linux-kernel - Re: [PATCH 2/2] scsi: fnic: Remove unnecessary spinlock locking and unlocking

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Message-ID: <80809232-9490-4a0d-8159-af53228b612b@stanley.mountain>
Date: Wed, 26 Feb 2025 10:32:04 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Karan Tilak Kumar <kartilak@...co.com>
Cc: sebaddel@...co.com, arulponn@...co.com, djhawar@...co.com,
	gcboffa@...co.com, mkai2@...co.com, satishkh@...co.com,
	aeasi@...co.com, jejb@...ux.ibm.com, martin.petersen@...cle.com,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] scsi: fnic: Remove unnecessary spinlock locking and
 unlocking

On Tue, Feb 25, 2025 at 01:51:46PM -0800, Karan Tilak Kumar wrote:
> diff --git a/drivers/scsi/fnic/fdls_disc.c b/drivers/scsi/fnic/fdls_disc.c
> index 8843d9486dbb..6530298733f0 100644
> --- a/drivers/scsi/fnic/fdls_disc.c
> +++ b/drivers/scsi/fnic/fdls_disc.c
> @@ -311,36 +311,30 @@ void fdls_schedule_oxid_free_retry_work(struct work_struct *work)
>  	unsigned long flags;
>  	int idx;
>  
> -	spin_lock_irqsave(&fnic->fnic_lock, flags);
> -
>  	for_each_set_bit(idx, oxid_pool->pending_schedule_free, FNIC_OXID_POOL_SZ) {
>  
>  		FNIC_FCS_DBG(KERN_INFO, fnic->host, fnic->fnic_num,
>  			"Schedule oxid free. oxid idx: %d\n", idx);
>  
> -		spin_unlock_irqrestore(&fnic->fnic_lock, flags);
>  		reclaim_entry = kzalloc(sizeof(*reclaim_entry), GFP_KERNEL);
> -		spin_lock_irqsave(&fnic->fnic_lock, flags);
> -
>  		if (!reclaim_entry) {
>  			schedule_delayed_work(&oxid_pool->schedule_oxid_free_retry,
>  				msecs_to_jiffies(SCHEDULE_OXID_FREE_RETRY_TIME));
> -			spin_unlock_irqrestore(&fnic->fnic_lock, flags);
>  			return;
>  		}
>  
>  		if (test_and_clear_bit(idx, oxid_pool->pending_schedule_free)) {

We discussed this earlier and I really should have brought it up then,
but what is this check about?  We "know" (scare quotes) that it is true
because we're inside a for_each_set_bit() loop.  I had assumed it was to
test for race conditions so that's why I put it under the lock.  If the
locking doesn't matter then we could just do a clear_bit() without doing
a second test.

regards,
dan carpenter

>  			reclaim_entry->oxid_idx = idx;
>  			reclaim_entry->expires = round_jiffies(jiffies + delay_j);
> +			spin_lock_irqsave(&fnic->fnic_lock, flags);
>  			list_add_tail(&reclaim_entry->links, &oxid_pool->oxid_reclaim_list);
> +			spin_unlock_irqrestore(&fnic->fnic_lock, flags);
>  			schedule_delayed_work(&oxid_pool->oxid_reclaim_work, delay_j);
>  		} else {
>  			/* unlikely scenario, free the allocated memory and continue */
>  			kfree(reclaim_entry);
>  		}
>  	}

> -
> -	spin_unlock_irqrestore(&fnic->fnic_lock, flags);
>  }
>  
>  static bool fdls_is_oxid_fabric_req(uint16_t oxid)
> -- 
> 2.47.1