On 10/25/19 9:26 AM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
>
> /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@xxxxxxxxxx>
> Cc: stable
Cc: <stable@xxxxxxxxxxxxxxx>
> Fixes: 467c996c1e19 ("Print out statistics in relation to fragmentation avoidance to /proc/pagetypeinfo")
> Acked-by: Mel Gorman <mgorman@xxxxxxx>
> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> Acked-by: Waiman Long <longman@xxxxxxxxxx>
> Acked-by: Rafael Aquini <aquini@xxxxxxxxxx>
> Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> 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
>
