Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <303bbfad-edde-1197-679e-4a09175fb1f3@suse.de>
Date:   Mon, 20 Jun 2022 08:00:38 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.4.0
Subject: Re: [PATCH 3/4] scsi: pm8001: Use non-atomic bitmap ops for tag alloc
 + free
Content-Language: en-US
To:     John Garry <john.garry@huawei.com>, jinpu.wang@cloud.ionos.com,
        jejb@linux.ibm.com, martin.petersen@oracle.com
Cc:     linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
        damien.lemoal@opensource.wdc.com, Ajish.Koshy@microchip.com
References: <1654879602-33497-1-git-send-email-john.garry@huawei.com>
 <1654879602-33497-4-git-send-email-john.garry@huawei.com>
From:   Hannes Reinecke <hare@suse.de>
In-Reply-To: <1654879602-33497-4-git-send-email-john.garry@huawei.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk

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@huawei.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@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Ivo Totev, Andrew
Myers, Andrew McDonald, Martje Boudien Moerman