* [PATCH v2 bpf-next] bpf: fix bpf_iter's task iterator logic
@ 2020-05-14 5:51 Andrii Nakryiko
2020-05-15 1:38 ` Alexei Starovoitov
0 siblings, 1 reply; 2+ messages in thread
From: Andrii Nakryiko @ 2020-05-14 5:51 UTC (permalink / raw)
To: bpf, netdev, ast, daniel
Cc: andrii.nakryiko, kernel-team, Andrii Nakryiko, Yonghong Song
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@fb.com>
Fixes: eaaacd23910f ("bpf: Add task and task/file iterator targets")
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
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
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v2 bpf-next] bpf: fix bpf_iter's task iterator logic
2020-05-14 5:51 [PATCH v2 bpf-next] bpf: fix bpf_iter's task iterator logic Andrii Nakryiko
@ 2020-05-15 1:38 ` Alexei Starovoitov
0 siblings, 0 replies; 2+ messages in thread
From: Alexei Starovoitov @ 2020-05-15 1:38 UTC (permalink / raw)
To: Andrii Nakryiko
Cc: bpf, Network Development, Alexei Starovoitov, Daniel Borkmann,
Andrii Nakryiko, Kernel Team, Yonghong Song
On Wed, May 13, 2020 at 10:54 PM Andrii Nakryiko <andriin@fb.com> wrote:
>
> 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@fb.com>
> Fixes: eaaacd23910f ("bpf: Add task and task/file iterator targets")
> Acked-by: Yonghong Song <yhs@fb.com>
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Applied. Thanks
^ permalink raw reply [flat|nested] 2+ messages in thread
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2020-05-14 5:51 [PATCH v2 bpf-next] bpf: fix bpf_iter's task iterator logic Andrii Nakryiko
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