Re: [PATCH v2] fix __set_page_dirty_no_writeback() return value

[Bob Liu <lliubbo@gmail.com>]

On Thu, Nov 11, 2010 at 11:02 AM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> On Thu, 11 Nov 2010 11:05:54 +0800 Bob Liu <lliubbo@gmail.com> wrote:
>
>> __set_page_dirty_no_writeback() should return true if it actually transitioned
>> the page from a clean to dirty state although it seems nobody used its return
>> value now.
>>
>> Change from v1:
>>       * preserving cacheline optimisation as Andrew pointed out
>>
>> Signed-off-by: Bob Liu <lliubbo@gmail.com>
>> ---
>>  mm/page-writeback.c |    4 +++-
>>  1 files changed, 3 insertions(+), 1 deletions(-)
>>
>> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
>> index bf85062..ac7018a 100644
>> --- a/mm/page-writeback.c
>> +++ b/mm/page-writeback.c
>> @@ -1157,8 +1157,10 @@ EXPORT_SYMBOL(write_one_page);
>>   */
>>  int __set_page_dirty_no_writeback(struct page *page)
>>  {
>> -     if (!PageDirty(page))
>> +     if (!PageDirty(page)) {
>>               SetPageDirty(page);
>> +             return 1;
>> +     }
>>       return 0;
>>  }
>
> But that has a race.  If someone else sets PG_Dirty between the test
> and the set, this function will incorrectly return 1.
>
> Which is why it should use test_and_set if we're going to do this.
>

Oh, Sorry for that.
I will make a new patch soon.

-- 
Thanks,
--Bob

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