linux-kernel - [PATCH -next 2/5] blk-iocost: don't release 'ioc->lock' while updating params

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Date:   Tue, 11 Oct 2022 16:35:44 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     tj@...nel.org, axboe@...nel.dk
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        yukuai3@...wei.com, yukuai1@...weicloud.com, yi.zhang@...wei.com
Subject: [PATCH -next 2/5] blk-iocost: don't release 'ioc->lock' while updating params

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

ioc_qos_write() and ioc_cost_model_write() are the same:

1) hold lock to read 'ioc->params' to local variable;
2) update params to local variable without lock;
3) hold lock to write local variable to 'ioc->params';

In theroy, if user updates params concurrenty, the params might be lost:

t1: update params a		t2: update params b
spin_lock_irq(&ioc->lock);
memcpy(qos, ioc->params.qos, sizeof(qos))
spin_unlock_irq(&ioc->lock);

qos[a] = xxx;

				spin_lock_irq(&ioc->lock);
				memcpy(qos, ioc->params.qos, sizeof(qos))
				spin_unlock_irq(&ioc->lock);

				qos[b] = xxx;

spin_lock_irq(&ioc->lock);
memcpy(ioc->params.qos, qos, sizeof(qos));
ioc_refresh_params(ioc, true);
spin_unlock_irq(&ioc->lock);

				spin_lock_irq(&ioc->lock);
				// updates of a will be lost
				memcpy(ioc->params.qos, qos, sizeof(qos));
				ioc_refresh_params(ioc, true);
				spin_unlock_irq(&ioc->lock);

Althrough this is not common case, the problem can by fixed easily by
holding the lock through the read, update, write process.

Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
 block/blk-iocost.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 08036476e6fa..6d36a4bd4382 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -3191,7 +3191,6 @@ static ssize_t ioc_qos_write(struct kernfs_open_file *of, char *input,
 	memcpy(qos, ioc->params.qos, sizeof(qos));
 	enable = ioc->enabled;
 	user = ioc->user_qos_params;
-	spin_unlock_irq(&ioc->lock);
 
 	while ((p = strsep(&input, " \t\n"))) {
 		substring_t args[MAX_OPT_ARGS];
@@ -3258,8 +3257,6 @@ static ssize_t ioc_qos_write(struct kernfs_open_file *of, char *input,
 	if (qos[QOS_MIN] > qos[QOS_MAX])
 		goto einval;
 
-	spin_lock_irq(&ioc->lock);
-
 	if (enable) {
 		blk_stat_enable_accounting(disk->queue);
 		blk_queue_flag_set(QUEUE_FLAG_RQ_ALLOC_TIME, disk->queue);
@@ -3284,6 +3281,7 @@ static ssize_t ioc_qos_write(struct kernfs_open_file *of, char *input,
 	blkdev_put_no_open(bdev);
 	return nbytes;
 einval:
+	spin_unlock_irq(&ioc->lock);
 	ret = -EINVAL;
 err:
 	blkdev_put_no_open(bdev);
@@ -3359,7 +3357,6 @@ static ssize_t ioc_cost_model_write(struct kernfs_open_file *of, char *input,
 	spin_lock_irq(&ioc->lock);
 	memcpy(u, ioc->params.i_lcoefs, sizeof(u));
 	user = ioc->user_cost_model;
-	spin_unlock_irq(&ioc->lock);
 
 	while ((p = strsep(&input, " \t\n"))) {
 		substring_t args[MAX_OPT_ARGS];
@@ -3396,7 +3393,6 @@ static ssize_t ioc_cost_model_write(struct kernfs_open_file *of, char *input,
 		user = true;
 	}
 
-	spin_lock_irq(&ioc->lock);
 	if (user) {
 		memcpy(ioc->params.i_lcoefs, u, sizeof(u));
 		ioc->user_cost_model = true;
@@ -3410,6 +3406,7 @@ static ssize_t ioc_cost_model_write(struct kernfs_open_file *of, char *input,
 	return nbytes;
 
 einval:
+	spin_unlock_irq(&ioc->lock);
 	ret = -EINVAL;
 err:
 	blkdev_put_no_open(bdev);
-- 
2.31.1