blk-cgroup: replace bio_blkcg with bio_blkcg_css

All callers of bio_blkcg actually want the CSS, so replace it with an
interface that does return the CSS.  This now allows to move
struct blkcg_gq to block/blk-cgroup.h instead of exposing it in a
public header.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20220420042723.1010598-10-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Christoph Hellwig

block/blk-cgroup.c

@@ -155,6 +155,22 @@ static void blkg_async_bio_workfn(struct work_struct *work)
 		blk_finish_plug(&plug);
 }
 
+/**
+ * bio_blkcg_css - return the blkcg CSS associated with a bio
+ * @bio: target bio
+ *
+ * This returns the CSS for the blkcg associated with a bio, or %NULL if not
+ * associated. Callers are expected to either handle %NULL or know association
+ * has been done prior to calling this.
+ */
+struct cgroup_subsys_state *bio_blkcg_css(struct bio *bio)
+{
+	if (!bio || !bio->bi_blkg)
+		return NULL;
+	return &bio->bi_blkg->blkcg->css;
+}
+EXPORT_SYMBOL_GPL(bio_blkcg_css);
+
 /**
  * blkcg_parent - get the parent of a blkcg
  * @blkcg: blkcg of interest
@@ -1938,7 +1954,7 @@ void bio_associate_blkg(struct bio *bio)
 	rcu_read_lock();
 
 	if (bio->bi_blkg)
-		css = &bio_blkcg(bio)->css;
+		css = bio_blkcg_css(bio);
 	else
 		css = blkcg_css();
 

block/blk-cgroup.h

@@ -25,6 +25,64 @@ struct blkg_policy_data;
 #define BLKG_STAT_CPU_BATCH	(INT_MAX / 2)
 
 #ifdef CONFIG_BLK_CGROUP
+
+enum blkg_iostat_type {
+	BLKG_IOSTAT_READ,
+	BLKG_IOSTAT_WRITE,
+	BLKG_IOSTAT_DISCARD,
+
+	BLKG_IOSTAT_NR,
+};
+
+struct blkg_iostat {
+	u64				bytes[BLKG_IOSTAT_NR];
+	u64				ios[BLKG_IOSTAT_NR];
+};
+
+struct blkg_iostat_set {
+	struct u64_stats_sync		sync;
+	struct blkg_iostat		cur;
+	struct blkg_iostat		last;
+};
+
+/* association between a blk cgroup and a request queue */
+struct blkcg_gq {
+	/* Pointer to the associated request_queue */
+	struct request_queue		*q;
+	struct list_head		q_node;
+	struct hlist_node		blkcg_node;
+	struct blkcg			*blkcg;
+
+	/* all non-root blkcg_gq's are guaranteed to have access to parent */
+	struct blkcg_gq			*parent;
+
+	/* reference count */
+	struct percpu_ref		refcnt;
+
+	/* is this blkg online? protected by both blkcg and q locks */
+	bool				online;
+
+	struct blkg_iostat_set __percpu	*iostat_cpu;
+	struct blkg_iostat_set		iostat;
+
+	struct blkg_policy_data		*pd[BLKCG_MAX_POLS];
+
+	spinlock_t			async_bio_lock;
+	struct bio_list			async_bios;
+	union {
+		struct work_struct	async_bio_work;
+		struct work_struct	free_work;
+	};
+
+	atomic_t			use_delay;
+	atomic64_t			delay_nsec;
+	atomic64_t			delay_start;
+	u64				last_delay;
+	int				last_use;
+
+	struct rcu_head			rcu_head;
+};
+
 struct blkcg {
 	struct cgroup_subsys_state	css;
 	spinlock_t			lock;
@@ -173,9 +231,9 @@ static inline struct cgroup_subsys_state *blkcg_css(void)
  *
  * In order to avoid priority inversions we sometimes need to issue a bio as if
  * it were attached to the root blkg, and then backcharge to the actual owning
- * blkg.  The idea is we do bio_blkcg() to look up the actual context for the
- * bio and attach the appropriate blkg to the bio.  Then we call this helper and
- * if it is true run with the root blkg for that queue and then do any
+ * blkg.  The idea is we do bio_blkcg_css() to look up the actual context for
+ * the bio and attach the appropriate blkg to the bio.  Then we call this helper
+ * and if it is true run with the root blkg for that queue and then do any
  * backcharging to the originating cgroup once the io is complete.
  */
 static inline bool bio_issue_as_root_blkg(struct bio *bio)
@@ -464,6 +522,9 @@ struct blkcg_policy_data {
 struct blkcg_policy {
 };
 
+struct blkcg {
+};
+
 #ifdef CONFIG_BLOCK
 
 static inline struct blkcg_gq *blkg_lookup(struct blkcg *blkcg, void *key) { return NULL; }

drivers/block/loop.c

@@ -1829,12 +1829,14 @@ static blk_status_t loop_queue_rq(struct blk_mq_hw_ctx *hctx,
 	cmd->blkcg_css = NULL;
 	cmd->memcg_css = NULL;
 #ifdef CONFIG_BLK_CGROUP
-	if (rq->bio && rq->bio->bi_blkg) {
-		cmd->blkcg_css = &bio_blkcg(rq->bio)->css;
+	if (rq->bio) {
+		cmd->blkcg_css = bio_blkcg_css(rq->bio);
 #ifdef CONFIG_MEMCG
-		cmd->memcg_css =
-			cgroup_get_e_css(cmd->blkcg_css->cgroup,
-					&memory_cgrp_subsys);
+		if (cmd->blkcg_css) {
+			cmd->memcg_css =
+				cgroup_get_e_css(cmd->blkcg_css->cgroup,
+						&memory_cgrp_subsys);
+		}
 #endif
 	}
 #endif

include/linux/blk-cgroup.h

@@ -28,102 +28,29 @@
 #define FC_APPID_LEN              129
 
 #ifdef CONFIG_BLK_CGROUP
-
-enum blkg_iostat_type {
-	BLKG_IOSTAT_READ,
-	BLKG_IOSTAT_WRITE,
-	BLKG_IOSTAT_DISCARD,
-
-	BLKG_IOSTAT_NR,
-};
-
-struct blkg_iostat {
-	u64				bytes[BLKG_IOSTAT_NR];
-	u64				ios[BLKG_IOSTAT_NR];
-};
-
-struct blkg_iostat_set {
-	struct u64_stats_sync		sync;
-	struct blkg_iostat		cur;
-	struct blkg_iostat		last;
-};
-
-/* association between a blk cgroup and a request queue */
-struct blkcg_gq {
-	/* Pointer to the associated request_queue */
-	struct request_queue		*q;
-	struct list_head		q_node;
-	struct hlist_node		blkcg_node;
-	struct blkcg			*blkcg;
-
-	/* all non-root blkcg_gq's are guaranteed to have access to parent */
-	struct blkcg_gq			*parent;
-
-	/* reference count */
-	struct percpu_ref		refcnt;
-
-	/* is this blkg online? protected by both blkcg and q locks */
-	bool				online;
-
-	struct blkg_iostat_set __percpu	*iostat_cpu;
-	struct blkg_iostat_set		iostat;
-
-	struct blkg_policy_data		*pd[BLKCG_MAX_POLS];
-
-	spinlock_t			async_bio_lock;
-	struct bio_list			async_bios;
-	union {
-		struct work_struct	async_bio_work;
-		struct work_struct	free_work;
-	};
-
-	atomic_t			use_delay;
-	atomic64_t			delay_nsec;
-	atomic64_t			delay_start;
-	u64				last_delay;
-	int				last_use;
-
-	struct rcu_head			rcu_head;
-};
-
 extern struct cgroup_subsys_state * const blkcg_root_css;
 
 void blkcg_schedule_throttle(struct request_queue *q, bool use_memdelay);
 void blkcg_maybe_throttle_current(void);
-
-/**
- * bio_blkcg - grab the blkcg associated with a bio
- * @bio: target bio
- *
- * This returns the blkcg associated with a bio, %NULL if not associated.
- * Callers are expected to either handle %NULL or know association has been
- * done prior to calling this.
- */
-static inline struct blkcg *bio_blkcg(struct bio *bio)
-{
-	if (bio && bio->bi_blkg)
-		return bio->bi_blkg->blkcg;
-	return NULL;
-}
-
 bool blk_cgroup_congested(void);
 void blkcg_pin_online(struct cgroup_subsys_state *blkcg_css);
 void blkcg_unpin_online(struct cgroup_subsys_state *blkcg_css);
 struct list_head *blkcg_get_cgwb_list(struct cgroup_subsys_state *css);
+struct cgroup_subsys_state *bio_blkcg_css(struct bio *bio);
 
 #else	/* CONFIG_BLK_CGROUP */
 
-struct blkcg_gq {
-};
-
 #define blkcg_root_css	((struct cgroup_subsys_state *)ERR_PTR(-EINVAL))
 
 static inline void blkcg_maybe_throttle_current(void) { }
 static inline bool blk_cgroup_congested(void) { return false; }
 
 #ifdef CONFIG_BLOCK
 static inline void blkcg_schedule_throttle(struct request_queue *q, bool use_memdelay) { }
-static inline struct blkcg *bio_blkcg(struct bio *bio) { return NULL; }
+static inline struct cgroup_subsys_state *bio_blkcg_css(struct bio *bio)
+{
+	return NULL;
+}
 #endif /* CONFIG_BLOCK */
 
 #endif	/* CONFIG_BLK_CGROUP */

kernel/trace/blktrace.c

@@ -783,16 +783,18 @@ void blk_trace_shutdown(struct request_queue *q)
 #ifdef CONFIG_BLK_CGROUP
 static u64 blk_trace_bio_get_cgid(struct request_queue *q, struct bio *bio)
 {
+	struct cgroup_subsys_state *blkcg_css;
 	struct blk_trace *bt;
 
 	/* We don't use the 'bt' value here except as an optimization... */
 	bt = rcu_dereference_protected(q->blk_trace, 1);
 	if (!bt || !(blk_tracer_flags.val & TRACE_BLK_OPT_CGROUP))
 		return 0;
 
-	if (!bio->bi_blkg)
+	blkcg_css = bio_blkcg_css(bio);
+	if (!blkcg_css)
 		return 0;
-	return cgroup_id(bio_blkcg(bio)->css.cgroup);
+	return cgroup_id(blkcg_css->cgroup);
 }
 #else
 static u64 blk_trace_bio_get_cgid(struct request_queue *q, struct bio *bio)