task_seq_get_next might stop prematurely if get_pid_task() fails to get
task_struct. Failure to do so doesn't mean that there are no more tasks with
higher pids. Procfs's iteration algorithm (see next_tgid in fs/proc/base.c)
does a retry in such case. After this fix, instead of stopping prematurely
after about 300 tasks on my server, bpf_iter program now returns >4000, which
sounds much closer to reality.
Cc: Yonghong Song <yhs@xxxxxx>
Fixes: eaaacd23910f ("bpf: Add task and task/file iterator targets")
Acked-by: Yonghong Song <yhs@xxxxxx>
Signed-off-by: Andrii Nakryiko <andriin@xxxxxx>
---
kernel/bpf/task_iter.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index a9b7264dda08..4dbf2b6035f8 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -27,9 +27,15 @@ static struct task_struct *task_seq_get_next(struct pid_namespace *ns,
struct pid *pid;
rcu_read_lock();
+retry:
pid = idr_get_next(&ns->idr, tid);
- if (pid)
+ if (pid) {
task = get_pid_task(pid, PIDTYPE_PID);
+ if (!task) {
+ ++*tid;
+ goto retry;
+ }
+ }
rcu_read_unlock();
return task;
--
2.24.1
