linux-kernel - [PATCH 1/1] mm/percpu.c: correct max_distance calculation for pcpu_embed_first

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Message-ID: <7180d3c9-45d3-ffd2-cf8c-0d925f888a4d@zoho.com>
Date:   Sat, 24 Sep 2016 02:20:24 +0800
From:   zijun_hu <zijun_hu@...o.com>
To:     Tejun Heo <tj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     zijun_hu@....com,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org, cl@...ux.com
Subject: [PATCH 1/1] mm/percpu.c: correct max_distance calculation for
 pcpu_embed_first_chunk()

From: zijun_hu <zijun_hu@....com>

correct max_distance from (base of the highest group + ai->unit_size)
to (base of the highest group + the group size)

Signed-off-by: zijun_hu <zijun_hu@....com>
---
 mm/percpu.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/mm/percpu.c b/mm/percpu.c
index fcaaac977954..ee0d1c93f070 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1963,7 +1963,8 @@ int __init pcpu_embed_first_chunk(size_t reserved_size, size_t dyn_size,
 	void *base = (void *)ULONG_MAX;
 	void **areas = NULL;
 	struct pcpu_alloc_info *ai;
-	size_t size_sum, areas_size, max_distance;
+	size_t size_sum, areas_size;
+	unsigned long max_distance;
 	int group, i, rc;
 
 	ai = pcpu_build_alloc_info(reserved_size, dyn_size, atom_size,
@@ -2025,17 +2026,18 @@ int __init pcpu_embed_first_chunk(size_t reserved_size, size_t dyn_size,
 	}
 
 	/* base address is now known, determine group base offsets */
-	max_distance = 0;
+	i = 0;
 	for (group = 0; group < ai->nr_groups; group++) {
 		ai->groups[group].base_offset = areas[group] - base;
-		max_distance = max_t(size_t, max_distance,
-				     ai->groups[group].base_offset);
+		if (areas[group] > areas[i])
+			i = group;
 	}
-	max_distance += ai->unit_size;
+	max_distance = ai->groups[i].base_offset +
+		(unsigned long)ai->unit_size * ai->groups[i].nr_units;
 
 	/* warn if maximum distance is further than 75% of vmalloc space */
 	if (max_distance > VMALLOC_TOTAL * 3 / 4) {
-		pr_warn("max_distance=0x%zx too large for vmalloc space 0x%lx\n",
+		pr_warn("max_distance=0x%lx too large for vmalloc space 0x%lx\n",
 			max_distance, VMALLOC_TOTAL);
 #ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
 		/* and fail if we have fallback */
-- 
1.9.1