linux-kernel - Re: [PATCH 1/2] [SCSI] pm8001: Fix bogus interrupt state flag issue.

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Date:	Mon, 27 Feb 2012 10:27:50 +0530
From:	santosh prasad nayak <santoshprasadnayak@...il.com>
To:	Dan Carpenter <dan.carpenter@...cle.com>
Cc:	jack_wang@...sh.com, lindar_liu@...sh.com,
	JBottomley@...allels.com, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 1/2] [SCSI] pm8001: Fix bogus interrupt state flag issue.

 In 'mpi_sata_completion'
 the first call for 'spin_unlock_irqrestore()' is with flags=0,
 which is as good as 'spin_unlock_irq()' ( unconditional interrupt
 enabling). If intention of the developer is to enable the interrupt during
execution of ' mpi_sata_completion' , then the code changes in the patch
looks ok.

If interrupt should not be enabled during execution of
'mpi_sata_completion' then
we can use simple  spin_lock and spin_unlock.


regards
santosh


On Sun, Feb 26, 2012 at 8:37 PM, Dan Carpenter <dan.carpenter@...cle.com> wrote:
> On Sun, Feb 26, 2012 at 07:03:30PM +0530, santosh nayak wrote:
>> From: Santosh Nayak <santoshprasadnayak@...il.com>
>>
>> Static checker is giving following warning:
>> " error: calling 'spin_unlock_irqrestore()' with bogus flags"
>>
>> The code flow is as shown below:
>> process_oq() --> process_one_iomb --> mpi_sata_completion
>>
>> In 'mpi_sata_completion'
>> the first call for 'spin_unlock_irqrestore()' is with flags=0,
>> which is as good as 'spin_unlock_irq()' ( unconditional interrupt
>> enabling).
>>
>> So for better performance 'spin_unlock_irqrestore()' can be replaced
>> with 'spin_unlock_irq()' and 'spin_lock_irqsave()' can be replaced by
>> 'spin_lock_irq()'.
>>
>
> process_oq() is called from the interrupt handler pm8001_chip_isr()
> with interrupts disabled.
>
> drivers/scsi/pm8001/pm8001_hwi.c
>  4301          spin_lock_irqsave(&pm8001_ha->lock, flags);
>  4302          pm8001_chip_interrupt_disable(pm8001_ha);
>  4303          process_oq(pm8001_ha);
>  4304          pm8001_chip_interrupt_enable(pm8001_ha);
>  4305          spin_unlock_irqrestore(&pm8001_ha->lock, flags);
>
> Probably we should just be doing a spin_lock() and spin_unlock()
> without re-enabling the IRQs.  Should we even be doing that in the
> irq handler anyway?
>
> regards,
> dan carpenter
>
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