[PATCH] io-mapping: Indicate mapping failure

[PATCH] io-mapping: Indicate mapping failure

[Michael J. Ruhl]

Sometimes it is good to know when your mapping failed.

Fixes: cafaf14a5d8f ("io-mapping: Always create a struct to hold metadata about the io-mapping"
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@vger.kernel.org
Signed-off-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
---
 include/linux/io-mapping.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/io-mapping.h b/include/linux/io-mapping.h
index 0beaa3eba155..5641e06cbcf7 100644
--- a/include/linux/io-mapping.h
+++ b/include/linux/io-mapping.h
@@ -118,7 +118,7 @@ io_mapping_init_wc(struct io_mapping *iomap,
 	iomap->prot = pgprot_noncached(PAGE_KERNEL);
 #endif
 
-	return iomap;
+	return iomap->iomem ? iomap : NULL;
 }
 
 static inline void
-- 
2.21.0

Re: [PATCH] io-mapping: Indicate mapping failure

[Andy Shevchenko]

On Tue, Jul 21, 2020 at 10:16:41AM -0400, Michael J. Ruhl wrote:
> Sometimes it is good to know when your mapping failed.

Can you elaborate...

> Fixes: cafaf14a5d8f ("io-mapping: Always create a struct to hold metadata about the io-mapping"

...especially taking into account that Fixes implies regression / bug?

-- 
With Best Regards,
Andy Shevchenko

RE: [PATCH] io-mapping: Indicate mapping failure

[Ruhl, Michael J]

>-----Original Message-----
>From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
>Sent: Tuesday, July 21, 2020 10:47 AM
>To: Ruhl, Michael J <michael.j.ruhl@intel.com>
>Cc: dri-devel@lists.freedesktop.org; Andrew Morton <akpm@linux-
>foundation.org>; Mike Rapoport <rppt@linux.ibm.com>; Chris Wilson
><chris@chris-wilson.co.uk>; stable@vger.kernel.org
>Subject: Re: [PATCH] io-mapping: Indicate mapping failure
>
>On Tue, Jul 21, 2020 at 10:16:41AM -0400, Michael J. Ruhl wrote:
>> Sometimes it is good to know when your mapping failed.
>
>Can you elaborate...

Sure, guess I was too glib. 😊

Currently  the io_mapping_init_wc (the !ATOMIC_IOMAP version), function will
always return success.

If the setting of the iomem (from ioremap_wc) fails, the only way for the 
caller to know is to check the value of iomap->iomem.

Since all of the callers expect a NULL return on error, and check for a NULL,
I felt this needed a fixes (i.e. unexpected behavior).

>> Fixes: cafaf14a5d8f ("io-mapping: Always create a struct to hold metadata
>about the io-mapping"
>
>...especially taking into account that Fixes implies regression / bug?

The failure (in my case a crash) is not revealed until the address is accessed
long after the init.

I will update the commit.

Mike

>--
>With Best Regards,
>Andy Shevchenko
>

Re: [PATCH] io-mapping: Indicate mapping failure

[Mike Rapoport]

On Tue, Jul 21, 2020 at 03:00:41PM +0000, Ruhl, Michael J wrote:
> >-----Original Message-----
> >From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> >Sent: Tuesday, July 21, 2020 10:47 AM
> >To: Ruhl, Michael J <michael.j.ruhl@intel.com>
> >Cc: dri-devel@lists.freedesktop.org; Andrew Morton <akpm@linux-
> >foundation.org>; Mike Rapoport <rppt@linux.ibm.com>; Chris Wilson
> ><chris@chris-wilson.co.uk>; stable@vger.kernel.org
> >Subject: Re: [PATCH] io-mapping: Indicate mapping failure
> >
> >On Tue, Jul 21, 2020 at 10:16:41AM -0400, Michael J. Ruhl wrote:
> >> Sometimes it is good to know when your mapping failed.

I was going to say it's always a good idea ;-)

> >Can you elaborate...
> 
> Sure, guess I was too glib. 😊
> 
> Currently  the io_mapping_init_wc (the !ATOMIC_IOMAP version), function will
> always return success.
> 
> If the setting of the iomem (from ioremap_wc) fails, the only way for the 
> caller to know is to check the value of iomap->iomem.
> 
> Since all of the callers expect a NULL return on error, and check for a NULL,
> I felt this needed a fixes (i.e. unexpected behavior).
> 
> >> Fixes: cafaf14a5d8f ("io-mapping: Always create a struct to hold metadata
> >about the io-mapping"
> >
> >...especially taking into account that Fixes implies regression / bug?
> 
> The failure (in my case a crash) is not revealed until the address is accessed
> long after the init.
> 
> I will update the commit.
> 
> Mike
> 
> >--
> >With Best Regards,
> >Andy Shevchenko
> >
> 

-- 
Sincerely yours,
Mike.