linux-kernel - Re: [PATCH] scsi: megaraid_sas: use spin

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Date:   Thu, 22 Oct 2020 13:25:00 +1100 (AEDT)
From:   Finn Thain <fthain@...egraphics.com.au>
To:     Xianting Tian <tian.xianting@....com>
cc:     kashyap.desai@...adcom.com, sumit.saxena@...adcom.com,
        shivasharan.srikanteshwara@...adcom.com, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, megaraidlinux.pdl@...adcom.com,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi: megaraid_sas: use spin_lock() in hard IRQ

On Wed, 21 Oct 2020, Xianting Tian wrote:

> Since we already in hard IRQ context when running megasas_isr(),

On m68k, hard irq context does not mean interrupts are disabled. Are there 
no other architectures in that category?

> so use spin_lock() is enough, which is faster than spin_lock_irqsave().
> 

Is that measurable?

> Signed-off-by: Xianting Tian <tian.xianting@....com>
> ---
>  drivers/scsi/megaraid/megaraid_sas_base.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/scsi/megaraid/megaraid_sas_base.c b/drivers/scsi/megaraid/megaraid_sas_base.c
> index 2b7e7b5f3..bd186254d 100644
> --- a/drivers/scsi/megaraid/megaraid_sas_base.c
> +++ b/drivers/scsi/megaraid/megaraid_sas_base.c
> @@ -3977,15 +3977,14 @@ static irqreturn_t megasas_isr(int irq, void *devp)
>  {
>  	struct megasas_irq_context *irq_context = devp;
>  	struct megasas_instance *instance = irq_context->instance;
> -	unsigned long flags;
>  	irqreturn_t rc;
>  
>  	if (atomic_read(&instance->fw_reset_no_pci_access))
>  		return IRQ_HANDLED;
>  
> -	spin_lock_irqsave(&instance->hba_lock, flags);
> +	spin_lock(&instance->hba_lock);
>  	rc = megasas_deplete_reply_queue(instance, DID_OK);
> -	spin_unlock_irqrestore(&instance->hba_lock, flags);
> +	spin_unlock(&instance->hba_lock);
>  
>  	return rc;
>  }
>