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[PATCH] dax: check return value of dax_radix_entry()

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  [PATCH] dax: check return value of dax_radix_entry() Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-03-01 23:20 +0100
    Re: [PATCH] dax: check return value of dax_radix_entry() Matthew Wilcox <willy@linux.intel.com> - 2016-03-02 15:10 +0100
      Re: [PATCH] dax: check return value of dax_radix_entry() Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-03-02 17:40 +0100

#1347066 — [PATCH] dax: check return value of dax_radix_entry()

dax_pfn_mkwrite() previously wasn't checking the return value of the call
to dax_radix_entry(), which was a mistake.

Instead, capture this return value and pass it up the stack if it is an
error.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/dax.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/dax.c b/fs/dax.c
index 7111724..5a587dc 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1056,6 +1056,7 @@ EXPORT_SYMBOL_GPL(dax_pmd_fault);
 int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
 	struct file *file = vma->vm_file;
+	int error;
 
 	/*
 	 * We pass NO_SECTOR to dax_radix_entry() because we expect that a
@@ -1065,7 +1066,11 @@ int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 	 * saves us from having to make a call to get_block() here to look
 	 * up the sector.
 	 */
-	dax_radix_entry(file->f_mapping, vmf->pgoff, NO_SECTOR, false, true);
+	error = dax_radix_entry(file->f_mapping, vmf->pgoff, NO_SECTOR, false,
+			true);
+	if (error)
+		return error;
+
 	return VM_FAULT_NOPAGE;
 }
 EXPORT_SYMBOL_GPL(dax_pfn_mkwrite);
-- 
2.5.0

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#1348058

On Tue, Mar 01, 2016 at 03:15:08PM -0700, Ross Zwisler wrote:
> dax_pfn_mkwrite() previously wasn't checking the return value of the call
> to dax_radix_entry(), which was a mistake.
> 
> Instead, capture this return value and pass it up the stack if it is an
> error.

>  	 */
> -	dax_radix_entry(file->f_mapping, vmf->pgoff, NO_SECTOR, false, true);
> +	error = dax_radix_entry(file->f_mapping, vmf->pgoff, NO_SECTOR, false,
> +			true);
> +	if (error)
> +		return error;
> +
>  	return VM_FAULT_NOPAGE;

You can't return an errno from here.

	if (error)
		return VM_FAULT_SIGBUS;

is better.  For full points,

	if (error == -ENOMEM)
		return VM_FAULT_OOM;
	if (error)
		return VM_FAULT_SIGBUS;
	return VM_FAULT_NOPAGE;

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#1348309

On Wed, Mar 02, 2016 at 09:09:47AM -0500, Matthew Wilcox wrote:
> On Tue, Mar 01, 2016 at 03:15:08PM -0700, Ross Zwisler wrote:
> > dax_pfn_mkwrite() previously wasn't checking the return value of the call
> > to dax_radix_entry(), which was a mistake.
> > 
> > Instead, capture this return value and pass it up the stack if it is an
> > error.
> 
> >  	 */
> > -	dax_radix_entry(file->f_mapping, vmf->pgoff, NO_SECTOR, false, true);
> > +	error = dax_radix_entry(file->f_mapping, vmf->pgoff, NO_SECTOR, false,
> > +			true);
> > +	if (error)
> > +		return error;
> > +
> >  	return VM_FAULT_NOPAGE;
> 
> You can't return an errno from here.
> 
> 	if (error)
> 		return VM_FAULT_SIGBUS;
> 
> is better.  For full points,
> 
> 	if (error == -ENOMEM)
> 		return VM_FAULT_OOM;
> 	if (error)
> 		return VM_FAULT_SIGBUS;
> 	return VM_FAULT_NOPAGE;

Ah, thank you for catching that.

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