In strict mode, we should return 0 if there is any hole in pageblock. If
we successfully isolated pages at beginning at pageblock and then have a
bogus compound_order outside pageblock in next page. We will abort search
loop with blockpfn > end_pfn. Although we will limit blockpfn to end_pfn,
we will treat it as a successful isolation in strict mode as blockpfn is
not < end_pfn and return partial isolated pages. Then
isolate_freepages_range may success unexpectly with hole in isolated
range.
Fixes: 9fcd6d2e052ee ("mm, compaction: skip compound pages by order in free scanner")
Signed-off-by: Kemeng Shi <[email protected]>
---
mm/compaction.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c
index a40550a33aee..b4d03c9ffe7c 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -631,6 +631,14 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
page += (1UL << order) - 1;
nr_scanned += (1UL << order) - 1;
}
+ /*
+ * There is a tiny chance that we have read bogus
+ * compound_order(), so be careful to not go outside
+ * of the pageblock.
+ */
+ if (unlikely(blockpfn >= end_pfn))
+ blockpfn = end_pfn - 1;
+
goto isolate_fail;
}
@@ -678,8 +686,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
spin_unlock_irqrestore(&cc->zone->lock, flags);
/*
- * There is a tiny chance that we have read bogus compound_order(),
- * so be careful to not go outside of the pageblock.
+ * Be careful to not go outside of the pageblock.
*/
if (unlikely(blockpfn > end_pfn))
blockpfn = end_pfn;
--
2.30.0
On Sat, Aug 26, 2023 at 11:36:13PM +0800, Kemeng Shi wrote:
> In strict mode, we should return 0 if there is any hole in pageblock. If
> we successfully isolated pages at beginning at pageblock and then have a
> bogus compound_order outside pageblock in next page. We will abort search
> loop with blockpfn > end_pfn. Although we will limit blockpfn to end_pfn,
> we will treat it as a successful isolation in strict mode as blockpfn is
> not < end_pfn and return partial isolated pages. Then
> isolate_freepages_range may success unexpectly with hole in isolated
> range.
>
> Fixes: 9fcd6d2e052ee ("mm, compaction: skip compound pages by order in free scanner")
> Signed-off-by: Kemeng Shi <[email protected]>
Modify the (likely(order <= MAX_ORDER)) block to avoid ever updating
blockpfn past the end of the pageblock. Then remove the second redundant
check.
--
Mel Gorman
SUSE Labs
on 8/29/2023 5:39 PM, Mel Gorman wrote:
> On Sat, Aug 26, 2023 at 11:36:13PM +0800, Kemeng Shi wrote:
>> In strict mode, we should return 0 if there is any hole in pageblock. If
>> we successfully isolated pages at beginning at pageblock and then have a
>> bogus compound_order outside pageblock in next page. We will abort search
>> loop with blockpfn > end_pfn. Although we will limit blockpfn to end_pfn,
>> we will treat it as a successful isolation in strict mode as blockpfn is
>> not < end_pfn and return partial isolated pages. Then
>> isolate_freepages_range may success unexpectly with hole in isolated
>> range.
>>
>> Fixes: 9fcd6d2e052ee ("mm, compaction: skip compound pages by order in free scanner")
>> Signed-off-by: Kemeng Shi <[email protected]>
>
> Modify the (likely(order <= MAX_ORDER)) block to avoid ever updating
> blockpfn past the end of the pageblock. Then remove the second redundant
> check.
>
Sure, I will improve this in next version.