linux-kernel - Re: [PATCH] Ceph: Avoid data inconsistency due to d-cache aliasing in readpage()

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Date:	Wed, 13 Nov 2013 22:37:17 +0800
From:	Li Wang <liwang@...ntukylin.com>
To:	"Yan, Zheng" <ukernel@...il.com>
CC:	ceph-devel <ceph-devel@...r.kernel.org>,
	Sage Weil <sage@...tank.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Ceph: Avoid data inconsistency due to d-cache aliasing
 in readpage()

Hi Yan,
   zero_user_segment() has invoked flush_dcache_page() for us, we donnot 
wanna flush d-cache twice.

Cheers,
Li Wang

On 11/13/2013 09:19 PM, Yan, Zheng wrote:
> On Wed, Nov 13, 2013 at 3:22 PM, Li Wang <liwang@...ntukylin.com> wrote:
>> If the length of data to be read in readpage() is exactly
>> PAGE_CACHE_SIZE, the original code does not flush d-cache
>> for data consistency after finishing reading. This patches fixes
>> this.
>>
>> Signed-off-by: Li Wang <liwang@...ntukylin.com>
>> ---
>>   fs/ceph/addr.c |    8 ++++++--
>>   1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
>> index 6df8bd4..7b0000a 100644
>> --- a/fs/ceph/addr.c
>> +++ b/fs/ceph/addr.c
>> @@ -210,9 +210,13 @@ static int readpage_nounlock(struct file *filp, struct page *page)
>>          if (err < 0) {
>>                  SetPageError(page);
>>                  goto out;
>> -       } else if (err < PAGE_CACHE_SIZE) {
>> +       } else {
>> +               if (err < PAGE_CACHE_SIZE) {
>>                  /* zero fill remainder of page */
>> -               zero_user_segment(page, err, PAGE_CACHE_SIZE);
>> +                       zero_user_segment(page, err, PAGE_CACHE_SIZE);
>> +               } else {
>> +                       flush_dcache_page(page);
>> +               }
>
> this doesn't make sense for me. why not call flush_dcache_page unconditionally?
>
> Regards
> Yan, Zheng
>>          }
>>          SetPageUptodate(page);
>>
>> --
>> 1.7.9.5
>>
>> --
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