linux-kernel - [PATCH -next 4/4] blk-iocost: guarantee the exit order of iocg

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Message-Id: <20221217030527.1250083-5-yukuai1@huaweicloud.com>
Date:   Sat, 17 Dec 2022 11:05:27 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     tj@...nel.org, hch@...radead.org, josef@...icpanda.com,
        axboe@...nel.dk
Cc:     cgroups@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, yukuai3@...wei.com,
        yukuai1@...weicloud.com, yi.zhang@...wei.com
Subject: [PATCH -next 4/4] blk-iocost: guarantee the exit order of iocg

From: Yu Kuai <yukuai3@...wei.com>

pd_offline_fn() is ensured to be called in order(parent after child),
while pd_free_fn() is not. Furthermore, rq_qos_exit() can also be called
before pd_free_fn(). For conclusion, doing cleanups in ioc_pd_free() is
not safe, which can cause many problems. By the way, iocost is the only
policy to do cleanups in pd_free_fn().

Since previous patches guarantee that ioc_pd_offline() will dispatch
throttled bio and prevent new io to be throttled. It's safe to move
cleanup operations for iocg from ioc_pd_free() to ioc_pd_offline().

Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
 block/blk-iocost.c | 26 ++++++++++----------------
 1 file changed, 10 insertions(+), 16 deletions(-)

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index b63ecfdd815c..d634ea73f991 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -3011,21 +3011,6 @@ static void ioc_pd_offline(struct blkg_policy_data *pd)
 
 		iocg_lock(iocg, true, &flags);
 		iocg->online = false;
-		iocg_unlock(iocg, true, &flags);
-
-		hrtimer_cancel(&iocg->waitq_timer);
-		__wake_up(&iocg->waitq, TASK_NORMAL, 0, &ctx);
-	}
-}
-
-static void ioc_pd_free(struct blkg_policy_data *pd)
-{
-	struct ioc_gq *iocg = pd_to_iocg(pd);
-	struct ioc *ioc = iocg->ioc;
-	unsigned long flags;
-
-	if (ioc) {
-		spin_lock_irqsave(&ioc->lock, flags);
 
 		if (!list_empty(&iocg->active_list)) {
 			struct ioc_now now;
@@ -3038,8 +3023,17 @@ static void ioc_pd_free(struct blkg_policy_data *pd)
 		WARN_ON_ONCE(!list_empty(&iocg->walk_list));
 		WARN_ON_ONCE(!list_empty(&iocg->surplus_list));
 
-		spin_unlock_irqrestore(&ioc->lock, flags);
+		iocg_unlock(iocg, true, &flags);
+
+		hrtimer_cancel(&iocg->waitq_timer);
+		__wake_up(&iocg->waitq, TASK_NORMAL, 0, &ctx);
 	}
+}
+
+static void ioc_pd_free(struct blkg_policy_data *pd)
+{
+	struct ioc_gq *iocg = pd_to_iocg(pd);
+
 	free_percpu(iocg->pcpu_stat);
 	kfree(iocg);
 }
-- 
2.31.1