blk-iocost: don't release 'ioc->lock' while updating params

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@huawei.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20221012094035.390056-3-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 0803647..6d36a4b 100644 (file)
--- 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);