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Date: Tue, 11 Apr 2017 13:58:20 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Pushkar Jambhlekar <pushkar.iit@gmail.com>
Cc: Dan Williams <dan.j.williams@intel.com>,
        Dave Jiang <dave.jiang@intel.com>,
        Johannes Thumshirn <jthumshirn@suse.de>,
        Ross Zwisler <ross.zwisler@linux.intel.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] drivers/dax: Changing RC value
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On Tue, 11 Apr 2017 10:56:45 +0530 Pushkar Jambhlekar <pushkar.iit@gmail.com> wrote:

> Changing rc value from VM_FAULT_FALLBACK to VM_FAULT_SIGBUS for an unknown / unsupported fault size.
> 
> ...
>
> --- a/drivers/dax/dax.c
> +++ b/drivers/dax/dax.c
> @@ -590,7 +590,7 @@ static int dax_dev_huge_fault(struct vm_fault *vmf,
>  		rc = __dax_dev_pud_fault(dax_dev, vmf);
>  		break;
>  	default:
> -		rc =  VM_FAULT_FALLBACK;
> +		rc = VM_FAULT_SIGBUS;
>  	}
>  	rcu_read_unlock();

The change seems to make sense but more info would be helpful.  What
is wrong with the current code?  ie, what goes wrong if we return
VM_FAULT_FALLBACK here?