[patch 2/6] scsi: warn and avoid creating dma caches if DMA support is disabled

[patch 2/6] scsi: warn and avoid creating dma caches if DMA support is disabled

[David Rientjes]

__GFP_DMA may not be passed to scsi_{get,put}_host_cmd_pool() if
CONFIG_ZONE_DMA is disabled, which is now possible on x86.  If passed,
emit a warning and return.

Signed-off-by: David Rientjes <rientjes@google.com>
---
 drivers/scsi/scsi.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -359,6 +359,11 @@ EXPORT_SYMBOL(scsi_put_command);
 static struct scsi_host_cmd_pool *scsi_get_host_cmd_pool(gfp_t gfp_mask)
 {
 	struct scsi_host_cmd_pool *retval = NULL, *pool;
+
+#ifndef CONFIG_ZONE_DMA
+	if (WARN_ON_ONCE(gfp_mask & __GFP_DMA))
+		return NULL;
+#endif
 	/*
 	 * Select a command slab for this host and create it if not
 	 * yet existent.
@@ -393,6 +398,10 @@ static void scsi_put_host_cmd_pool(gfp_t gfp_mask)
 {
 	struct scsi_host_cmd_pool *pool;
 
+#ifndef CONFIG_ZONE_DMA
+        if (WARN_ON_ONCE(gfp_mask & __GFP_DMA))
+                return;
+#endif
 	mutex_lock(&host_cmd_pool_mutex);
 	pool = (gfp_mask & __GFP_DMA) ? &scsi_cmd_dma_pool :
 		&scsi_cmd_pool;

[patch 3/6] scsi, fnic: require DMA support for Cisco FNIC

[David Rientjes]

The Cisco FNIC driver requires creating a SLAB_CACHE_DMA cache, which is
not possible if CONFIG_ZONE_DMA is disasbled.  Avoid compiling it without
DMA support.

Signed-off-by: David Rientjes <rientjes@google.com>
---
 drivers/scsi/Kconfig |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/scsi/Kconfig b/drivers/scsi/Kconfig
--- a/drivers/scsi/Kconfig
+++ b/drivers/scsi/Kconfig
@@ -688,7 +688,7 @@ config FCOE
 
 config FCOE_FNIC
 	tristate "Cisco FNIC Driver"
-	depends on PCI && X86
+	depends on PCI && X86 && ZONE_DMA
 	select LIBFCOE
 	help
 	  This is support for the Cisco PCI-Express FCoE HBA.

Re: [patch 3/6] scsi, fnic: require DMA support for Cisco FNIC

[Christoph Hellwig]

On Tue, May 24, 2011 at 04:53:50PM -0700, David Rientjes wrote:
> The Cisco FNIC driver requires creating a SLAB_CACHE_DMA cache, which is
> not possible if CONFIG_ZONE_DMA is disasbled.  Avoid compiling it without
> DMA support.

And you're sure it actually needs it and isn't some sort of typo?  It
might help to Cc the maintainer to figure that out.

Re: [patch 3/6] scsi, fnic: require DMA support for Cisco FNIC

[Roland Dreier]

On Wed, May 25, 2011 at 1:04 AM, Christoph Hellwig <hch@infradead.org> wrote:
>> The Cisco FNIC driver requires creating a SLAB_CACHE_DMA cache, which is
>> not possible if CONFIG_ZONE_DMA is disasbled.  Avoid compiling it without
>> DMA support.
>
> And you're sure it actually needs it and isn't some sort of typo?  It
> might help to Cc the maintainer to figure that out.

Yes, almost certainly it is due to a misunderstanding of what
SLAB_CACHE_DMA means.
(fnic is a modern PCIe device that doesn't have 24-bit DMA restrictions ;)

So the correct fix would likely be to delete the SLAB_CACHE_DMA from the driver.

In any case cc'ing Cisco people as hch suggested...

 - R.

RE: [patch 3/6] scsi, fnic: require DMA support for Cisco FNIC

[Abhijeet Joglekar (abjoglek)]

> -----Original Message-----
> From: roland@purestorage.com [mailto:roland@purestorage.com] On Behalf
> Of Roland Dreier
> Sent: Wednesday, May 25, 2011 12:29 PM
> To: Christoph Hellwig
> Cc: David Rientjes; James E.J. Bottomley; Pekka Enberg; Christoph
> Lameter; linux-scsi@vger.kernel.org; linux-kernel@vger.kernel.org;
> Abhijeet Joglekar (abjoglek); Joe Eykholt
> Subject: Re: [patch 3/6] scsi, fnic: require DMA support for Cisco FNIC
> 
> On Wed, May 25, 2011 at 1:04 AM, Christoph Hellwig <hch@infradead.org>
> wrote:
> >> The Cisco FNIC driver requires creating a SLAB_CACHE_DMA cache,
> which is
> >> not possible if CONFIG_ZONE_DMA is disasbled.  Avoid compiling it
> without
> >> DMA support.
> >
> > And you're sure it actually needs it and isn't some sort of typo?  It
> > might help to Cc the maintainer to figure that out.
> 
> Yes, almost certainly it is due to a misunderstanding of what
> SLAB_CACHE_DMA means.
> (fnic is a modern PCIe device that doesn't have 24-bit DMA restrictions
> ;)
> 
> So the correct fix would likely be to delete the SLAB_CACHE_DMA from
> the driver.
> 
> In any case cc'ing Cisco people as hch suggested...
> 
>  - R.

You are right, fnic hardware does not have any 24-bit DMA restrictions. When I coded it up, I misunderstood the flag as something that is required for allocating memory that hardware DMAs in/out of.

As Roland indicated, the correct fix would be to remove the SLAB_CACHE_DMA flag from the call to kmem_cache, and the GFP_DMA from the call to the mempool allocation routine.

I can create a patch (attributing the fix to David and Roland) and send out for review. Or if David wants, he can modify the patch he submitted to include this fix. David, please let me know how you want to proceed.

Thanks
-- abhijeet

RE: [patch 3/6] scsi, fnic: require DMA support for Cisco FNIC

[David Rientjes]

On Wed, 25 May 2011, Abhijeet Joglekar (abjoglek) wrote:

> As Roland indicated, the correct fix would be to remove the 
> SLAB_CACHE_DMA flag from the call to kmem_cache, and the GFP_DMA from 
> the call to the mempool allocation routine.
> 
> I can create a patch (attributing the fix to David and Roland) and send 
> out for review. Or if David wants, he can modify the patch he submitted 
> to include this fix. David, please let me know how you want to proceed.
> 

It'd be great if you could create a patch, you would certainly be able to 
speak with more authority on the hardware requirements in the changelog 
than I would :)

Thanks Roland, Christoph, and Abhijeet!