Re: [PATCH v2] mm/page_vma_mapped_walk: Use ptep_get_lockless() for lockless access

[Alexander Gordeev <agordeev@linux.ibm.com>]

On Fri, May 08, 2026 at 01:00:40AM +0000, Wei Yang wrote:
> On Thu, May 07, 2026 at 12:32:09PM +0200, Alexander Gordeev wrote:
> >On Thu, May 07, 2026 at 09:34:33AM +0000, Wei Yang wrote:
> >> >@@ -310,7 +310,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
> >> > 				goto restart;
> >> > 			}
> >> > 			pvmw->pte++;
> >> >-		} while (pte_none(ptep_get(pvmw->pte)));
> >> >+		} while (pte_none(ptep_get_lockless(pvmw->pte)));
> >> 
> >> As Oscar mentioned in lkml.org/lkml/2026/4/27/630, map_pte() may take the
> >> lock. So probably it is not right?
> >
> >If I read the code correctly map_pte() might take the lock, but also
> >might not take it. If it took the lock and uses ptep_get_lockless(),
> >then it is fine. But if it did not take the lock and uses ptep_get(),
> >then it is an issue.
> >
> 
> So the rule here is:
> 
>   * ptep_get_lockless() could be used for locked and not locked
>   * ptep_get() only used when locked
> 
> Right?

Yes, this is my assumption.

> >> > 
> >> > 		if (!pvmw->ptl) {
> >> > 			spin_lock(ptl);
> >> >-- 
> >> >2.51.0
> >> >
> >> 
> >> -- 
> >> Wei Yang
> >
> >Thanks!
> 
> -- 
> Wei Yang
> Help you, Help me