linux-kernel - Re: [PATCH 3/4] scsi: pm8001: Use non-atomic bitmap ops for tag alloc + free

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Message-ID: <303bbfad-edde-1197-679e-4a09175fb1f3@suse.de>
Date:   Mon, 20 Jun 2022 08:00:38 +0200
From:   Hannes Reinecke <hare@...e.de>
To:     John Garry <john.garry@...wei.com>, jinpu.wang@...ud.ionos.com,
        jejb@...ux.ibm.com, martin.petersen@...cle.com
Cc:     linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        damien.lemoal@...nsource.wdc.com, Ajish.Koshy@...rochip.com
Subject: Re: [PATCH 3/4] scsi: pm8001: Use non-atomic bitmap ops for tag alloc
 + free

On 6/10/22 18:46, John Garry wrote:
> In pm8001_tag_alloc() we don't require atomic set_bit() as we are already
> in atomic context. In pm8001_tag_free() we should use the same host
> spinlock to protect clearing the tag (and then don't require the atomic
> clear_bit()).
> 
> Signed-off-by: John Garry <john.garry@...wei.com>
> ---
>   drivers/scsi/pm8001/pm8001_sas.c | 10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/scsi/pm8001/pm8001_sas.c b/drivers/scsi/pm8001/pm8001_sas.c
> index 3a863d776724..8e3f2f9ddaac 100644
> --- a/drivers/scsi/pm8001/pm8001_sas.c
> +++ b/drivers/scsi/pm8001/pm8001_sas.c
> @@ -66,7 +66,11 @@ static int pm8001_find_tag(struct sas_task *task, u32 *tag)
>   void pm8001_tag_free(struct pm8001_hba_info *pm8001_ha, u32 tag)
>   {
>   	void *bitmap = pm8001_ha->tags;
> -	clear_bit(tag, bitmap);
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&pm8001_ha->bitmap_lock, flags);
> +	__clear_bit(tag, bitmap);
> +	spin_unlock_irqrestore(&pm8001_ha->bitmap_lock, flags);
>   }
>   
This spin lock is pretty much pointless; clear_bit() is always atomic.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@...e.de                              +49 911 74053 688
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