Re: [PATCH v2 4/5] blk-iocost: fix sleeping in atomic context warnning

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Hi,

在 2022/11/15 6:07, Tejun Heo 写道:
On Fri, Nov 04, 2022 at 10:39:37AM +0800, Yu Kuai wrote:
From: Yu Kuai <yukuai3@xxxxxxxxxx>

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?

Yes, the params is updated inside ioc->lock, but they can be read
without the lock before updating them, which is protected by mutex
instead.


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.

Do you mean preallocated percpu buffer? Is there any example I can
learn? Anyway, replace match_strdup() to avoid memory allocation sounds
good.

Thanks,
Kuai

Thanks.





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