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Date:   Tue, 22 Jan 2019 10:48:16 +0300
From:   Dan Carpenter <dan.carpenter@oracle.com>
To:     Ching Huang <ching2048@areca.com.tw>
Cc:     martin.petersen@oracle.com, James.Bottomley@HansenPartnership.com,
        linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
        hch@infradead.org, colin.king@canonical.com
Subject: Re: [PATCH 2/3] scsi: arcmsr: Fix suspend/resume of
 ACB_ADAPTER_TYPE_B part 2
Message-ID: <20190122074816.GC11828@kadam>
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 <1547714827.5079.19.camel@Centos6.3-64>
 <20190117091646.GA11828@kadam>
 <1547718748.5079.34.camel@Centos6.3-64>
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On Thu, Jan 17, 2019 at 05:52:28PM +0800, Ching Huang wrote:
> On Thu, 2019-01-17 at 12:16 +0300, Dan Carpenter wrote:
> > On Thu, Jan 17, 2019 at 04:47:07PM +0800, Ching Huang wrote:
> > > On Thu, 2019-01-17 at 10:59 +0300, Dan Carpenter wrote:
> > > > On Thu, Jan 17, 2019 at 11:45:03AM +0800, Ching Huang wrote:
> > > > > >From Ching Huang <ching2048@areca.com.tw>
> > > > > 
> > > > > Fix suspend/resume of ACB_ADAPTER_TYPE_B part 2.
> > > > > 
> > > > 
> > > > What does this look like from a user perspective?  Does it fail every
> > > > time or does it only fail sometimes?
> > > > 
> > > > What's the bug exactly?
> > > > 
> > > > There is no Fixes tag...
> > > >From user's perspective, hibernate/resume are OK.
> > > But following IO may cause 'isr get an illegal ccb command' in
> > > log/messages sometime.
> > > > 
> > 
> > 
> > You will need to resend with that information included in the commit
> > message.
> OK. I will resend this patch later.
> > 
> > > > > Signed-off-by: Ching Huang <ching2048@areca.com.tw>
> > > > > ---
> > > > > 
> > > > > diff --git a/drivers/scsi/arcmsr/arcmsr.h b/drivers/scsi/arcmsr/arcmsr.h
> > > > > index a94c513..b98c632 100755
> > > > > --- a/drivers/scsi/arcmsr/arcmsr.h
> > > > > +++ b/drivers/scsi/arcmsr/arcmsr.h
> > > > > @@ -508,9 +508,9 @@ struct MessageUnit_A
> > > > >  struct MessageUnit_B
> > > > >  {
> > > > >  	uint32_t	post_qbuffer[ARCMSR_MAX_HBB_POSTQUEUE];
> > > > > -	uint32_t	done_qbuffer[ARCMSR_MAX_HBB_POSTQUEUE];
> > > > > +	volatile uint32_t	done_qbuffer[ARCMSR_MAX_HBB_POSTQUEUE];
> > > > 
> > > > There is a well known rule of thumb that when someone uses "volatile"
> > > > in the kernel it means there is a locking problem...  Is this __iomem or
> > > > something?
> > > The done_qbuffer was a command completion queue, it was an area written
> > > by IO processor and read by device driver. So, ...
> > 
> > I'm not totally positive I understand this sentence.  I can find a bunch
> > of places which read from this buffer, but I haven't immediately found
> > which place writes to it.  Can you give me a function name that I should
> > read?
> Well, we allocate memory for struct MessageUnit_B in
> arcmsr_alloc_ccb_pool(), by assign to acb->dma_coherent_handle2.
> Then we tell IO controller its DMA address in arcmsr_iop_confirm().
> When a command was completed, controller's firmware program will write a
> completion ccb in done_qbuffer through DMA. So, you can't see any driver
> funtion write to it.

DMA memory doesn't need to be marked as volatile.

regards,
dan carpenter