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

[Hannes Reinecke <hare@suse.de>]

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
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