linux-kernel - [PATCH] mm/page_alloc.c: Use div64_ul instead of do

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Date:   Fri,  7 Jan 2022 02:17:51 +0000
From:   cgel.zte@...il.com
To:     akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Changcheng Deng <deng.changcheng@....com.cn>,
        Zeal Robot <zealci@....com.cn>
Subject: [PATCH] mm/page_alloc.c: Use div64_ul instead of do_div

From: Changcheng Deng <deng.changcheng@....com.cn>

do_div() does a 64-by-32 division. Here the divisor is an unsigned long
which on some platforms is 64 bit wide. So use div64_ul instead of do_div
to avoid a possible truncation.

Reported-by: Zeal Robot <zealci@....com.cn>
Signed-off-by: Changcheng Deng <deng.changcheng@....com.cn>
---
 mm/page_alloc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8dd6399bafb5..60469b616ac1 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8431,7 +8431,7 @@ static void __setup_per_zone_wmarks(void)
 
 		spin_lock_irqsave(&zone->lock, flags);
 		tmp = (u64)pages_min * zone_managed_pages(zone);
-		do_div(tmp, lowmem_pages);
+		tmp = div64_ul(tmp, lowmem_pages);
 		if (is_highmem(zone)) {
 			/*
 			 * __GFP_HIGH and PF_MEMALLOC allocations usually don't
@@ -8804,7 +8804,7 @@ void *__init alloc_large_system_hash(const char *tablename,
 	/* limit allocation size to 1/16 total memory by default */
 	if (max == 0) {
 		max = ((unsigned long long)nr_all_pages << PAGE_SHIFT) >> 4;
-		do_div(max, bucketsize);
+		max = div64_ul(max, bucketsize);
 	}
 	max = min(max, 0x80000000ULL);
 
-- 
2.25.1