[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 at linux.intel.com>
> >Sent: Tuesday, July 21, 2020 10:47 AM
> >To: Ruhl, Michael J <michael.j.ruhl at intel.com>
> >Cc: dri-devel at lists.freedesktop.org; Andrew Morton <akpm at linux-
> >foundation.org>; Mike Rapoport <rppt at linux.ibm.com>; Chris Wilson
> ><chris at chris-wilson.co.uk>; stable at 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.