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

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Date:	Mon, 27 Feb 2012 10:32:01 +0530
From:	santosh prasad nayak <santoshprasadnayak@...il.com>
To:	Jack Wang <jack_wang@...sh.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.

Thanks Jack for your response.

'process_oq'  is called at two places.


 pm8001_8001_dispatch = {
          .......

         .isr             = pm8001_chip_isr --> process_oq,     //   1st place
         .isr_process_oq  = process_oq,                            //
 2nd  place
         .....
}

regards
santosh

On Mon, Feb 27, 2012 at 10:18 AM, Jack Wang <jack_wang@...sh.com> wrote:
> 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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