[PATCH alexv12 1/2] mm/compaction: fix isolate_migratepages_block() fails

[Hugh Dickins <hughd@google.com>]

Fix lots of crashes under compaction load: isolate_migratepages_block()
must clean up appropriately when rejecting a page, setting PageLRU again
if it had been cleared; and a put_page() after get_page_unless_zero()
cannot safely be done while holding locked_lruvec - it may turn out to
be the final put_page(), which will take an lruvec lock when PageLRU.

Signed-off-by: Hugh Dickins <hughd@google.com>
---
These fixes should be folded into 10/16 and 12/16,
I have not tried to figure out what belongs in which.

 mm/compaction.c |   24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

--- alexv12/mm/compaction.c	2020-06-11 13:24:52.037154793 -0700
+++ hughd/mm/compaction.c	2020-06-11 13:48:10.437046025 -0700
@@ -879,6 +879,7 @@ isolate_migratepages_block(struct compac
 		if (!valid_page && IS_ALIGNED(low_pfn, pageblock_nr_pages)) {
 			if (!cc->ignore_skip_hint && get_pageblock_skip(page)) {
 				low_pfn = end_pfn;
+				page = NULL;
 				goto isolate_abort;
 			}
 			valid_page = page;
@@ -971,10 +972,8 @@ isolate_migratepages_block(struct compac
 			goto isolate_fail;
 
 		/* Try isolate the page */
-		if (!TestClearPageLRU(page)) {
-			put_page(page);
-			goto isolate_fail;
-		}
+		if (!TestClearPageLRU(page))
+			goto isolate_fail_put;
 
 		rcu_read_lock();
 		lruvec = mem_cgroup_page_lruvec(page, pgdat);
@@ -1005,7 +1004,8 @@ isolate_migratepages_block(struct compac
 			 */
 			if (unlikely(PageCompound(page) && !cc->alloc_contig)) {
 				low_pfn += compound_nr(page) - 1;
-				goto isolate_fail;
+				SetPageLRU(page);
+				goto isolate_fail_put;
 			}
 		} else
 			rcu_read_unlock();
@@ -1038,6 +1038,15 @@ isolate_success:
 		}
 
 		continue;
+
+isolate_fail_put:
+		/* Avoid potential deadlock in freeing page under lru_lock */
+		if (locked_lruvec) {
+			unlock_page_lruvec_irqrestore(locked_lruvec, flags);
+			locked_lruvec = NULL;
+		}
+		put_page(page);
+
 isolate_fail:
 		if (!skip_on_failure)
 			continue;
@@ -1074,10 +1083,15 @@ isolate_fail:
 	 */
 	if (unlikely(low_pfn > end_pfn))
 		low_pfn = end_pfn;
+	page = NULL;
 
 isolate_abort:
 	if (locked_lruvec)
 		unlock_page_lruvec_irqrestore(locked_lruvec, flags);
+	if (page) {
+		SetPageLRU(page);
+		put_page(page);
+	}
 
 	/*
 	 * Updated the cached scanner pfn once the pageblock has been scanned