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From:   Michal Hocko <mhocko@kernel.org>
To:     Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>, Waiman Long <longman@redhat.com>
Cc:     Johannes Weiner <hannes@cmpxchg.org>, Roman Gushchin <guro@fb.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
        Jann Horn <jannh@google.com>, Song Liu <songliubraving@fb.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Rafael Aquini <aquini@redhat.com>, <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Michal Hocko <mhocko@suse.com>
Subject: [RFC PATCH 1/2] mm, vmstat: hide /proc/pagetypeinfo from normal users
Date:   Wed, 23 Oct 2019 12:27:36 +0200
Message-Id: <20191023102737.32274-2-mhocko@kernel.org>
In-Reply-To: <20191023102737.32274-1-mhocko@kernel.org>
References: <20191023095607.GE3016@techsingularity.net>
 <20191023102737.32274-1-mhocko@kernel.org>
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From: Michal Hocko <mhocko@suse.com>

/proc/pagetypeinfo is a debugging tool to examine internal page
allocator state wrt to fragmentation. It is not very useful for
any other use so normal users really do not need to read this file.

Waiman Long has noticed that reading this file can have negative side
effects because zone->lock is necessary for gathering data and that
a) interferes with the page allocator and its users and b) can lead to
hard lockups on large machines which have very long free_list.

Reduce both issues by simply not exporting the file to regular users.

Reported-by: Waiman Long <longman@redhat.com>
Cc: stable
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 mm/vmstat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 6afc892a148a..4e885ecd44d1 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1972,7 +1972,7 @@ void __init init_mm_internals(void)
 #endif
 #ifdef CONFIG_PROC_FS
 	proc_create_seq("buddyinfo", 0444, NULL, &fragmentation_op);
-	proc_create_seq("pagetypeinfo", 0444, NULL, &pagetypeinfo_op);
+	proc_create_seq("pagetypeinfo", 0400, NULL, &pagetypeinfo_op);
 	proc_create_seq("vmstat", 0444, NULL, &vmstat_op);
 	proc_create_seq("zoneinfo", 0444, NULL, &zoneinfo_op);
 #endif
-- 
2.20.1