Re: [PATCH v3] mm/mempolicy: fix mpol_rebind_nodemask() for MPOL_F_NUMA_BALANCING

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 13 Jan 2026 09:52:42 +0800 Jinjiang Tu <tujinjiang@huawei.com> wrote:

> 
> 在 2025/12/23 19:05, Jinjiang Tu 写道:
> > commit bda420b98505 ("numa balancing: migrate on fault among multiple
> > bound nodes") adds new flag MPOL_F_NUMA_BALANCING to enable NUMA balancing
> > for MPOL_BIND memory policy.
> >
> > When the cpuset of tasks changes, the mempolicy of the task is rebound by
> > mpol_rebind_nodemask(). When MPOL_F_STATIC_NODES and MPOL_F_RELATIVE_NODES
> > are both not set, the behaviour of rebinding should be same whenever
> > MPOL_F_NUMA_BALANCING is set or not. So, when an application calls
> > set_mempolicy() with MPOL_F_NUMA_BALANCING set but both MPOL_F_STATIC_NODES
> > and MPOL_F_RELATIVE_NODES cleared, mempolicy.w.cpuset_mems_allowed should
> > be set to cpuset_current_mems_allowed nodemask. However, in current
> > implementation, mpol_store_user_nodemask() wrongly returns true, causing
> > mempolicy->w.user_nodemask to be incorrectly set to the user-specified
> > nodemask. Later, when the cpuset of the application changes,
> > mpol_rebind_nodemask() ends up rebinding based on the user-specified
> > nodemask rather than the cpuset_mems_allowed nodemask as intended.
> >
> > To fix this, only set mempolicy->w.user_nodemask to the user-specified
> > nodemask if MPOL_F_STATIC_NODES or MPOL_F_RELATIVE_NODES is present.
> >
> > Fixes: bda420b98505 ("numa balancing: migrate on fault among multiple bound nodes")
> > Reviewed-by: Gregory Price <gourry@gourry.net>
> > Reviewed-by: Huang Ying <ying.huang@linux.alibaba.com>
> > Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com>
> > ---
> > Change in v3:
> >   * update changelog
> >   * collect RB from Huang Ying
> 
> Hi, Andrew
> 
> This patch has been reviewed, could you queue this patch into mm branch?

It has been in mm.git since Dec 23 ;)

The changelog led me to believe that earlier (-stable) kernels don't
need this fix.  Maybe that was wrong?