linux-kernel - RE: [PATCH 2/2] [SCSI] pm8001: Fix possible racing codition.

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Date:	Mon, 27 Feb 2012 12:48:19 +0800
From:	"Jack Wang" <jack_wang@...sh.com>
To:	"'santosh nayak'" <santoshprasadnayak@...il.com>
Cc:	<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 2/2] [SCSI] pm8001: Fix possible racing codition.

Infact , process_oq is only called in pm8001_chip_isr, but this patch looks
OK for me. Move down the lock to process_oq is OK.

Thanks for fix.
Acked-by : Jack Wang <jack_wang@...sh.com>

> From: Santosh Nayak <santoshprasadnayak@...il.com>
> 
> There is a possble racing scenario.
> 
> 'process_oq' is called by two routines, as shown below.
> 
> pm8001_8001_dispatch = {
>          .......
> 
>         .isr             = pm8001_chip_isr --> process_oq,// A
>         .isr_process_oq  = process_oq,                   //  B
>         .....
> }
> 
> process_oq() --> process_one_iomb() --> mpi_sata_completion()
> 
> In 'mpi_sata_completion', "pm8001_ha->lock" is first released.
> It means lock is taken before,  which is true for
> the context A, as 'pm8001_ha->lock' is taken in 'pm8001_chip_isr()'
> 
> But for context B there is no lock taken before and pm8001_ha->lock
> is unlocked in 'mpi_sata_completion()'. This may unlock the lock
> taken in context A. Possible racing ??
> 
> If 'pm8001_ha->lock' is taken in 'process_oq()' instead of
> 'pm8001_chip_isr' then the above issue can be avoided.
> 
> Signed-off-by: Santosh Nayak <santoshprasadnayak@...il.com>
> ---
>  drivers/scsi/pm8001/pm8001_hwi.c |    6 +++---
>  1 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/scsi/pm8001/pm8001_hwi.c
> b/drivers/scsi/pm8001/pm8001_hwi.c
> index 838e3e2..6d9973b 100644
> --- a/drivers/scsi/pm8001/pm8001_hwi.c
> +++ b/drivers/scsi/pm8001/pm8001_hwi.c
> @@ -3663,7 +3663,9 @@ static int process_oq(struct pm8001_hba_info
*pm8001_ha)
>  	void *pMsg1 = NULL;
>  	u8 uninitialized_var(bc);
>  	u32 ret = MPI_IO_STATUS_FAIL;
> +	unsigned long flags;
> 
> +	spin_lock_irqsave(&pm8001_ha->lock, flags);
>  	circularQ = &pm8001_ha->outbnd_q_tbl[0];
>  	do {
>  		ret = mpi_msg_consume(pm8001_ha, circularQ, &pMsg1, &bc);
> @@ -3682,6 +3684,7 @@ static int process_oq(struct pm8001_hba_info
*pm8001_ha)
>  				break;
>  		}
>  	} while (1);
> +	spin_unlock_irqrestore(&pm8001_ha->lock, flags);
>  	return ret;
>  }
> 
> @@ -4087,12 +4090,9 @@ static u32 pm8001_chip_is_our_interupt(struct
> pm8001_hba_info *pm8001_ha)
>  static irqreturn_t
>  pm8001_chip_isr(struct pm8001_hba_info *pm8001_ha)
>  {
> -	unsigned long flags;
> -	spin_lock_irqsave(&pm8001_ha->lock, flags);
>  	pm8001_chip_interrupt_disable(pm8001_ha);
>  	process_oq(pm8001_ha);
>  	pm8001_chip_interrupt_enable(pm8001_ha);
> -	spin_unlock_irqrestore(&pm8001_ha->lock, flags);
>  	return IRQ_HANDLED;
>  }
> 
> --
> 1.7.4.4
> 
> --
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