Messages in this thread | | | Date | Mon, 21 Aug 2023 13:32:53 -0700 | Subject | Re: [PATCH] bpf: task_group_seq_get_next: cleanup the usage of get/put_task_struct | From | Kui-Feng Lee <> |
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On 8/21/23 13:03, Oleg Nesterov wrote: > get_pid_task() makes no sense, the code does put_task_struct() soon after. > Use find_task_by_pid_ns() instead of find_pid_ns + get_pid_task and kill > kill put_task_struct(), this allows to do get_task_struct() only once > before return. > > While at it, kill the unnecessary "if (!pid)" check in the "if (!*tid)" > block, this matches the next usage of find_pid_ns() + get_pid_task() in > this function. > > Signed-off-by: Oleg Nesterov <oleg@redhat.com> > --- > kernel/bpf/task_iter.c | 12 ++---------- > 1 file changed, 2 insertions(+), 10 deletions(-) > > diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c > index 4d1125108014..1589ec3faded 100644 > --- a/kernel/bpf/task_iter.c > +++ b/kernel/bpf/task_iter.c > @@ -42,9 +42,6 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm > if (!*tid) { > /* The first time, the iterator calls this function. */ > pid = find_pid_ns(common->pid, common->ns); > - if (!pid) > - return NULL; > - > task = get_pid_task(pid, PIDTYPE_TGID); > if (!task) > return NULL; > @@ -66,17 +63,12 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm > return task; > } > > - pid = find_pid_ns(common->pid_visiting, common->ns); > - if (!pid) > - return NULL; > - > - task = get_pid_task(pid, PIDTYPE_PID); > + task = find_task_by_pid_ns(common->pid_visiting, common->ns); > if (!task) > return NULL; > > retry: > next_task = next_thread(task); > - put_task_struct(task);
It called get_task_struct() against this task to hold a refcount at the previous time calling this function. When will it release the refcount?
> > saved_tid = *tid; > *tid = __task_pid_nr_ns(next_task, PIDTYPE_PID, common->ns); > @@ -88,7 +80,6 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm > return NULL; > } > > - get_task_struct(next_task); > common->pid_visiting = *tid; > > if (skip_if_dup_files && task->files == task->group_leader->files) { > @@ -96,6 +87,7 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm > goto retry; > } > > + get_task_struct(next_task); > return next_task; > } >
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