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From:   Tejun Heo <tj@kernel.org>
To:     axboe@kernel.dk
Cc:     linux-block@vger.kernel.org, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org, kernel-team@fb.com, newella@fb.com,
        Tejun Heo <tj@kernel.org>
Subject: [PATCH 03/27] blk-iocost: use local[64]_t for percpu stat
Date:   Tue,  1 Sep 2020 14:52:33 -0400
Message-Id: <20200901185257.645114-4-tj@kernel.org>
In-Reply-To: <20200901185257.645114-1-tj@kernel.org>
References: <20200901185257.645114-1-tj@kernel.org>
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

blk-iocost has been reading percpu stat counters from remote cpus which on
some archs can lead to torn reads in really rare occassions. Use local[64]_t
for those counters.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
 block/blk-iocost.c | 37 +++++++++++++++++++++++++++----------
 1 file changed, 27 insertions(+), 10 deletions(-)

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index d37b55db2409..e2266e7692b4 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -179,6 +179,8 @@
 #include <linux/parser.h>
 #include <linux/sched/signal.h>
 #include <linux/blk-cgroup.h>
+#include <asm/local.h>
+#include <asm/local64.h>
 #include "blk-rq-qos.h"
 #include "blk-stat.h"
 #include "blk-wbt.h"
@@ -373,8 +375,8 @@ struct ioc_params {
 };
 
 struct ioc_missed {
-	u32				nr_met;
-	u32				nr_missed;
+	local_t				nr_met;
+	local_t				nr_missed;
 	u32				last_met;
 	u32				last_missed;
 };
@@ -382,7 +384,7 @@ struct ioc_missed {
 struct ioc_pcpu_stat {
 	struct ioc_missed		missed[2];
 
-	u64				rq_wait_ns;
+	local64_t			rq_wait_ns;
 	u64				last_rq_wait_ns;
 };
 
@@ -1278,8 +1280,8 @@ static void ioc_lat_stat(struct ioc *ioc, u32 *missed_ppm_ar, u32 *rq_wait_pct_p
 		u64 this_rq_wait_ns;
 
 		for (rw = READ; rw <= WRITE; rw++) {
-			u32 this_met = READ_ONCE(stat->missed[rw].nr_met);
-			u32 this_missed = READ_ONCE(stat->missed[rw].nr_missed);
+			u32 this_met = local_read(&stat->missed[rw].nr_met);
+			u32 this_missed = local_read(&stat->missed[rw].nr_missed);
 
 			nr_met[rw] += this_met - stat->missed[rw].last_met;
 			nr_missed[rw] += this_missed - stat->missed[rw].last_missed;
@@ -1287,7 +1289,7 @@ static void ioc_lat_stat(struct ioc *ioc, u32 *missed_ppm_ar, u32 *rq_wait_pct_p
 			stat->missed[rw].last_missed = this_missed;
 		}
 
-		this_rq_wait_ns = READ_ONCE(stat->rq_wait_ns);
+		this_rq_wait_ns = local64_read(&stat->rq_wait_ns);
 		rq_wait_ns += this_rq_wait_ns - stat->last_rq_wait_ns;
 		stat->last_rq_wait_ns = this_rq_wait_ns;
 	}
@@ -1908,6 +1910,7 @@ static void ioc_rqos_done_bio(struct rq_qos *rqos, struct bio *bio)
 static void ioc_rqos_done(struct rq_qos *rqos, struct request *rq)
 {
 	struct ioc *ioc = rqos_to_ioc(rqos);
+	struct ioc_pcpu_stat *ccs;
 	u64 on_q_ns, rq_wait_ns, size_nsec;
 	int pidx, rw;
 
@@ -1931,13 +1934,17 @@ static void ioc_rqos_done(struct rq_qos *rqos, struct request *rq)
 	rq_wait_ns = rq->start_time_ns - rq->alloc_time_ns;
 	size_nsec = div64_u64(calc_size_vtime_cost(rq, ioc), VTIME_PER_NSEC);
 
+	ccs = get_cpu_ptr(ioc->pcpu_stat);
+
 	if (on_q_ns <= size_nsec ||
 	    on_q_ns - size_nsec <= ioc->params.qos[pidx] * NSEC_PER_USEC)
-		this_cpu_inc(ioc->pcpu_stat->missed[rw].nr_met);
+		local_inc(&ccs->missed[rw].nr_met);
 	else
-		this_cpu_inc(ioc->pcpu_stat->missed[rw].nr_missed);
+		local_inc(&ccs->missed[rw].nr_missed);
+
+	local64_add(rq_wait_ns, &ccs->rq_wait_ns);
 
-	this_cpu_add(ioc->pcpu_stat->rq_wait_ns, rq_wait_ns);
+	put_cpu_ptr(ccs);
 }
 
 static void ioc_rqos_queue_depth_changed(struct rq_qos *rqos)
@@ -1977,7 +1984,7 @@ static int blk_iocost_init(struct request_queue *q)
 {
 	struct ioc *ioc;
 	struct rq_qos *rqos;
-	int ret;
+	int i, cpu, ret;
 
 	ioc = kzalloc(sizeof(*ioc), GFP_KERNEL);
 	if (!ioc)
@@ -1989,6 +1996,16 @@ static int blk_iocost_init(struct request_queue *q)
 		return -ENOMEM;
 	}
 
+	for_each_possible_cpu(cpu) {
+		struct ioc_pcpu_stat *ccs = per_cpu_ptr(ioc->pcpu_stat, cpu);
+
+		for (i = 0; i < ARRAY_SIZE(ccs->missed); i++) {
+			local_set(&ccs->missed[i].nr_met, 0);
+			local_set(&ccs->missed[i].nr_missed, 0);
+		}
+		local64_set(&ccs->rq_wait_ns, 0);
+	}
+
 	rqos = &ioc->rqos;
 	rqos->id = RQ_QOS_COST;
 	rqos->ops = &ioc_rqos_ops;
-- 
2.26.2