linux-kernel - Re: [PATCH v2] blk_iocost: remove some duplicate irq disable/enables

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Message-ID: <0a8fe25b-9b72-496d-b1fc-e8f773151e0a@redhat.com>
Date: Wed, 2 Oct 2024 13:49:48 -0400
From: Waiman Long <longman@...hat.com>
To: Dan Carpenter <dan.carpenter@...aro.org>, Yu Kuai <yukuai3@...wei.com>
Cc: Tejun Heo <tj@...nel.org>, Josef Bacik <josef@...icpanda.com>,
 Jens Axboe <axboe@...nel.dk>, cgroups@...r.kernel.org,
 linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 kernel-janitors@...r.kernel.org, Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2] blk_iocost: remove some duplicate irq disable/enables

On 10/2/24 06:47, Dan Carpenter wrote:
> These are called from blkcg_print_blkgs() which already disables IRQs so
> disabling it again is wrong.  It means that IRQs will be enabled slightly
> earlier than intended, however, so far as I can see, this bug is harmless.
>
> Fixes: 35198e323001 ("blk-iocost: read params inside lock in sysfs apis")
> Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
> Reviewed-by: Christoph Hellwig <hch@....de>
> ---
> v2: Fix typo in the subject
>
>   block/blk-iocost.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/block/blk-iocost.c b/block/blk-iocost.c
> index 9dc9323f84ac..384aa15e8260 100644
> --- a/block/blk-iocost.c
> +++ b/block/blk-iocost.c
> @@ -3166,7 +3166,7 @@ static u64 ioc_qos_prfill(struct seq_file *sf, struct blkg_policy_data *pd,
>   	if (!dname)
>   		return 0;
>   
> -	spin_lock_irq(&ioc->lock);
> +	spin_lock(&ioc->lock);
>   	seq_printf(sf, "%s enable=%d ctrl=%s rpct=%u.%02u rlat=%u wpct=%u.%02u wlat=%u min=%u.%02u max=%u.%02u\n",
>   		   dname, ioc->enabled, ioc->user_qos_params ? "user" : "auto",
>   		   ioc->params.qos[QOS_RPPM] / 10000,
> @@ -3179,7 +3179,7 @@ static u64 ioc_qos_prfill(struct seq_file *sf, struct blkg_policy_data *pd,
>   		   ioc->params.qos[QOS_MIN] % 10000 / 100,
>   		   ioc->params.qos[QOS_MAX] / 10000,
>   		   ioc->params.qos[QOS_MAX] % 10000 / 100);
> -	spin_unlock_irq(&ioc->lock);
> +	spin_unlock(&ioc->lock);
>   	return 0;
>   }
>   
> @@ -3366,14 +3366,14 @@ static u64 ioc_cost_model_prfill(struct seq_file *sf,
>   	if (!dname)
>   		return 0;
>   
> -	spin_lock_irq(&ioc->lock);
> +	spin_lock(&ioc->lock);
>   	seq_printf(sf, "%s ctrl=%s model=linear "
>   		   "rbps=%llu rseqiops=%llu rrandiops=%llu "
>   		   "wbps=%llu wseqiops=%llu wrandiops=%llu\n",
>   		   dname, ioc->user_cost_model ? "user" : "auto",
>   		   u[I_LCOEF_RBPS], u[I_LCOEF_RSEQIOPS], u[I_LCOEF_RRANDIOPS],
>   		   u[I_LCOEF_WBPS], u[I_LCOEF_WSEQIOPS], u[I_LCOEF_WRANDIOPS]);
> -	spin_unlock_irq(&ioc->lock);
> +	spin_unlock(&ioc->lock);
>   	return 0;
>   }
>   

I would suggest adding a "lockdep_assert_irqs_disabled()" call before 
spin_lock() to confirm that irq is indeed disabled just in case the 
callers are changed in the future.

Cheers,
Longman