linux-kernel - [PATCH] mm/page_alloc: Add a bulk page allocator -fix -fix

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Date:   Tue, 30 Mar 2021 12:48:47 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
        Colin Ian King <colin.king@...onical.com>
Subject: [PATCH] mm/page_alloc: Add a bulk page allocator -fix -fix

Colin Ian King reported the following problem (slightly edited)

	Author: Mel Gorman <mgorman@...hsingularity.net>
	Date:   Mon Mar 29 11:12:24 2021 +1100

	    mm/page_alloc: add a bulk page allocator

	...

	Static analysis on linux-next with Coverity has found a potential
	uninitialized variable issue in function __alloc_pages_bulk with
	the following commit:

	...

	    Uninitialized scalar variable (UNINIT)
	    15. uninit_use_in_call: Using uninitialized value alloc_flags when
	        calling prepare_alloc_pages.

	5056        if (!prepare_alloc_pages(gfp, 0, preferred_nid, nodemask,
						&ac, &alloc_gfp, &alloc_flags))

The problem is that prepare_alloc_flags only updates alloc_flags
which must have a valid initial value. The appropriate initial value is
ALLOC_WMARK_LOW to avoid the bulk allocator pushing a zone below the low
watermark without waking kswapd assuming the GFP mask allows kswapd to
be woken.

This is a second fix to the mmotm patch
mm-page_alloc-add-a-bulk-page-allocator.patch . It will cause a mild conflict
with a later patch due to renaming of an adjacent variable that is trivially
resolved. I can post a full series with the fixes merged if that is preferred.

Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
---
 mm/page_alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 92d55f80c289..dabef0b910c9 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4990,7 +4990,7 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
 	struct list_head *pcp_list;
 	struct alloc_context ac;
 	gfp_t alloc_gfp;
-	unsigned int alloc_flags;
+	unsigned int alloc_flags = ALLOC_WMARK_LOW;
 	int allocated = 0;
 
 	if (WARN_ON_ONCE(nr_pages <= 0))