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Farhad Alemi
b983c56426
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 <[email protected]>
Suggested-by: Waiman Long <[email protected]>
Acked-by: Waiman Long <[email protected]>
Signed-off-by: Farhad Alemi <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Byungchul Park <[email protected]>
Cc: Gregory Price <[email protected]>
Cc: "Huang, Ying" <[email protected]>
Cc: Joshua Hahn <[email protected]>
Cc: Matthew Brost <[email protected]>
Cc: Rakie Kim <[email protected]>
Cc: Rasmus Villemoes <[email protected]>
Cc: Zi Yan <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Ridong Chen <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: "Michal Koutný" <[email protected]>
Cc: <[email protected]>
[ david: add a comment, slightly rephrase description ]
Signed-off-by: David Hildenbrand (Arm) <[email protected]>
Signed-off-by: Tejun Heo <[email protected]>