From: Andrii Nakryiko <andriin@fb.com>
Date: Wed, 13 May 2020 22:51:37 -0700
Subject: bpf: Fix bpf_iter's task iterator logic
Patch-mainline: v5.8-rc1
Git-commit: c70f34a8ac66c2cb05593ef5760142e5f862a9b4
References: bsc#1177028
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.
Fixes: eaaacd23910f ("bpf: Add task and task/file iterator targets")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200514055137.1564581-1-andriin@fb.com
Acked-by: Gary Lin <glin@suse.com>
---
kernel/bpf/task_iter.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -27,9 +27,15 @@ static struct task_struct *task_seq_get_
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;