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From:   Levi Yun <ppbuk5246@gmail.com>
To:     akpm@linux-foundation.org
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Levi Yun <ppbuk5246@gmail.com>
Subject: [PATCH] mm/cma: Fix potential memory loss on cma_declare_contiguous_nid
Date:   Wed, 18 Jan 2023 17:05:23 +0900
Message-Id: <20230118080523.44522-1-ppbuk5246@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Suppose, memblock_alloc_ranged_nid with highmem_start is success
when cma_declare_contiguous_nid is called with !fixed
in the system 32-bit system with PHYS_ADDR_T_64BIT enabled
with memblock.bottom_up == false.

But, Next trial to memblock_alloc_range_nid to allocate in
[SIZE_4G, limits) nullifies former success allocated addr and
it retries to memblock_alloc_ragne_nid again.

In this situation, first success address area is lost.

By changing order of allocation (SIZE_4G, high_memory and base) and
checking whether allocated prevents potential memory lost.

Signed-off-by: Levi Yun <ppbuk5246@gmail.com>
---
 mm/cma.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/mm/cma.c b/mm/cma.c
index 4a978e09547a..49d9b08d9a47 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -321,18 +321,6 @@ int __init cma_declare_contiguous_nid(phys_addr_t base,
 	} else {
 		phys_addr_t addr = 0;

-		/*
-		 * All pages in the reserved area must come from the same zone.
-		 * If the requested region crosses the low/high memory boundary,
-		 * try allocating from high memory first and fall back to low
-		 * memory in case of failure.
-		 */
-		if (base < highmem_start && limit > highmem_start) {
-			addr = memblock_alloc_range_nid(size, alignment,
-					highmem_start, limit, nid, true);
-			limit = highmem_start;
-		}
-
 		/*
 		 * If there is enough memory, try a bottom-up allocation first.
 		 * It will place the new cma area close to the start of the node
@@ -350,6 +338,18 @@ int __init cma_declare_contiguous_nid(phys_addr_t base,
 		}
 #endif

+		/*
+		 * All pages in the reserved area must come from the same zone.
+		 * If the requested region crosses the low/high memory boundary,
+		 * try allocating from high memory first and fall back to low
+		 * memory in case of failure.
+		 */
+		if (!addr && base < highmem_start && limit > highmem_start) {
+			addr = memblock_alloc_range_nid(size, alignment,
+					highmem_start, limit, nid, true);
+			limit = highmem_start;
+		}
+
 		if (!addr) {
 			addr = memblock_alloc_range_nid(size, alignment, base,
 					limit, nid, true);
--
2.35.1