mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2026-03-03 18:28:01 +01:00
3d702678f5
commitbda420b985("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. I can reproduce with the following steps in qemu with 4 NUMA nodes: 1. echo '+cpuset' > /sys/fs/cgroup/cgroup.subtree_control 2. mkdir /sys/fs/cgroup/test 3. ./reproducer & 4. cat /proc/$pid/numa_maps, the task is bound to NUMA 1 5. echo $pid > /sys/fs/cgroup/test/cgroup.procs 6. cat /proc/$pid/numa_maps, the task is bound to NUMA 0 now. The reproducer code: int main() { struct bitmask *bmp; int ret; bmp = numa_parse_nodestring("1"); ret = set_mempolicy(MPOL_BIND | MPOL_F_NUMA_BALANCING, bmp->maskp, bmp->size + 1); if (ret < 0) { perror("Failed to call set_mempolicy"); exit(-1); } while (1); return 0; } If I call set_mempolicy() without MPOL_F_NUMA_BALANCING in the reproducer code. After step 5, the task is still bound to NUMA 1. 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. Link: https://lkml.kernel.org/r/20260120011018.1256654-1-tujinjiang@huawei.com Link: https://lkml.kernel.org/r/20251223110523.1161421-1-tujinjiang@huawei.com Fixes:bda420b985("numa balancing: migrate on fault among multiple bound nodes") Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com> Reviewed-by: Gregory Price <gourry@gourry.net> Reviewed-by: Huang Ying <ying.huang@linux.alibaba.com> Acked-by: David Hildenbrand (Red Hat) <david@kernel.org> Cc: Alistair Popple <apopple@nvidia.com> Cc: Byungchul Park <byungchul@sk.com> Cc: Joshua Hahn <joshua.hahnjy@gmail.com> Cc: Kefeng Wang <wangkefeng.wang@huawei.com> Cc: Mathew Brost <matthew.brost@intel.com> Cc: Mel Gorman <mgorman <mgorman@suse.de> Cc: Rakie Kim <rakie.kim@sk.com> Cc: Zi Yan <ziy@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>