diff mbox

[v2] dax: fix NULL pointer in __dax_pmd_fault()

Message ID 1442950582-10140-1-git-send-email-ross.zwisler@linux.intel.com
State New
Headers show

Commit Message

Ross Zwisler Sept. 22, 2015, 7:36 p.m. UTC
The following commit:

commit 46c043ede471 ("mm: take i_mmap_lock in unmap_mapping_range() for
	DAX")

moved some code in __dax_pmd_fault() that was responsible for zeroing
newly allocated PMD pages.  The new location didn't properly set up
'kaddr', though, so when run this code resulted in a NULL pointer BUG.

Fix this by getting the correct 'kaddr' via bdev_direct_access().

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reported-by: Dan Williams <dan.j.williams@intel.com>
---
 fs/dax.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

Comments

Dan Williams Sept. 22, 2015, 8:51 p.m. UTC | #1
[ adding Andrew ]

On Tue, Sep 22, 2015 at 12:36 PM, Ross Zwisler
<ross.zwisler@linux.intel.com> wrote:
> The following commit:
>
> commit 46c043ede471 ("mm: take i_mmap_lock in unmap_mapping_range() for
>         DAX")
>
> moved some code in __dax_pmd_fault() that was responsible for zeroing
> newly allocated PMD pages.  The new location didn't properly set up
> 'kaddr', though, so when run this code resulted in a NULL pointer BUG.
>
> Fix this by getting the correct 'kaddr' via bdev_direct_access().
>
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> Reported-by: Dan Williams <dan.j.williams@intel.com>

Taking into account the comment below,

Reviewed-by: Dan Williams <dan.j.williams@intel.com>

> ---
>  fs/dax.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 7ae6df7..bcfb14b 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -569,8 +569,20 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
>         if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE)
>                 goto fallback;
>
> +       sector = bh.b_blocknr << (blkbits - 9);
> +
>         if (buffer_unwritten(&bh) || buffer_new(&bh)) {
>                 int i;
> +
> +               length = bdev_direct_access(bh.b_bdev, sector, &kaddr, &pfn,
> +                                               bh.b_size);
> +               if (length < 0) {
> +                       result = VM_FAULT_SIGBUS;
> +                       goto out;
> +               }
> +               if ((length < PMD_SIZE) || (pfn & PG_PMD_COLOUR))
> +                       goto fallback;
> +

Hmm, we don't need the PG_PMD_COLOUR check since we aren't using the
pfn in this path, right?
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Dan Williams Sept. 22, 2015, 9:26 p.m. UTC | #2
On Tue, Sep 22, 2015 at 2:17 PM, Ross Zwisler
<ross.zwisler@linux.intel.com> wrote:
> On Tue, Sep 22, 2015 at 01:51:04PM -0700, Dan Williams wrote:
>> [ adding Andrew ]
>>
>> On Tue, Sep 22, 2015 at 12:36 PM, Ross Zwisler
>> <ross.zwisler@linux.intel.com> wrote:
>> > The following commit:
>> >
>> > commit 46c043ede471 ("mm: take i_mmap_lock in unmap_mapping_range() for
>> >         DAX")
>> >
>> > moved some code in __dax_pmd_fault() that was responsible for zeroing
>> > newly allocated PMD pages.  The new location didn't properly set up
>> > 'kaddr', though, so when run this code resulted in a NULL pointer BUG.
>> >
>> > Fix this by getting the correct 'kaddr' via bdev_direct_access().
>> >
>> > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
>> > Reported-by: Dan Williams <dan.j.williams@intel.com>
>>
>> Taking into account the comment below,
>>
>> Reviewed-by: Dan Williams <dan.j.williams@intel.com>
>>
>> > ---
>> >  fs/dax.c | 13 ++++++++++++-
>> >  1 file changed, 12 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/fs/dax.c b/fs/dax.c
>> > index 7ae6df7..bcfb14b 100644
>> > --- a/fs/dax.c
>> > +++ b/fs/dax.c
>> > @@ -569,8 +569,20 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
>> >         if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE)
>> >                 goto fallback;
>> >
>> > +       sector = bh.b_blocknr << (blkbits - 9);
>> > +
>> >         if (buffer_unwritten(&bh) || buffer_new(&bh)) {
>> >                 int i;
>> > +
>> > +               length = bdev_direct_access(bh.b_bdev, sector, &kaddr, &pfn,
>> > +                                               bh.b_size);
>> > +               if (length < 0) {
>> > +                       result = VM_FAULT_SIGBUS;
>> > +                       goto out;
>> > +               }
>> > +               if ((length < PMD_SIZE) || (pfn & PG_PMD_COLOUR))
>> > +                       goto fallback;
>> > +
>>
>> Hmm, we don't need the PG_PMD_COLOUR check since we aren't using the
>> pfn in this path, right?
>
> I think we care, because we'll end up bailing anyway at the later
> PG_PMD_COLOUR check before we actually insert the pfn via
> vmf_insert_pfn_pmd().  If we don't check the alignment we'll do 2 MiB worth of
> zeroing to the media, then later fall back to PTE faults.

Ok, good point.
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diff mbox

Patch

diff --git a/fs/dax.c b/fs/dax.c
index 7ae6df7..bcfb14b 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -569,8 +569,20 @@  int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
 	if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE)
 		goto fallback;
 
+	sector = bh.b_blocknr << (blkbits - 9);
+
 	if (buffer_unwritten(&bh) || buffer_new(&bh)) {
 		int i;
+
+		length = bdev_direct_access(bh.b_bdev, sector, &kaddr, &pfn,
+						bh.b_size);
+		if (length < 0) {
+			result = VM_FAULT_SIGBUS;
+			goto out;
+		}
+		if ((length < PMD_SIZE) || (pfn & PG_PMD_COLOUR))
+			goto fallback;
+
 		for (i = 0; i < PTRS_PER_PMD; i++)
 			clear_pmem(kaddr + i * PAGE_SIZE, PAGE_SIZE);
 		wmb_pmem();
@@ -623,7 +635,6 @@  int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
 		result = VM_FAULT_NOPAGE;
 		spin_unlock(ptl);
 	} else {
-		sector = bh.b_blocknr << (blkbits - 9);
 		length = bdev_direct_access(bh.b_bdev, sector, &kaddr, &pfn,
 						bh.b_size);
 		if (length < 0) {