linux-kernel - [PATCH v6 03/14] mm/gup: return an error on migration failure

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Date:   Tue, 19 Jan 2021 20:43:22 -0500
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     pasha.tatashin@...een.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, akpm@...ux-foundation.org, vbabka@...e.cz,
        mhocko@...e.com, david@...hat.com, osalvador@...e.de,
        dan.j.williams@...el.com, sashal@...nel.org,
        tyhicks@...ux.microsoft.com, iamjoonsoo.kim@....com,
        mike.kravetz@...cle.com, rostedt@...dmis.org, mingo@...hat.com,
        jgg@...pe.ca, peterz@...radead.org, mgorman@...e.de,
        willy@...radead.org, rientjes@...gle.com, jhubbard@...dia.com,
        linux-doc@...r.kernel.org, ira.weiny@...el.com,
        linux-kselftest@...r.kernel.org
Subject: [PATCH v6 03/14] mm/gup: return an error on migration failure

When migration failure occurs, we still pin pages, which means
that we may pin CMA movable pages which should never be the case.

Instead return an error without pinning pages when migration failure
happens.

No need to retry migrating, because migrate_pages() already retries
10 times.

Signed-off-by: Pavel Tatashin <pasha.tatashin@...een.com>
Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
---
 mm/gup.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 16f10d5a9eb6..88ce41f41543 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1557,7 +1557,6 @@ static long check_and_migrate_cma_pages(struct mm_struct *mm,
 {
 	unsigned long i;
 	bool drain_allow = true;
-	bool migrate_allow = true;
 	LIST_HEAD(cma_page_list);
 	long ret = nr_pages;
 	struct page *prev_head, *head;
@@ -1608,17 +1607,15 @@ static long check_and_migrate_cma_pages(struct mm_struct *mm,
 			for (i = 0; i < nr_pages; i++)
 				put_page(pages[i]);
 
-		if (migrate_pages(&cma_page_list, alloc_migration_target, NULL,
-			(unsigned long)&mtc, MIGRATE_SYNC, MR_CONTIG_RANGE)) {
-			/*
-			 * some of the pages failed migration. Do get_user_pages
-			 * without migration.
-			 */
-			migrate_allow = false;
-
+		ret = migrate_pages(&cma_page_list, alloc_migration_target,
+				    NULL, (unsigned long)&mtc, MIGRATE_SYNC,
+				    MR_CONTIG_RANGE);
+		if (ret) {
 			if (!list_empty(&cma_page_list))
 				putback_movable_pages(&cma_page_list);
+			return ret > 0 ? -ENOMEM : ret;
 		}
+
 		/*
 		 * We did migrate all the pages, Try to get the page references
 		 * again migrating any new CMA pages which we failed to isolate
@@ -1628,7 +1625,7 @@ static long check_and_migrate_cma_pages(struct mm_struct *mm,
 						   pages, vmas, NULL,
 						   gup_flags);
 
-		if ((ret > 0) && migrate_allow) {
+		if (ret > 0) {
 			nr_pages = ret;
 			drain_allow = true;
 			goto check_again;
-- 
2.25.1