Re: [PATCH bpf-next v7 1/5] bpf: Parameterize task iterators.

[Kui-Feng Lee <kuifeng@fb.com>]

On Fri, 2022-08-26 at 12:30 -0700, Yonghong Song wrote:
> 
> 
> On 8/25/22 5:37 PM, Kui-Feng Lee wrote:
> > Allow creating an iterator that loops through resources of one
> > thread/process.
> > 
> > People could only create iterators to loop through all resources of
> > files, vma, and tasks in the system, even though they were
> > interested
> > in only the resources of a specific task or process.  Passing the
> > additional parameters, people can now create an iterator to go
> > through all resources or only the resources of a task.
> > 
> > Signed-off-by: Kui-Feng Lee <kuifeng@fb.com>
> > Acked-by: Yonghong Song <yhs@fb.com>
> > ---
> >   include/linux/bpf.h            |  25 +++++++
> >   include/uapi/linux/bpf.h       |   6 ++
> >   kernel/bpf/task_iter.c         | 128 ++++++++++++++++++++++++++--
> > -----
> >   tools/include/uapi/linux/bpf.h |   6 ++
> >   4 files changed, 141 insertions(+), 24 deletions(-)
> > 
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index 9c1674973e03..31ac2c1181f5 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -1730,6 +1730,27 @@ int bpf_obj_get_user(const char __user
> > *pathname, int flags);
> >         extern int bpf_iter_ ## target(args);                   \
> >         int __init bpf_iter_ ## target(args) { return 0; }
> >   
> > +/*
> > + * The task type of iterators.
> > + *
> > + * For BPF task iterators, they can be parameterized with various
> > + * parameters to visit only some of tasks.
> > + *
> > + * BPF_TASK_ITER_ALL (default)
> > + *     Iterate over resources of every task.
> > + *
> > + * BPF_TASK_ITER_TID
> > + *     Iterate over resources of a task/tid.
> > + *
> > + * BPF_TASK_ITER_TGID
> > + *     Iterate over resources of every task of a process / task
> > group.
> > + */
> > +enum bpf_iter_task_type {
> > +       BPF_TASK_ITER_ALL = 0,
> > +       BPF_TASK_ITER_TID,
> > +       BPF_TASK_ITER_TGID,
> > +};
> > +
> >   struct bpf_iter_aux_info {
> >         /* for map_elem iter */
> >         struct bpf_map *map;
> > @@ -1739,6 +1760,10 @@ struct bpf_iter_aux_info {
> >                 struct cgroup *start; /* starting cgroup */
> >                 enum bpf_cgroup_iter_order order;
> >         } cgroup;
> > +       struct {
> > +               enum bpf_iter_task_type type;
> > +               u32 pid;
> > +       } task;
> >   };
> >   
> >   typedef int (*bpf_iter_attach_target_t)(struct bpf_prog *prog,
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index 0f61f09f467a..385deab984e1 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -110,6 +110,12 @@ union bpf_iter_link_info {
> >                 __u32   cgroup_fd;
> >                 __u64   cgroup_id;
> >         } cgroup;
> > +       /* Parameters of task iterators. */
> > +       struct {
> > +               __u32   tid;
> > +               __u32   pid;
> > +               __u32   pid_fd;
> > +       } task;
> >   };
> >   
> >   /* BPF syscall commands, see bpf(2) man-page for more details. */
> > diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
> > index 8c921799def4..1200cfde71e3 100644
> > --- a/kernel/bpf/task_iter.c
> > +++ b/kernel/bpf/task_iter.c
> > @@ -12,6 +12,8 @@
> >   
> >   struct bpf_iter_seq_task_common {
> >         struct pid_namespace *ns;
> > +       enum bpf_iter_task_type type;
> > +       u32 pid;
> >   };
> >   
> >   struct bpf_iter_seq_task_info {
> > @@ -22,24 +24,54 @@ struct bpf_iter_seq_task_info {
> >         u32 tid;
> >   };
> >   
> > -static struct task_struct *task_seq_get_next(struct pid_namespace
> > *ns,
> > +static bool matched_task(struct task_struct *task,
> > +                        struct bpf_iter_seq_task_common *common,
> > +                        bool skip_if_dup_file)
> > +{
> > +       /* Should not have the same 'files' if skip_if_dup_file is
> > true */
> > +       bool diff_files_if =
> > +               !skip_if_dup_file ||
> > +               (thread_group_leader(task) &&
> > +                task->files != task->group_leader->files);
> 
> Should this be
>         !skip_if_dup_file || thread_group_leader(task) ||
>         task->files != task->group_leader->files
> ?

Good catch!
This change will be rollbacked by using next_thread().

> 
> > +       /* Should have the given tgid if the type is
> > BPF_TASK_ITER_TGI */
> 
> BPF_TASK_ITER_TGID?
> 
> > +       bool have_tgid_if =
> > +               common->type != BPF_TASK_ITER_TGID ||
> > +               __task_pid_nr_ns(task, PIDTYPE_TGID,
> > +                                common->ns) == common->pid;
> > +       return diff_files_if && have_tgid_if;
> > +}
> > +
> > +
> > +static struct task_struct *task_seq_get_next(struct
> > bpf_iter_seq_task_common *common,
> >                                              u32 *tid,
> >                                              bool
> > skip_if_dup_files)
> >   {
> >         struct task_struct *task = NULL;
> >         struct pid *pid;
> >   
> > +       if (common->type == BPF_TASK_ITER_TID) {
> > +               if (*tid && *tid != common->pid)
> > +                       return NULL;
> > +               rcu_read_lock();
> > +               pid = find_pid_ns(common->pid, common->ns);
> > +               if (pid) {
> > +                       task = get_pid_task(pid, PIDTYPE_PID);
> > +                       *tid = common->pid;
> > +               }
> > +               rcu_read_unlock();
> > +               return task;
> > +       }
> > +
> >         rcu_read_lock();
> >   retry:
> > -       pid = find_ge_pid(*tid, ns);
> > +       pid = find_ge_pid(*tid, common->ns);
> >         if (pid) {
> > -               *tid = pid_nr_ns(pid, ns);
> > +               *tid = pid_nr_ns(pid, common->ns);
> >                 task = get_pid_task(pid, PIDTYPE_PID);
> >                 if (!task) {
> >                         ++*tid;
> >                         goto retry;
> > -               } else if (skip_if_dup_files &&
> > !thread_group_leader(task) &&
> > -                          task->files == task->group_leader-
> > >files) {
> > +               } else if (!matched_task(task, common,
> > skip_if_dup_files)) {
> >                         put_task_struct(task);
> >                         task = NULL;
> >                         ++*tid;
> > @@ -56,7 +88,7 @@ static void *task_seq_start(struct seq_file *seq,
> > loff_t *pos)
> >         struct bpf_iter_seq_task_info *info = seq->private;
> >         struct task_struct *task;
> >   
> > -       task = task_seq_get_next(info->common.ns, &info->tid,
> > false);
> > +       task = task_seq_get_next(&info->common, &info->tid, false);
> >         if (!task)
> >                 return NULL;
> >   
> [...]