On Tue, 4 Jul 2023 20:36:00 +0800 Miaohe Lin <linmiaohe@xxxxxxxxxx> wrote:
> On 2023/7/4 20:13, Matthew Wilcox wrote:
> > On Tue, Jul 04, 2023 at 07:18:23PM +0800, Miaohe Lin wrote:
> >> @@ -470,6 +470,8 @@ static int page_outside_zone_boundaries(struct zone *zone, struct page *page)
> >> sp = zone->spanned_pages;
> >> if (!zone_spans_pfn(zone, pfn))
> >> ret = 1;
> >> + else
> >> + ret = 0;
> >
> > Surely 'ret = zone_spans_pfn(zone, pfn);' ?
>
> Do you mean 'ret = !zone_spans_pfn(zone, pfn);'? This format looks fine to me.
>
> >
> > Also, did you spot this by inspection or do you have a test-case or bug
> > report? Should this have a Fixes: tag?
>
> This is from code inspection. The race window should be really small thus hard to trigger
> in real world. And yes, it seems Fixes tag is a really ancient commit:
>
> Fixes: bdc8cb984576 ("[PATCH] memory hotplug locking: zone span seqlock")
>
Thanks. I updated the changelog:
: If pfn is outside zone boundaries in the first round, ret will be set to
: 1. But if pfn is changed to inside the zone boundaries in zone span
: seqretry path, ret is still set to 1 leading to false page outside zone
: error info.
:
: This is from code inspection. The race window should be really small thus
: hard to trigger in real world.
:
: Link: https://lkml.kernel.org/r/20230704111823.940331-1-linmiaohe@xxxxxxxxxx
: Fixes: bdc8cb984576 ("[PATCH] memory hotplug locking: zone span seqlock")
and I made the change suggested by Matthew:
--- a/mm/page_alloc.c~mm-page_alloc-avoid-false-page-outside-zone-error-info-fix
+++ a/mm/page_alloc.c
@@ -468,10 +468,7 @@ static int page_outside_zone_boundaries(
seq = zone_span_seqbegin(zone);
start_pfn = zone->zone_start_pfn;
sp = zone->spanned_pages;
- if (!zone_spans_pfn(zone, pfn))
- ret = 1;
- else
- ret = 0;
+ ret = !zone_spans_pfn(zone, pfn);
} while (zone_span_seqretry(zone, seq));
if (ret)
_
