From: Michal Hocko mhocko@suse.com Subject: mm, vmstat: hide /proc/pagetypeinfo from normal users

/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.

Link: http://lkml.kernel.org/r/20191025072610.18526-2-mhocko@kernel.org Fixes: 467c996c1e19 ("Print out statistics in relation to fragmentation avoidance to /proc/pagetypeinfo") Signed-off-by: Michal Hocko mhocko@suse.com Reported-by: Waiman Long longman@redhat.com 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 Reviewed-by: Andrew Morton akpm@linux-foundation.org Cc: David Hildenbrand david@redhat.com Cc: Johannes Weiner hannes@cmpxchg.org Cc: Roman Gushchin guro@fb.com Cc: Konstantin Khlebnikov khlebnikov@yandex-team.ru Cc: Jann Horn jannh@google.com Cc: Song Liu songliubraving@fb.com Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/vmstat.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/vmstat.c~mm-vmstat-hide-proc-pagetypeinfo-from-normal-users +++ a/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 _