Messages in this thread | | | Date | Mon, 21 Aug 2023 13:38:43 -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 13:32, Kui-Feng Lee wrote: > > > 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?
Oh! I missed the fact that the caller will handle it.
> >> 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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