lkml.org 
[lkml]   [2015]   [Sep]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH] mm: take i_mmap_lock in unmap_mapping_range() for DAX
From
On Thu, Sep 17, 2015 at 8:41 AM, Ross Zwisler
<ross.zwisler@linux.intel.com> wrote:
> On Wed, Sep 16, 2015 at 02:12:18PM +0300, Kirill A. Shutemov wrote:
>> On Tue, Sep 15, 2015 at 04:52:42PM -0700, Dan Williams wrote:
>> > Hi Kirill,
>> >
>> > On Fri, Aug 7, 2015 at 4:53 AM, Kirill A. Shutemov
>> > <kirill.shutemov@linux.intel.com> wrote:
>> > > DAX is not so special: we need i_mmap_lock to protect mapping->i_mmap.
>> > >
>> > > __dax_pmd_fault() uses unmap_mapping_range() shoot out zero page from
>> > > all mappings. We need to drop i_mmap_lock there to avoid lock deadlock.
>> > >
>> > > Re-aquiring the lock should be fine since we check i_size after the
>> > > point.
>> > >
>> > > Not-yet-signed-off-by: Matthew Wilcox <willy@linux.intel.com>
>> > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
>> > > ---
>> > > fs/dax.c | 35 +++++++++++++++++++----------------
>> > > mm/memory.c | 11 ++---------
>> > > 2 files changed, 21 insertions(+), 25 deletions(-)
>> > >
>> > > diff --git a/fs/dax.c b/fs/dax.c
>> > > index 9ef9b80cc132..ed54efedade6 100644
>> > > --- a/fs/dax.c
>> > > +++ b/fs/dax.c
>> > > @@ -554,6 +554,25 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
>> > > if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE)
>> > > goto fallback;
>> > >
>> > > + if (buffer_unwritten(&bh) || buffer_new(&bh)) {
>> > > + int i;
>> > > + for (i = 0; i < PTRS_PER_PMD; i++)
>> > > + clear_page(kaddr + i * PAGE_SIZE);
>> >
>> > This patch, now upstream as commit 46c043ede471, moves the call to
>> > clear_page() earlier in __dax_pmd_fault(). However, 'kaddr' is not
>> > set at this point, so I'm not sure this path was ever tested.
>>
>> Ughh. It's obviously broken.
>>
>> I took fs/dax.c part of the patch from Matthew. And I'm not sure now we
>> would need to move this "if (buffer_unwritten(&bh) || buffer_new(&bh)) {"
>> block around. It should work fine where it was before. Right?
>> Matthew?
>
> Moving the "if (buffer_unwritten(&bh) || buffer_new(&bh)) {" block back seems
> correct to me. Matthew is out for a while, so we should probably take care of
> this without him.

I'd say leave it at its current location and add a local call to
bdev_direct_access() as I'm not sure you'd want to trigger one of the
failure conditions without having zeroed the page. I.e. right before
vmf_insert_pfn_pmd() is probably too late.


\
 
 \ /
  Last update: 2015-09-17 18:01    [W:0.058 / U:0.592 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site