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    SubjectRe: [PATCH v2 4/5] blk-iocost: fix sleeping in atomic context warnning
    On Fri, Nov 04, 2022 at 10:39:37AM +0800, Yu Kuai wrote:
    > From: Yu Kuai <yukuai3@huawei.com>
    >
    > match_u64() is called inside ioc->lock, which causes smatch static
    > checker warnings:
    >
    > block/blk-iocost.c:3211 ioc_qos_write() warn: sleeping in atomic context
    > block/blk-iocost.c:3240 ioc_qos_write() warn: sleeping in atomic context
    > block/blk-iocost.c:3407 ioc_cost_model_write() warn: sleeping in atomic
    > context
    >
    > Fix the problem by introducing a mutex and using it while prasing input
    > params.

    It bothers me that parsing an u64 string requires a GFP_KERNEL memory
    allocation.

    > @@ -2801,9 +2806,11 @@ static void ioc_rqos_queue_depth_changed(struct rq_qos *rqos)
    > {
    > struct ioc *ioc = rqos_to_ioc(rqos);
    >
    > + mutex_lock(&ioc->params_mutex);
    > spin_lock_irq(&ioc->lock);
    > ioc_refresh_params(ioc, false);
    > spin_unlock_irq(&ioc->lock);
    > + mutex_unlock(&ioc->params_mutex);
    > }

    Aren't the params still protected by ioc->lock? Why do we need to grab both?

    Any chance I can persuade you into updating match_NUMBER() helpers to not
    use match_strdup()? They can easily disable irq/preemption and use percpu
    buffers and we won't need most of this patchset.

    Thanks.

    --
    tejun

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