[PATCH 3/3 v4 bpf-next] bpf: optimize task iteration

[Jonathan Lemon]

From: Jonathan Lemon <b...@fb.com>

Only obtain the task reference count at the end of the RCU section
instead of repeatedly obtaining/releasing it when iterating though
a thread group.

Jump to the correct branch when it is known that the task is NULL.

Signed-off-by: Jonathan Lemon <jonathan.le...@gmail.com>
---
 kernel/bpf/task_iter.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index dc4007f1843b..598a8d7da5bf 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -33,7 +33,7 @@ static struct task_struct *task_seq_get_next(struct 
pid_namespace *ns,
        pid = find_ge_pid(*tid, ns);
        if (pid) {
                *tid = pid_nr_ns(pid, ns);
-               task = get_pid_task(pid, PIDTYPE_PID);
+               task = pid_task(pid, PIDTYPE_PID);
                if (!task) {
                        ++*tid;
                        goto retry;
@@ -44,6 +44,7 @@ static struct task_struct *task_seq_get_next(struct 
pid_namespace *ns,
                        ++*tid;
                        goto retry;
                }
+               get_task_struct(task);
        }
        rcu_read_unlock();
 
@@ -148,12 +149,12 @@ task_file_seq_get_next(struct bpf_iter_seq_task_file_info 
*info)
         * it held a reference to the task/files_struct/file.
         * Otherwise, it does not hold any reference.
         */
-again:
        if (info->task) {
                curr_task = info->task;
                curr_files = info->files;
                curr_fd = info->fd;
        } else {
+again:
                curr_task = task_seq_get_next(ns, &curr_tid, true);
                if (!curr_task) {
                        info->task = NULL;
-- 
2.24.1