On 10/25/19 9:26 AM, Michal Hocko wrote:

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

Cc: stable@vger.kernel.org

Fixes: 467c996c1e19 ("Print out statistics in relation to fragmentation avoidance to /proc/pagetypeinfo") Acked-by: Mel Gorman mgorman@suse.de Acked-by: Vlastimil Babka vbabka@suse.cz Acked-by: Waiman Long longman@redhat.com Acked-by: Rafael Aquini aquini@redhat.com Acked-by: David Rientjes rientjes@google.com 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