On Thu, Nov 25, 2021 at 02:09:00PM +0800, Yafang Shao wrote:
>
>
> > On Sep 17, 2021, at 12:24 AM, Roman Gushchin <guro@xxxxxx> wrote:
> >
> > This patch adds 3 helpers useful for dealing with sched entities:
> > u64 bpf_sched_entity_to_tgidpid(struct sched_entity *se);
> > u64 bpf_sched_entity_to_cgrpid(struct sched_entity *se);
> > long bpf_sched_entity_belongs_to_cgrp(struct sched_entity *se, u64 cgrpid);
> >
> > Sched entity is a basic structure used by the scheduler to represent
> > schedulable objects: tasks and cgroups (if CONFIG_FAIR_GROUP_SCHED
> > is enabled). It will be passed as an argument to many bpf hooks, so
> > scheduler bpf programs need a convenient way to deal with it.
> >
> > bpf_sched_entity_to_tgidpid() and bpf_sched_entity_to_cgrpid() are
> > useful to identify a sched entity in userspace terms (pid, tgid and
> > cgroup id). bpf_sched_entity_belongs_to_cgrp() allows to check whether
> > a sched entity belongs to sub-tree of a cgroup. It allows to write
> > cgroup-specific scheduler policies even without enabling the cgroup
> > cpu controller.
> >
> > Signed-off-by: Roman Gushchin <guro@xxxxxx>
> > ---
> > include/uapi/linux/bpf.h | 23 +++++++++++
> > kernel/sched/bpf_sched.c | 74 ++++++++++++++++++++++++++++++++++
> > scripts/bpf_doc.py | 2 +
> > tools/include/uapi/linux/bpf.h | 23 +++++++++++
> > 4 files changed, 122 insertions(+)
> >
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index 6dfbebb8fc8f..199e4a92820d 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -4900,6 +4900,26 @@ union bpf_attr {
> > * **-EINVAL** if *flags* is not zero.
> > *
> > * **-ENOENT** if architecture does not support branch records.
> > + *
> > + * u64 bpf_sched_entity_to_tgidpid(struct sched_entity *se)
> > + * Description
> > + * Return task's encoded tgid and pid if the sched entity is a task.
> > + * Return
> > + * Tgid and pid encoded as tgid << 32 \| pid, if *se* is a task. (u64)-1 otherwise.
> > + *
> > + * u64 bpf_sched_entity_to_cgrpid(struct sched_entity *se)
> > + * Description
> > + * Return cgroup id if the given sched entity is a cgroup.
> > + * Return
> > + * Cgroup id, if *se* is a cgroup. (u64)-1 otherwise.
> > + *
> > + * long bpf_sched_entity_belongs_to_cgrp(struct sched_entity *se, u64 cgrpid)
> > + * Description
> > + * Checks whether the sched entity belongs to a cgroup or
> > + * it's sub-tree. It doesn't require a cgroup CPU controller
> > + * to be enabled.
> > + * Return
> > + * 1 if the sched entity belongs to a cgroup, 0 otherwise.
> > */
> > #define __BPF_FUNC_MAPPER(FN) \
> > FN(unspec), \
> > @@ -5079,6 +5099,9 @@ union bpf_attr {
> > FN(get_attach_cookie), \
> > FN(task_pt_regs), \
> > FN(get_branch_snapshot), \
> > + FN(sched_entity_to_tgidpid), \
> > + FN(sched_entity_to_cgrpid), \
> > + FN(sched_entity_belongs_to_cgrp), \
> > /* */
> >
> > /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> > diff --git a/kernel/sched/bpf_sched.c b/kernel/sched/bpf_sched.c
> > index 2f05c186cfd0..ead691dc6e85 100644
> > --- a/kernel/sched/bpf_sched.c
> > +++ b/kernel/sched/bpf_sched.c
> > @@ -42,12 +42,86 @@ int bpf_sched_verify_prog(struct bpf_verifier_log *vlog,
> > return 0;
> > }
> >
> > +BPF_CALL_1(bpf_sched_entity_to_tgidpid, struct sched_entity *, se)
> > +{
> > + if (entity_is_task(se)) {
> > + struct task_struct *task = task_of(se);
> > +
> > + return (u64) task->tgid << 32 | task->pid;
> > + } else {
> > + return (u64) -1;
> > + }
> > +}
> > +
> > +BPF_CALL_1(bpf_sched_entity_to_cgrpid, struct sched_entity *, se)
> > +{
> > +#ifdef CONFIG_FAIR_GROUP_SCHED
> > + if (!entity_is_task(se))
> > + return cgroup_id(se->cfs_rq->tg->css.cgroup);
> > +#endif
> > + return (u64) -1;
> > +}
> > +
> > +BPF_CALL_2(bpf_sched_entity_belongs_to_cgrp, struct sched_entity *, se,
> > + u64, cgrpid)
> > +{
> > +#ifdef CONFIG_CGROUPS
> > + struct cgroup *cgrp;
> > + int level;
> > +
> > + if (entity_is_task(se))
> > + cgrp = task_dfl_cgroup(task_of(se));
> > +#ifdef CONFIG_FAIR_GROUP_SCHED
> > + else
> > + cgrp = se->cfs_rq->tg->css.cgroup;
>
> It is incorrect.
> It should use se->my_q->tg->css.cgroup and some possible NULL check. (for autogroup)
> se->cfs_rq and se->my_q are different. se->my_q is the cfs_rq of this se itself, while the se->cfs_rq may be the parent.
Indeed. Thanks, will fix in the next version.
