blk-cgroup: stop using seq_get_buf

seq_get_buf is a crutch that undoes all the memory safety of the
seq_file interface.  Use the normal seq_printf interfaces instead.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20210810152623.1796144-2-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-cgroup.c

@@ -877,8 +877,6 @@ static void blkcg_print_one_stat(struct blkcg_gq *blkg, struct seq_file *s)
 	bool has_stats = false;
 	const char *dname;
 	unsigned seq;
-	char *buf;
-	size_t size = seq_get_buf(s, &buf), off = 0;
 	int i;
 
 	if (!blkg->online)
@@ -888,13 +886,7 @@ static void blkcg_print_one_stat(struct blkcg_gq *blkg, struct seq_file *s)
 	if (!dname)
 		return;
 
-	/*
-	 * Hooray string manipulation, count is the size written NOT
-	 * INCLUDING THE \0, so size is now count+1 less than what we
-	 * had before, but we want to start writing the next bit from
-	 * the \0 so we only add count to buf.
-	 */
-	off += scnprintf(buf+off, size-off, "%s ", dname);
+	seq_printf(s, "%s ", dname);
 
 	do {
 		seq = u64_stats_fetch_begin(&bis->sync);
@@ -909,40 +901,30 @@ static void blkcg_print_one_stat(struct blkcg_gq *blkg, struct seq_file *s)
 
 	if (rbytes || wbytes || rios || wios) {
 		has_stats = true;
-		off += scnprintf(buf+off, size-off,
-			"rbytes=%llu wbytes=%llu rios=%llu wios=%llu dbytes=%llu dios=%llu",
+		seq_printf(s, "rbytes=%llu wbytes=%llu rios=%llu wios=%llu dbytes=%llu dios=%llu",
 			rbytes, wbytes, rios, wios,
 			dbytes, dios);
 	}
 
 	if (blkcg_debug_stats && atomic_read(&blkg->use_delay)) {
 		has_stats = true;
-		off += scnprintf(buf+off, size-off, " use_delay=%d delay_nsec=%llu",
+		seq_printf(s, " use_delay=%d delay_nsec=%llu",
 			atomic_read(&blkg->use_delay),
 			atomic64_read(&blkg->delay_nsec));
 	}
 
 	for (i = 0; i < BLKCG_MAX_POLS; i++) {
 		struct blkcg_policy *pol = blkcg_policy[i];
-		size_t written;
 
 		if (!blkg->pd[i] || !pol->pd_stat_fn)
 			continue;
 
-		written = pol->pd_stat_fn(blkg->pd[i], buf+off, size-off);
-		if (written)
+		if (pol->pd_stat_fn(blkg->pd[i], s))
 			has_stats = true;
-		off += written;
 	}
 
-	if (has_stats) {
-		if (off < size - 1) {
-			off += scnprintf(buf+off, size-off, "\n");
-			seq_commit(s, off);
-		} else {
-			seq_commit(s, -1);
-		}
-	}
+	if (has_stats)
+		seq_printf(s, "\n");
 }
 
 static int blkcg_print_stat(struct seq_file *sf, void *v)

block/blk-iocost.c

@@ -2988,34 +2988,29 @@ static void ioc_pd_free(struct blkg_policy_data *pd)
 	kfree(iocg);
 }
 
-static size_t ioc_pd_stat(struct blkg_policy_data *pd, char *buf, size_t size)
+static bool ioc_pd_stat(struct blkg_policy_data *pd, struct seq_file *s)
 {
 	struct ioc_gq *iocg = pd_to_iocg(pd);
 	struct ioc *ioc = iocg->ioc;
-	size_t pos = 0;
 
 	if (!ioc->enabled)
-		return 0;
+		return false;
 
 	if (iocg->level == 0) {
 		unsigned vp10k = DIV64_U64_ROUND_CLOSEST(
 			ioc->vtime_base_rate * 10000,
 			VTIME_PER_USEC);
-		pos += scnprintf(buf + pos, size - pos, " cost.vrate=%u.%02u",
-				  vp10k / 100, vp10k % 100);
+		seq_printf(s, " cost.vrate=%u.%02u", vp10k / 100, vp10k % 100);
 	}
 
-	pos += scnprintf(buf + pos, size - pos, " cost.usage=%llu",
-			 iocg->last_stat.usage_us);
+	seq_printf(s, " cost.usage=%llu", iocg->last_stat.usage_us);
 
 	if (blkcg_debug_stats)
-		pos += scnprintf(buf + pos, size - pos,
-				 " cost.wait=%llu cost.indebt=%llu cost.indelay=%llu",
-				 iocg->last_stat.wait_us,
-				 iocg->last_stat.indebt_us,
-				 iocg->last_stat.indelay_us);
-
-	return pos;
+		seq_printf(s, " cost.wait=%llu cost.indebt=%llu cost.indelay=%llu",
+			iocg->last_stat.wait_us,
+			iocg->last_stat.indebt_us,
+			iocg->last_stat.indelay_us);
+	return true;
 }
 
 static u64 ioc_weight_prfill(struct seq_file *sf, struct blkg_policy_data *pd,

block/blk-iolatency.c

@@ -886,8 +886,7 @@ static int iolatency_print_limit(struct seq_file *sf, void *v)
 	return 0;
 }
 
-static size_t iolatency_ssd_stat(struct iolatency_grp *iolat, char *buf,
-				 size_t size)
+static bool iolatency_ssd_stat(struct iolatency_grp *iolat, struct seq_file *s)
 {
 	struct latency_stat stat;
 	int cpu;
@@ -902,39 +901,40 @@ static size_t iolatency_ssd_stat(struct iolatency_grp *iolat, char *buf,
 	preempt_enable();
 
 	if (iolat->rq_depth.max_depth == UINT_MAX)
-		return scnprintf(buf, size, " missed=%llu total=%llu depth=max",
-				 (unsigned long long)stat.ps.missed,
-				 (unsigned long long)stat.ps.total);
-	return scnprintf(buf, size, " missed=%llu total=%llu depth=%u",
-			 (unsigned long long)stat.ps.missed,
-			 (unsigned long long)stat.ps.total,
-			 iolat->rq_depth.max_depth);
+		seq_printf(s, " missed=%llu total=%llu depth=max",
+			(unsigned long long)stat.ps.missed,
+			(unsigned long long)stat.ps.total);
+	else
+		seq_printf(s, " missed=%llu total=%llu depth=%u",
+			(unsigned long long)stat.ps.missed,
+			(unsigned long long)stat.ps.total,
+			iolat->rq_depth.max_depth);
+	return true;
 }
 
-static size_t iolatency_pd_stat(struct blkg_policy_data *pd, char *buf,
-				size_t size)
+static bool iolatency_pd_stat(struct blkg_policy_data *pd, struct seq_file *s)
 {
 	struct iolatency_grp *iolat = pd_to_lat(pd);
 	unsigned long long avg_lat;
 	unsigned long long cur_win;
 
 	if (!blkcg_debug_stats)
-		return 0;
+		return false;
 
 	if (iolat->ssd)
-		return iolatency_ssd_stat(iolat, buf, size);
+		return iolatency_ssd_stat(iolat, s);
 
 	avg_lat = div64_u64(iolat->lat_avg, NSEC_PER_USEC);
 	cur_win = div64_u64(iolat->cur_win_nsec, NSEC_PER_MSEC);
 	if (iolat->rq_depth.max_depth == UINT_MAX)
-		return scnprintf(buf, size, " depth=max avg_lat=%llu win=%llu",
-				 avg_lat, cur_win);
-
-	return scnprintf(buf, size, " depth=%u avg_lat=%llu win=%llu",
-			 iolat->rq_depth.max_depth, avg_lat, cur_win);
+		seq_printf(s, " depth=max avg_lat=%llu win=%llu",
+			avg_lat, cur_win);
+	else
+		seq_printf(s, " depth=%u avg_lat=%llu win=%llu",
+			iolat->rq_depth.max_depth, avg_lat, cur_win);
+	return true;
 }
 
-
 static struct blkg_policy_data *iolatency_pd_alloc(gfp_t gfp,
 						   struct request_queue *q,
 						   struct blkcg *blkcg)

block/mq-deadline-cgroup.c

@@ -52,7 +52,7 @@ struct dd_blkcg *dd_blkcg_from_bio(struct bio *bio)
 	return dd_blkcg_from_pd(pd);
 }
 
-static size_t dd_pd_stat(struct blkg_policy_data *pd, char *buf, size_t size)
+static bool dd_pd_stat(struct blkg_policy_data *pd, struct seq_file *s)
 {
 	static const char *const prio_class_name[] = {
 		[IOPRIO_CLASS_NONE]	= "NONE",
@@ -61,12 +61,10 @@ static size_t dd_pd_stat(struct blkg_policy_data *pd, char *buf, size_t size)
 		[IOPRIO_CLASS_IDLE]	= "IDLE",
 	};
 	struct dd_blkcg *blkcg = dd_blkcg_from_pd(pd);
-	int res = 0;
 	u8 prio;
 
 	for (prio = 0; prio < ARRAY_SIZE(blkcg->stats->stats); prio++)
-		res += scnprintf(buf + res, size - res,
-			" [%s] dispatched=%u inserted=%u merged=%u",
+		seq_printf(s, " [%s] dispatched=%u inserted=%u merged=%u",
 			prio_class_name[prio],
 			ddcg_sum(blkcg, dispatched, prio) +
 			ddcg_sum(blkcg, merged, prio) -
@@ -75,7 +73,7 @@ static size_t dd_pd_stat(struct blkg_policy_data *pd, char *buf, size_t size)
 			ddcg_sum(blkcg, completed, prio),
 			ddcg_sum(blkcg, merged, prio));
 
-	return res;
+	return true;
 }
 
 static struct blkg_policy_data *dd_pd_alloc(gfp_t gfp, struct request_queue *q,

include/linux/blk-cgroup.h

@@ -152,8 +152,8 @@ typedef void (blkcg_pol_online_pd_fn)(struct blkg_policy_data *pd);
 typedef void (blkcg_pol_offline_pd_fn)(struct blkg_policy_data *pd);
 typedef void (blkcg_pol_free_pd_fn)(struct blkg_policy_data *pd);
 typedef void (blkcg_pol_reset_pd_stats_fn)(struct blkg_policy_data *pd);
-typedef size_t (blkcg_pol_stat_pd_fn)(struct blkg_policy_data *pd, char *buf,
-				      size_t size);
+typedef bool (blkcg_pol_stat_pd_fn)(struct blkg_policy_data *pd,
+				struct seq_file *s);
 
 struct blkcg_policy {
 	int				plid;