linux-kernel - [PATCH RFC v2 7/7] blk-iocost: support to build iocost as kernel module

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Date: Tue, 18 Jun 2024 11:17:51 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: axboe@...nel.dk,
	tj@...nel.org,
	gregkh@...uxfoundation.org,
	bvanassche@....org,
	hch@...radead.org,
	josef@...icpanda.com,
	lizefan.x@...edance.com,
	hannes@...xchg.org
Cc: linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org,
	yukuai3@...wei.com,
	yukuai1@...weicloud.com,
	yi.zhang@...wei.com,
	yangerkun@...wei.com
Subject: [PATCH RFC v2 7/7] blk-iocost: support to build iocost as kernel module

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

The motivation is that iocost is not used widely in our production, and
some customers don't want to increase kernel size to enable iocost that
they will never use, and it'll be painful to maintain a new downstream
kernel version. Hence it'll be beneficially to build iocost as kernel
module:

- Kernel Size and Resource Usage, modules are loaded only when their
specific functionality is required.

- Flexibility and Maintainability, allows for dynamic loading and unloading
of modules at runtime without the need to recompile and restart the kernel,
for example we can just replace blk-iocost.ko to fix iocost CVE in our
production environment.

Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
 block/Kconfig             |  2 +-
 block/blk-iocost.c        | 14 +++++++++++++-
 include/linux/blk_types.h |  2 +-
 3 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/block/Kconfig b/block/Kconfig
index dc12af58dbae..b94b93158e57 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -156,7 +156,7 @@ config BLK_CGROUP_FC_APPID
 	  application specific identification into the FC frame.
 
 config BLK_CGROUP_IOCOST
-	bool "Enable support for cost model based cgroup IO controller"
+	tristate "Enable support for cost model based cgroup IO controller"
 	depends on BLK_CGROUP
 	select BLK_RQ_ALLOC_TIME
 	help
diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 9765c988113f..33ab6e436af2 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -2850,6 +2850,7 @@ static void ioc_rqos_queue_depth_changed(struct rq_qos *rqos)
 
 static void __ioc_exit(struct ioc *ioc)
 {
+	module_put(THIS_MODULE);
 	blkcg_deactivate_policy(ioc->rqos.disk, &blkcg_policy_iocost);
 
 	spin_lock_irq(&ioc->lock);
@@ -2882,13 +2883,19 @@ static int blk_iocost_init(struct gendisk *disk)
 	struct ioc *ioc;
 	int i, cpu, ret;
 
+	if (!try_module_get(THIS_MODULE))
+		return -ENODEV;
+
 	ioc = kzalloc(sizeof(*ioc), GFP_KERNEL);
-	if (!ioc)
+	if (!ioc) {
+		module_put(THIS_MODULE);
 		return -ENOMEM;
+	}
 
 	ioc->pcpu_stat = alloc_percpu(struct ioc_pcpu_stat);
 	if (!ioc->pcpu_stat) {
 		kfree(ioc);
+		module_put(THIS_MODULE);
 		return -ENOMEM;
 	}
 
@@ -2938,6 +2945,7 @@ static int blk_iocost_init(struct gendisk *disk)
 	rq_qos_del(&ioc->rqos);
 err_free_ioc:
 	free_percpu(ioc->pcpu_stat);
+	module_put(THIS_MODULE);
 	kfree(ioc);
 	return ret;
 }
@@ -3616,3 +3624,7 @@ static void __exit ioc_exit(void)
 
 module_init(ioc_init);
 module_exit(ioc_exit);
+
+MODULE_AUTHOR("Tejun Heo");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Cost model based cgroup IO controller");
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 781c4500491b..8da12ebc7777 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -234,7 +234,7 @@ struct bio {
 	 */
 	struct blkcg_gq		*bi_blkg;
 	struct bio_issue	bi_issue;
-#ifdef CONFIG_BLK_CGROUP_IOCOST
+#if IS_ENABLED(CONFIG_BLK_CGROUP_IOCOST)
 	u64			bi_iocost_cost;
 #endif
 #endif
-- 
2.39.2