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v7.2-rc5
linux/kernel/cgroup
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Farhad Alemi b983c56426 cgroup/cpuset: rebind mm mempolicy to effective_mems, not mems_allowed 
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.

Link: https://lore.kernel.org/all/CA+0ovCiEz6SP_sn3kN4Tb+_oC=eHMXy_Ffj=usV3wREdQrUtww@mail.gmail.com/
Fixes: ae1c802382 ("cpuset: apply cs->effective_{cpus,mems}")
Closes: https://lore.kernel.org/linux-mm/CA+0ovCgxbZkXa+OU8w3s84R3KNPNxxRfmsNR-udh+afQBbGNmw@mail.gmail.com/
Suggested-by: Gregory Price <gourry@gourry.net>
Suggested-by: Waiman Long <longman@redhat.com>
Acked-by: Waiman Long <longman@redhat.com>
Signed-off-by: Farhad Alemi <farhad.alemi@berkeley.edu>
Cc: Andrew Morton <akpm@linux-foundation.org>
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>
[ david: add a comment, slightly rephrase description ]
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
2026-07-06 12:05:02 -10:00
..
cgroup-internal.h cgroup: Expose some cgroup helpers 2026-03-05 18:15:58 -10:00
cgroup-v1.c Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
cgroup.c cgroup: Changes for v7.2 2026-06-17 12:03:56 +01:00
cpuset-internal.h cgroup/cpuset: Reserve DL bandwidth only for root-domain moves 2026-05-11 10:27:14 -10:00
cpuset-v1.c cgroup: Inline cgroup_has_tasks() in cgroup.h 2026-05-15 07:24:12 -10:00
cpuset.c cgroup/cpuset: rebind mm mempolicy to effective_mems, not mems_allowed 2026-07-06 12:05:02 -10:00
debug.c Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
dmem.c cgroup/dmem: Return -ENOMEM on failed pool preallocation 2026-05-10 15:43:46 -10:00
freezer.c cgroup: cgroup.stat.local time accounting 2025-08-22 07:50:43 -10:00
legacy_freezer.c Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
Makefile kernel/cgroup: Add "dmem" memory accounting cgroup 2025-01-06 17:24:38 +01:00
misc.c Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
namespace.c treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
pids.c Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
rdma.c cgroup/rdma: Drop unnecessary READ_ONCE() on event counters 2026-05-18 09:24:50 -10:00
rstat.c cgroup: rstat: relax NMI guard after switch to try_cmpxchg 2026-05-20 09:44:35 -10:00