Currently, BPF is primarily confined to cgroup2, with the exception of cgroup_iter, which supports cgroup1 fds. Unfortunately, this limitation prevents us from harnessing the full potential of BPF within cgroup1 environments. In our endeavor to seamlessly integrate BPF within our Kubernetes environment, which relies on cgroup1, we have been exploring the possibility of transitioning to cgroup2. While this transition is forward-looking, it poses challenges due to the necessity for numerous applications to adapt. While we acknowledge that cgroup2 represents the future, we also recognize that such transitions demand time and effort. As a result, we are considering an alternative approach. Instead of migrating to cgroup2, we are contemplating modifications to the BPF kernel code to ensure compatibility with cgroup1. These adjustments appear to be relatively minor, making this option more feasible. As discussed with Tejun[0], it has been determined that tying the interface directly to the cgroup1 hierarchies is acceptable. As a result, this patchset introduces cgroup1-only interfaces that operate with both hierarchy ID and cgroup ID as parameters. Within this patchset, a new cgroup1-only interface have been introduced, which is also suggested by Tejun. - [bpf_]task_get_cgroup1 Acquires the associated cgroup of a task within a specific cgroup1 hierarchy. The cgroup1 hierarchy is identified by its hierarchy ID. This new kfunc enables the tracing of tasks within a designated container or its ancestor cgroup directory in BPF programs. Additionally, it is capable of operating on named cgroups, providing valuable utility for hybrid cgroup mode scenarios. To enable the use of this new kfunc in non-sleepable contexts, we need to eliminate the reliance on the cgroup_mutex. Consequently, the cgroup root_list is made RCU-safe, allowing us to replace the cgroup_mutex with RCU read lock in specific paths. This enhancement can also bring benefits to common operations in a production environment, such as `cat /proc/self/cgroup`. As pointed out by Michal, we can further replace cgroup_mutex with the RCU read lock in other paths like cgroup_path_ns(), but it necessitates some refactoring, so I prefer to address it in a separate patchset. [0]. https://lwn.net/ml/cgroups/ZRHU6MfwqRxjBFUH@xxxxxxxxxxxxxxx/ Changes: - RFC v2 -> v3: - Use [bpf_]task_get_cgroup1 instead (Tejun) - Skip the unmounted cgroup in /proc/self/cgroup (Tejun) - Fix lockdep_is_held() in list_for_each_entry_rcu() (Tejun, oliver.sang@xxxxxxxxx) - Drop the warning in __cset_cgroup_from_root()(Tejun) - Fix mismatched comments (Tejun, lkp@xxxxxxxxx) - Add a explicit warning in current_cgns_cgroup_from_root (Michal) - RFC v1 -> RFC v2: - Introduce a new kunc to get cgroup kptr instead of getting the cgrp ID (Tejun) - Eliminate the cgroup_mutex by making cgroup root_list RCU-safe, as disccussed with Michal - RFC v1: bpf, cgroup: Add BPF support for cgroup1 hierarchy https://lwn.net/Articles/947130/ - bpf, cgroup: Add bpf support for cgroup controller https://lwn.net/Articles/945318/ - bpf, cgroup: Enable cgroup_array map on cgroup1 https://lore.kernel.org/bpf/20230903142800.3870-1-laoar.shao@xxxxxxxxx Yafang Shao (11): cgroup: Remove unnecessary list_empty() cgroup: Make operations on the cgroup root_list RCU safe cgroup: Eliminate the need for cgroup_mutex in proc_cgroup_show() cgroup: Add annotation for holding namespace_sem in current_cgns_cgroup_from_root() cgroup: Add a new helper for cgroup1 hierarchy bpf: Add a new kfunc for cgroup1 hierarchy selftests/bpf: Fix issues in setup_classid_environment() selftests/bpf: Add parallel support for classid selftests/bpf: Add a new cgroup helper get_classid_cgroup_id() selftests/bpf: Add a new cgroup helper get_cgroup_hierarchy_id() selftests/bpf: Add selftests for cgroup1 hierarchy include/linux/cgroup-defs.h | 1 + include/linux/cgroup.h | 4 +- kernel/bpf/helpers.c | 20 +++ kernel/cgroup/cgroup-internal.h | 4 +- kernel/cgroup/cgroup-v1.c | 33 +++++ kernel/cgroup/cgroup.c | 45 ++++-- tools/testing/selftests/bpf/cgroup_helpers.c | 113 ++++++++++++--- tools/testing/selftests/bpf/cgroup_helpers.h | 4 +- .../selftests/bpf/prog_tests/cgroup1_hierarchy.c | 159 +++++++++++++++++++++ .../testing/selftests/bpf/prog_tests/cgroup_v1v2.c | 2 +- .../selftests/bpf/progs/test_cgroup1_hierarchy.c | 72 ++++++++++ 11 files changed, 420 insertions(+), 37 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/cgroup1_hierarchy.c create mode 100644 tools/testing/selftests/bpf/progs/test_cgroup1_hierarchy.c -- 1.8.3.1
