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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 890AA180003 X-Stat-Signature: 7o8px4sswwxbzsgau7i768w8rqcz8kt5 X-HE-Tag: 1783326033-629510 X-HE-Meta: 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 248O8D6D 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Farhad Alemi 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: ae1c802382f7 ("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 Suggested-by: Waiman Long Acked-by: Waiman Long Signed-off-by: Farhad Alemi Cc: Andrew Morton Cc: Alistair Popple Cc: Byungchul Park Cc: Gregory Price Cc: "Huang, Ying" Cc: Joshua Hahn Cc: Matthew Brost Cc: Rakie Kim Cc: Rasmus Villemoes Cc: Zi Yan Cc: Tejun Heo Cc: Ridong Chen Cc: Johannes Weiner Cc: "Michal Koutný" Cc: [ david: add a comment, slightly rephrase description ] Signed-off-by: David Hildenbrand (Arm) --- kernel/cgroup/cpuset.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 591e3aa487fc1..45944b3e31ca4 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -2653,7 +2653,12 @@ void cpuset_update_tasks_nodemask(struct cpuset *cs) 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 base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482 -- 2.43.0