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

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

[Jinjiang Tu]

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

 include/uapi/linux/mempolicy.h | 3 +++
 mm/mempolicy.c                 | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/mempolicy.h b/include/uapi/linux/mempolicy.h
index 8fbbe613611a..6c962d866e86 100644
--- a/include/uapi/linux/mempolicy.h
+++ b/include/uapi/linux/mempolicy.h
@@ -39,6 +39,9 @@ enum {
 #define MPOL_MODE_FLAGS							\
 	(MPOL_F_STATIC_NODES | MPOL_F_RELATIVE_NODES | MPOL_F_NUMA_BALANCING)
 
+/* Whether the nodemask is specified by users */
+#define MPOL_USER_NODEMASK_FLAGS (MPOL_F_STATIC_NODES | MPOL_F_RELATIVE_NODES)
+
 /* Flags for get_mempolicy */
 #define MPOL_F_NODE	(1<<0)	/* return next IL mode instead of node mask */
 #define MPOL_F_ADDR	(1<<1)	/* look up vma using address */
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 68a98ba57882..76da50425712 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -365,7 +365,7 @@ static const struct mempolicy_operations {
 
 static inline int mpol_store_user_nodemask(const struct mempolicy *pol)
 {
-	return pol->flags & MPOL_MODE_FLAGS;
+	return pol->flags & MPOL_USER_NODEMASK_FLAGS;
 }
 
 static void mpol_relative_nodemask(nodemask_t *ret, const nodemask_t *orig,
-- 
2.43.0

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

[Jinjiang Tu]

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?

>   include/uapi/linux/mempolicy.h | 3 +++
>   mm/mempolicy.c                 | 2 +-
>   2 files changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/mempolicy.h b/include/uapi/linux/mempolicy.h
> index 8fbbe613611a..6c962d866e86 100644
> --- a/include/uapi/linux/mempolicy.h
> +++ b/include/uapi/linux/mempolicy.h
> @@ -39,6 +39,9 @@ enum {
>   #define MPOL_MODE_FLAGS							\
>   	(MPOL_F_STATIC_NODES | MPOL_F_RELATIVE_NODES | MPOL_F_NUMA_BALANCING)
>   
> +/* Whether the nodemask is specified by users */
> +#define MPOL_USER_NODEMASK_FLAGS (MPOL_F_STATIC_NODES | MPOL_F_RELATIVE_NODES)
> +
>   /* Flags for get_mempolicy */
>   #define MPOL_F_NODE	(1<<0)	/* return next IL mode instead of node mask */
>   #define MPOL_F_ADDR	(1<<1)	/* look up vma using address */
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 68a98ba57882..76da50425712 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -365,7 +365,7 @@ static const struct mempolicy_operations {
>   
>   static inline int mpol_store_user_nodemask(const struct mempolicy *pol)
>   {
> -	return pol->flags & MPOL_MODE_FLAGS;
> +	return pol->flags & MPOL_USER_NODEMASK_FLAGS;
>   }
>   
>   static void mpol_relative_nodemask(nodemask_t *ret, const nodemask_t *orig,

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

[Andrew Morton]

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?

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

[Jinjiang Tu]

在 2026/1/14 8:37, Andrew Morton 写道:
> 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 ;)

Indeed, I missed the email. Thanks.

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

Yes. This only fixes a minor issue.

>