Messages in this thread | | | Date | Fri, 9 Jun 2017 11:05:29 +0100 | From | Will Deacon <> | Subject | Re: [PATCH 2/3] mm/page_ref: Ensure page_ref_unfreeze is ordered against prior accesses |
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On Thu, Jun 08, 2017 at 02:50:59PM +0200, Peter Zijlstra wrote: > On Thu, Jun 08, 2017 at 12:24:33PM +0100, Will Deacon wrote: > > [+ PeterZ] > > > > On Thu, Jun 08, 2017 at 01:07:02PM +0200, Vlastimil Babka wrote: > > > On 06/08/2017 12:40 PM, Kirill A. Shutemov wrote: > > > > On Thu, Jun 08, 2017 at 11:38:21AM +0200, Vlastimil Babka wrote: > > > >> On 06/06/2017 07:58 PM, Will Deacon wrote: > > > >>> include/linux/page_ref.h | 1 + > > > >>> 1 file changed, 1 insertion(+) > > > >>> > > > >>> diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h > > > >>> index 610e13271918..74d32d7905cb 100644 > > > >>> --- a/include/linux/page_ref.h > > > >>> +++ b/include/linux/page_ref.h > > > >>> @@ -174,6 +174,7 @@ static inline void page_ref_unfreeze(struct page *page, int count) > > > >>> VM_BUG_ON_PAGE(page_count(page) != 0, page); > > > >>> VM_BUG_ON(count == 0); > > > >>> > > > >>> + smp_mb__before_atomic(); > > > >>> atomic_set(&page->_refcount, count); > > So depending on what it actually required, we do have > atomic_set_release() (atomic_t equivalent to smp_store_release()).
Yeah, I was wondering about that this morning. I think it should do the trick here, but smp_mb() would be a better fit for the other parts of this API (page_ref_freeze uses atomic_cmpxchg and page_cache_get_speculative uses atomic_add_unless).
I'll send a v2 with the full barrier.
Will
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