[PATCH 1/2] mm: page-isolation: skip isolated pageblock in start_isolate_page_range()

[Zi Yan <zi.yan@xxxxxxxx>]

From: Zi Yan <ziy@xxxxxxxxxx>

start_isolate_page_range() first isolates the first and the last
pageblocks in the range and ensure pages across range boundaries are split
during isolation. But it missed the case when the range is <= a pageblock
and the first and the last pageblocks are the same one, so the second
isolate_single_pageblock() will always fail. To fix it, skip the pageblock
isolation in second isolate_single_pageblock().

Fixes: 88ee134320b8 ("mm: fix a potential infinite loop in start_isolate_page_range()")
Reported-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Tested-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Link: https://lore.kernel.org/linux-mm/ac65adc0-a7e4-cdfe-a0d8-757195b86293@xxxxxxxxxxx/

Reported-by: Michael Walle <michael@xxxxxxxx>
Tested-by: Michael Walle <michael@xxxxxxxx>
Link: https://lore.kernel.org/linux-mm/8ca048ca8b547e0dd1c95387ee05c23d@xxxxxxxx/

Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
---
 mm/page_isolation.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index c643c8420809..fbd820b21292 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -300,7 +300,7 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
  * the in-use page then splitting the free page.
  */
 static int isolate_single_pageblock(unsigned long boundary_pfn, int flags,
-			gfp_t gfp_flags, bool isolate_before)
+			gfp_t gfp_flags, bool isolate_before, bool skip_isolation)
 {
 	unsigned char saved_mt;
 	unsigned long start_pfn;
@@ -327,11 +327,16 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, int flags,
 				      zone->zone_start_pfn);
 
 	saved_mt = get_pageblock_migratetype(pfn_to_page(isolate_pageblock));
-	ret = set_migratetype_isolate(pfn_to_page(isolate_pageblock), saved_mt, flags,
-			isolate_pageblock, isolate_pageblock + pageblock_nr_pages);
 
-	if (ret)
-		return ret;
+	if (skip_isolation)
+		VM_BUG_ON(!is_migrate_isolate(saved_mt));
+	else {
+		ret = set_migratetype_isolate(pfn_to_page(isolate_pageblock), saved_mt, flags,
+				isolate_pageblock, isolate_pageblock + pageblock_nr_pages);
+
+		if (ret)
+			return ret;
+	}
 
 	/*
 	 * Bail out early when the to-be-isolated pageblock does not form
@@ -463,7 +468,8 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, int flags,
 	return 0;
 failed:
 	/* restore the original migratetype */
-	unset_migratetype_isolate(pfn_to_page(isolate_pageblock), saved_mt);
+	if (!skip_isolation)
+		unset_migratetype_isolate(pfn_to_page(isolate_pageblock), saved_mt);
 	return -EBUSY;
 }
 
@@ -522,14 +528,18 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
 	unsigned long isolate_start = ALIGN_DOWN(start_pfn, pageblock_nr_pages);
 	unsigned long isolate_end = ALIGN(end_pfn, pageblock_nr_pages);
 	int ret;
+	bool skip_isolation = false;
 
 	/* isolate [isolate_start, isolate_start + pageblock_nr_pages) pageblock */
-	ret = isolate_single_pageblock(isolate_start, flags, gfp_flags, false);
+	ret = isolate_single_pageblock(isolate_start, flags, gfp_flags, false, skip_isolation);
 	if (ret)
 		return ret;
 
+	if (isolate_start == isolate_end - pageblock_nr_pages)
+		skip_isolation = true;
+
 	/* isolate [isolate_end - pageblock_nr_pages, isolate_end) pageblock */
-	ret = isolate_single_pageblock(isolate_end, flags, gfp_flags, true);
+	ret = isolate_single_pageblock(isolate_end, flags, gfp_flags, true, skip_isolation);
 	if (ret) {
 		unset_migratetype_isolate(pfn_to_page(isolate_start), migratetype);
 		return ret;
-- 
2.35.1