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Subject[PATCH v3 for v5.9] mm/page_alloc: handle a missing case for memalloc_nocma_{save/restore} APIs
Date
From: Joonsoo Kim <iamjoonsoo.kim@lge.com>

memalloc_nocma_{save/restore} APIs can be used to skip page allocation
on CMA area, but, there is a missing case and the page on CMA area could
be allocated even if APIs are used. This patch handles this case to fix
the potential issue.

For now, these APIs are used to prevent long-term pinning on the CMA page.
When the long-term pinning is requested on the CMA page, it is migrated to
the non-CMA page before pinning. This non-CMA page is allocated by using
memalloc_nocma_{save/restore} APIs. If APIs doesn't work as intended,
the CMA page is allocated and it is pinned for a long time. This long-term
pin for the CMA page causes cma_alloc() failure and it could result in
wrong behaviour on the device driver who uses the cma_alloc().

Missing case is an allocation from the pcplist. MIGRATE_MOVABLE pcplist
could have the pages on CMA area so we need to skip it if ALLOC_CMA isn't
specified.

Fixes: 8510e69c8efe (mm/page_alloc: fix memalloc_nocma_{save/restore} APIs)
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
---
mm/page_alloc.c | 19 ++++++++++++++++---
1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index fab5e97..b5a3f18 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3367,9 +3367,16 @@ struct page *rmqueue(struct zone *preferred_zone,
struct page *page;

if (likely(order == 0)) {
- page = rmqueue_pcplist(preferred_zone, zone, gfp_flags,
+ /*
+ * MIGRATE_MOVABLE pcplist could have the pages on CMA area and
+ * we need to skip it when CMA area isn't allowed.
+ */
+ if (!IS_ENABLED(CONFIG_CMA) || alloc_flags & ALLOC_CMA ||
+ migratetype != MIGRATE_MOVABLE) {
+ page = rmqueue_pcplist(preferred_zone, zone, gfp_flags,
migratetype, alloc_flags);
- goto out;
+ goto out;
+ }
}

/*
@@ -3381,7 +3388,13 @@ struct page *rmqueue(struct zone *preferred_zone,

do {
page = NULL;
- if (alloc_flags & ALLOC_HARDER) {
+ /*
+ * order-0 request can reach here when the pcplist is skipped
+ * due to non-CMA allocation context. HIGHATOMIC area is
+ * reserved for high-order atomic allocation, so order-0
+ * request should skip it.
+ */
+ if (order > 0 && alloc_flags & ALLOC_HARDER) {
page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);
if (page)
trace_mm_page_alloc_zone_locked(page, order, migratetype);
--
2.7.4
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