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

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Message-ID: <608226F8941E4DE49A175A8B3262BA41@usish.com.cn>
Date:	Mon, 27 Feb 2012 13:06:32 +0800
From:	"Jack Wang" <jack_wang@...sh.com>
To:	"'santosh prasad 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.


The first is not called, just implement a interface, just reserved.

Thanks anyway.
Jack
> 
> 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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in
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> >
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