)	do {			\
+	char __pbuf[128];						\
+									\
+	blkg_path(cfqg_to_blkg((cfqq)->cfqg), __pbuf, sizeof(__pbuf));	\
 	blk_add_trace_msg((cfqd)->queue, "cfq%d%c %s " fmt, (cfqq)->pid, \
-			cfq_cfqq_sync((cfqq)) ? 'S' : 'A', \
-			blkg_path(cfqg_to_blkg((cfqq)->cfqg)), ##args)
-
-#define cfq_log_cfqg(cfqd, cfqg, fmt, args...)				\
-	blk_add_trace_msg((cfqd)->queue, "%s " fmt,			\
-			blkg_path(cfqg_to_blkg((cfqg))), ##args)	\
+			  cfq_cfqq_sync((cfqq)) ? 'S' : 'A',		\
+			  __pbuf, ##args);				\
+} while (0)
+
+#define cfq_log_cfqg(cfqd, cfqg, fmt, args...)	do {			\
+	char __pbuf[128];						\
+									\
+	blkg_path(cfqg_to_blkg(cfqg), __pbuf, sizeof(__pbuf));		\
+	blk_add_trace_msg((cfqd)->queue, "%s " fmt, __pbuf, ##args);	\
+} while (0)
 
 static inline void cfqg_stats_update_io_add(struct cfq_group *cfqg,
 					    struct cfq_group *curr_cfqg, int rw)