Re: [PATCH RFC v2 1/4] mm/mempolicy: Fix get_nodes() mask miscalculation

Hi Vlastimil,

Thanks for comment!
On 2017/10/31 16:34, Vlastimil Babka wrote:

On 10/27/2017 12:14 PM, Yisheng Xie wrote:

quoted

It appears there is a nodemask miscalculation in the get_nodes()
function in mm/mempolicy.c.  This bug has two effects:

1. It is impossible to specify a length 1 nodemask.
2. It is impossible to specify a nodemask containing the last node.

This should be more specific, which syscalls are you talking about?
I assume it's set_mempolicy() and mbind() and it's the same issue that
was discussed at https://marc.info/?l=linux-mm&m=150732591909576&w=2 ?

I just missed this thread, sorry about that. Not only set_mempolicy() and
mbind(), but migrate_pages() also suffers this problem. Maybe related
manpage should documented this as your mentioned below.

Thanks
Yisheng Xie

quoted

Brent have submmit a patch before v2.6.12, however, Andi revert his
changed for ABI problem. I just resent this patch as RFC, for do not
clear about what's the problem Andi have met.

You should have CC'd Andi. As was discussed in the other thread, this
would make existing programs potentially unsafe, so we can't change it.
Instead it should be documented.

quoted

As manpage of set_mempolicy, If the value of maxnode is zero, the
nodemask argument is ignored. but we should not ignore the nodemask
when maxnode is 1.