* + cgroup-cpuset-rebind-mm-mempolicy-to-effective_mems-not-mems_allowed.patch added to mm-hotfixes-unstable branch
@ 2026-06-28 6:15 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2026-06-28 6:15 UTC (permalink / raw)
To: mm-commits, ziy, ying.huang, tj, stable, rakie.kim, matthew.brost,
longman, linux, joshua.hahnjy, gourry, david, byungchul, apopple,
farhad.alemi, akpm
The patch titled
Subject: cgroup/cpuset: rebind mm mempolicy to effective_mems, not mems_allowed
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
cgroup-cpuset-rebind-mm-mempolicy-to-effective_mems-not-mems_allowed.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/cgroup-cpuset-rebind-mm-mempolicy-to-effective_mems-not-mems_allowed.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days
------------------------------------------------------
From: Farhad Alemi <farhad.alemi@berkeley.edu>
Subject: cgroup/cpuset: rebind mm mempolicy to effective_mems, not mems_allowed
Date: Sun, 14 Jun 2026 06:25:55 -0700
Creating a child cpuset where cpuset.mems is never set leads to a div/0
when a VMA mempolicy with MPOL_F_RELATIVE_NODES rebinds in response to a
CPU hotplug event.
Reproduction steps:
1) Create a cgroup w/ cpuset controls (do not set cpuset.mems)
2) Move the task into the child cpuset
3) Create a VMA mempolicy for that task with MPOL_F_RELATIVE_NODES
4) unplug and hotplug a cpu
echo 0 > /sys/devices/system/cpu/cpu1/online
echo 1 > /sys/devices/system/cpu/cpu1/online
5) mempolicy rebind does a div/0 in mpol_relative_nodemask on the
call to __nodes_fold()
The cpuset code passes (cs->mems_allowed) which is not guaranteed to have
nodes to the rebind routine. Use cs->effective_mems instead, which is
guaranteed to have a non-empty nodemask.
Link: https://lore.kernel.org/linux-mm/CA+0ovCgxbZkXa+OU8w3s84R3KNPNxxRfmsNR-udh+afQBbGNmw@mail.gmail.com/
Link: https://lore.kernel.org/all/CA+0ovCiEz6SP_sn3kN4Tb+_oC=eHMXy_Ffj=usV3wREdQrUtww@mail.gmail.com/
Link: https://lore.kernel.org/CA+0ovCgfHJHv5d1mzapWWvF-LhjppzDX8NPPLvCPZxPKg8RiYw@mail.gmail.com
Fixes: ae1c802382f7 ("cpuset: apply cs->effective_{cpus,mems}")
Signed-off-by: Farhad Alemi <farhad.alemi@berkeley.edu>
Suggested-by: Gregory Price <gourry@gourry.net>
Suggested-by: Waiman Long <longman@redhat.com>
Closes: https://lore.kernel.org/linux-mm/CA+0ovCgxbZkXa+OU8w3s84R3KNPNxxRfmsNR-udh+afQBbGNmw@mail.gmail.com/
Acked-by: Waiman Long <longman@redhat.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Gregory Price <gourry@gourry.net>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
kernel/cgroup/cpuset.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/cgroup/cpuset.c~cgroup-cpuset-rebind-mm-mempolicy-to-effective_mems-not-mems_allowed
+++ a/kernel/cgroup/cpuset.c
@@ -2653,7 +2653,7 @@ void cpuset_update_tasks_nodemask(struct
migrate = is_memory_migrate(cs);
- mpol_rebind_mm(mm, &cs->mems_allowed);
+ mpol_rebind_mm(mm, &cs->effective_mems);
if (migrate)
cpuset_migrate_mm(mm, &cs->old_mems_allowed, &newmems);
else
_
Patches currently in -mm which might be from farhad.alemi@berkeley.edu are
cgroup-cpuset-rebind-mm-mempolicy-to-effective_mems-not-mems_allowed.patch
^ permalink raw reply [flat|nested] 2+ messages in thread
* + cgroup-cpuset-rebind-mm-mempolicy-to-effective_mems-not-mems_allowed.patch added to mm-hotfixes-unstable branch
@ 2026-07-06 22:35 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2026-07-06 22:35 UTC (permalink / raw)
To: mm-commits, ziy, ying.huang, tj, stable, ridong.chen, rakie.kim,
mkoutny, matthew.brost, longman, linux, joshua.hahnjy, hannes,
gourry, david, byungchul, apopple, farhad.alemi, akpm
[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 4198 bytes --]
The patch titled
Subject: cgroup/cpuset: rebind mm mempolicy to effective_mems, not mems_allowed
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
cgroup-cpuset-rebind-mm-mempolicy-to-effective_mems-not-mems_allowed.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/cgroup-cpuset-rebind-mm-mempolicy-to-effective_mems-not-mems_allowed.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days
------------------------------------------------------
From: Farhad Alemi <farhad.alemi@berkeley.edu>
Subject: cgroup/cpuset: rebind mm mempolicy to effective_mems, not mems_allowed
Date: Mon, 6 Jul 2026 10:20:23 +0200
Creating a child cpuset where cpuset.mems is never set leads to a div/0
when a VMA mempolicy with MPOL_F_RELATIVE_NODES rebinds in response to a
CPU hotplug event.
Reproduction steps:
1) Create a cgroup w/ cpuset controls (do not set cpuset.mems)
2) Move the task into the child cpuset
3) Create a VMA mempolicy for that task with MPOL_F_RELATIVE_NODES
4) unplug and hotplug a cpu
echo 0 > /sys/devices/system/cpu/cpu1/online
echo 1 > /sys/devices/system/cpu/cpu1/online
5) mempolicy rebind does a div/0 in mpol_relative_nodemask on the
call to __nodes_fold()
The cpuset code passes (cs->mems_allowed) which is not guaranteed to have
nodes to the rebind routine. Use cs->effective_mems instead, which is
guaranteed to have a non-empty nodemask once we reach that code path.
[david@kernel.org: add a comment, slightly rephrase description]
Link: https://lore.kernel.org/all/CA+0ovCiEz6SP_sn3kN4Tb+_oC=eHMXy_Ffj=usV3wREdQrUtww@mail.gmail.com/
Link: https://lore.kernel.org/20260706082023.60832-1-david@kernel.org
Signed-off-by: Farhad Alemi <farhad.alemi@berkeley.edu>
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
Suggested-by: Gregory Price <gourry@gourry.net>
Suggested-by: Waiman Long <longman@redhat.com>
Acked-by: Waiman Long <longman@redhat.com>
Fixes: ae1c802382f7 ("cpuset: apply cs->effective_{cpus,mems}")
Closes: https://lore.kernel.org/linux-mm/CA+0ovCgxbZkXa+OU8w3s84R3KNPNxxRfmsNR-udh+afQBbGNmw@mail.gmail.com/
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Ridong Chen <ridong.chen@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Michal Koutný" <mkoutny@suse.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
kernel/cgroup/cpuset.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
--- a/kernel/cgroup/cpuset.c~cgroup-cpuset-rebind-mm-mempolicy-to-effective_mems-not-mems_allowed
+++ a/kernel/cgroup/cpuset.c
@@ -2653,7 +2653,12 @@ void cpuset_update_tasks_nodemask(struct
migrate = is_memory_migrate(cs);
- mpol_rebind_mm(mm, &cs->mems_allowed);
+ /*
+ * For v1 we can have empty effective_mems, but we cannot
+ * attach any tasks (see cpuset_can_attach_check()). For v2,
+ * effective_mems is guaranteed to not be empty.
+ */
+ mpol_rebind_mm(mm, &cs->effective_mems);
if (migrate)
cpuset_migrate_mm(mm, &cs->old_mems_allowed, &newmems);
else
_
Patches currently in -mm which might be from farhad.alemi@berkeley.edu are
cgroup-cpuset-rebind-mm-mempolicy-to-effective_mems-not-mems_allowed.patch
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