Re: [PATCH] msync: fix incorrect fstart calculation

["Lukáš Czerner" <lczerner@redhat.com>]

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On Fri, 27 Jun 2014, Namjae Jeon wrote:

> Date: Fri, 27 Jun 2014 20:38:49 +0900
> From: Namjae Jeon <namjae.jeon@samsung.com>
> To: 'Andrew Morton' <akpm@linux-foundation.org>
> Cc: linux-mm@kvack.org, linux-ext4 <linux-ext4@vger.kernel.org>,
>     Luka1 Czerner <lczerner@redhat.com>,
>     'Matthew Wilcox' <matthew.r.wilcox@intel.com>,
>     'Eric Whitney' <enwlinux@gmail.com>,
>     Ashish Sangwan <a.sangwan@samsung.com>
> Subject: [PATCH] msync: fix incorrect fstart calculation
> 
> Fix a regression caused by Commit 7fc34a62ca mm/msync.c: sync only
> the requested range in msync().
> xfstests generic/075 fail occured on ext4 data=journal mode because
> the intended range was not syncing due to wrong fstart calculation.

Looks good to me and it fixes the issues with data=journal on ext4.

Reviewed-by: Lukas Czerner <lczerner@redhat.com>
Tested-by: Lukas Czerner <lczerner@redhat.com>

> 
> Cc: Matthew Wilcox <matthew.r.wilcox@intel.com>
> Cc: Luka1 Czerner <lczerner@redhat.com>
> Reported-by: Eric Whitney <enwlinux@gmail.com>
> Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
> Signed-off-by: Ashish Sangwan <a.sangwan@samsung.com>
> ---
>  mm/msync.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/msync.c b/mm/msync.c
> index a5c6736..ad97dce 100644
> --- a/mm/msync.c
> +++ b/mm/msync.c
> @@ -78,7 +78,8 @@ SYSCALL_DEFINE3(msync, unsigned long, start, size_t, len, int, flags)
>  			goto out_unlock;
>  		}
>  		file = vma->vm_file;
> -		fstart = start + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
> +		fstart = (start - vma->vm_start) +
> +			 ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
>  		fend = fstart + (min(end, vma->vm_end) - start) - 1;
>  		start = vma->vm_end;
>  		if ((flags & MS_SYNC) && file &&
>